Chemistry of Acenes, [60]Fullerenes, Cyclacenes and Carbon Nanotubes

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University of New Hampshire University of New Hampshire Scholars' Repository

Doctoral Dissertations Student Scholarship

Spring 2011

Chemistry of acenes, [60]fullerenes, cyclacenes and carbon nanotubes

Chandrani Pramanik University of New Hampshire, Durham

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Recommended Citation Pramanik, Chandrani, "Chemistry of acenes, [60]fullerenes, cyclacenes and carbon nanotubes" (2011). Doctoral Dissertations. 574. https://scholars.unh.edu/dissertation/574

This Dissertation is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. CHEMISTRY OF ACENES, [60]FULLERENES, CYCLACENES

AND CARBON NANOTUBES

CHANDRANI PRAMANIK

B.Sc., Jadavpur University, Kolkata, India, 2002

M.Sc, Indian Institute of Technology Kanpur, India, 2004

DISSERTATION

Submitted to the University of New Hampshire

in Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy

Materials Science

May 2011 UMI Number: 3467368

INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted.

In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Dissertation Publishing

ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 A En P. Miller, Dissertation director Pribfessor of Chemistry and Materials science

J c\ MO m • E • 'f "^ '-p~»~~

James E. Harper Professor of Physics and Materials Science

;/\ ./

Donald C. Sundberg / Emeritus Professor of Materials/ Science ^A_2^b5' Richard P. Johnson Professor of Chemistry

Karsten Pohl Professor of Physics and Materials Science

Date "If I find 10,000 ways something won't work, I haven't failed. I am not discouraged, because every wrong attempt discarded is another step forward".

—Thomas Edison

"Failure is the opportunity to begin again more intelligently."

— Henry Ford

in ACKNOWLEDGEMENTS

My thesis would be incomplete without expressing my sincere gratitude to certain individuals.

I owe my deepest gratitude to my advisor Prof. Glen Miller for his guidance, patience and endorsement, both intellectually and financially. I would never forget his consolations during one of those depressed days because of some failed reaction. But I want to thank him the most for providing me the opportunity to work in the various fields of materials science ranging from organic chemistry to nanotechnology. It was always great to learn from his amazing ability to channel his enthusiasm on a particular topic through his talks.

I want to dedicate my thesis to my parents Mrs. Ashrukana Pramanik and Late Joy

Narayan Pramanik whose blessings and inspiration still drag me the most. I would not have been able to walk this journey alone without the constant support and immense enthusiasm of my sister Dr. Indrani Pramanik and my brother-in-law Dr. Nilay Kundu, channeled through all those long distance telephone calls.

I can never thank enough my husband Jishnu Bhattacharyya for his constant encouragement. The tiniest bit of success in my research often excited him more than me.

He even gave me company sometimes when I was at work late at night. I would also like to express my sincerest thanks to my parents-in-law Dr. Saurindramohan Bhattacharyya and Mrs. Tapati Bhattacharyya and by brother-in-law Pratyush Bhattacharyya for their blessings and love.

iv I feel honored to have Prof. James Harper, Prof. Richard Johnson, Prof. Karsten

Pohl and Prof. Donald Sundberg in my thesis committee. Collaborating with Prof. Harper was a wonderful learning experience. Prof. Johnson's computation course has significantly contributed to my overall chemistry education. I am fortunate to have Prof.

Harper, Prof. Johnson, Prof. Miller, Prof. Sundberg and Prof. Charles Zercher as my teachers for various courses.

My heartiest thanks go to Dr. Ryan Kopreski for being my computation guru.

Without his help, a large part of my research would have remained incomplete. Ryan has been tremendously helpful to me during the preparations of this thesis, as well as with my review paper and proposal earlier. He is always available to discuss chemistry whenever the need be.

I would like to thank Jon Briggs for a very thorough review of my thesis. Thanks to Yushu Li for helping me with the last few clean-up reactions, to Yi Xu for always being so supportive and to Jeremy Kintigh, Julia Chan, Simka Ellis, Dr. Jennifer

Hodgson, Shunfu Hu, Dr. Weimin Lin, James Roane and Lei Zhou for discussions on research and random stuff.

The contribution of some past members of the Miller group towards my doctoral research is undeniable. It is a pleasure to acknowledge the help of Dr. Irvinder Kaur, Dr.

Wenling Jia and Dr. Michael Jadzyk for training me on several critical and sensitive organic syntheses as well as various analytical tools. I also want to thank Eman Akam,

Dr. Andrew Athans, Joe Dunn, Dr. Jun-fu Liu, Polina Prusevich, Dr. James Rainbolt,

Elizabeth Stairs and Nathan Stein for always being helpful and cooperative.

v Often when I felt deluded about chemistry, friendship kept it real. I am really thankful to my friends at UNH, Dr. Dana Filoti, Elizabeth Garcia, Srinivas Guntur,

Parikshit Junnarkar, Faraz Mehdi, Manasi Patil and Dr. Aveek Sarkar for being by my side. When things did not go right, it was always refreshing to talk to my buddies Dr.

Samanwita Pal, Karishma Jain, Susmita Basak, Debasmita Chaki, Manikarnika Kanjilal,

Payel Samanta and Saikat Chakraborti Thakur. I am indebted to my friends Dr. Priya Iyer and Dr. Anandarup Goswami for their priceless help in fetching me some valuable literature.

I am very thankful to Cindi Rower and Peg Torch for being so kind and helpful on innumerable occasions. My sincere thanks go to Bob Constantine for his willingness and eagerness to help all the time, to Cathy Gallagher, Dr. Patricia Wilkinson and John

Wilderman for always finding the time to teach me various analytical techniques including NMR, and to Nancy Cherim and Mark Townley for teaching me how to handle the TEM and the SEM.

Last but not the least I thank "National Science Foundation" and "Center for the

High-rate Nanomanufacturing" for funding me throughout my Ph.D career.

Thank you for reading my thesis!

VI TABLE OF CONTENTS

ACKNOWLEDGEMENTS IV TABLE OF CONTENTS VII LIST OF FIGURES XI LIST OF SCHEMES XV LIST OF TABLES XVIII LIST OF MOLECULES XX ABSTRACT XXX CHAPTER 1 1 1. SYNTHESIS AND STUDY OF ACENES, SUBSTITUTED ACENES, AND ACENE QUINONES 1 1.1 Introduction 1 1.1.1 Syntheses and State of the Art Applications of Acenes and Functionalized Acenes 2 1.1.1.1 Anthracene 3 1.1.1.2 Substituted Anthracenes and Their Applications 4 1.1.1.2.1 FETs with Functionalized Anthracenes 5 1.1.1.2.2 OLEDs with Anthracene Derivatives 7 1.1.1.2.3 Solar Cells with Functionalized Anthracenes 9 1.1.1.3 Tetracene 10 1.1.1.4 Substituted Tetracenes and Their Applications 11 1.1.1.5 Pentacene and Its Applications 15 1.1.1.5.1 FETs and Charge Carrier Mobility of Pentacene 17 1.1.1.5.2 Recent Advances with Pentacene in Other Applications 21 1.1.1.5.3 Drawbacks of Pentacene 22 1.1.1.6 Scope of Functionalized Pentacenes 23 1.1.1.6.1 FETs orTFTs of Functionalized Pentacenes 25 1.1.1.6.2 Other Applications of Functionalized Pentacenes 29 1.1.1.7 Larger Acenes 31 1.1.1.7.1 Hexacene 32 1.1.1.7.2 Functionalized Hexacenes 32 1.1.1.7.3 Heptacene 33

vii 1.1.1.7.4 Functionalized Heptacenes 35 1.1.1.7.5 Octacene, Nonacene and Functionalized Nonacenes 37 1.1.2 Theory behind Chemistry and Electronic Properties of Acenes 39 1.1.2.1 Stability and Reactivity of Acenes 39 1.1.2.2 Comparative Study of Reactivity of Acenes 40 1.1.2.3 Photodegradation of Acenes 41 1.1.2.4 HOMO-LUMO Energy and Band Gap of Acenes 43 1.2 Results and Discussion 48 1.2.1 Sulfur Stabilized Pentacene Derivatives 48 1.2.1.1 Synthesis of 3,3'-(Pentacene-6,13-diylbis(sulfanediyl))dipropanoic acid, an Intermediate for Making A Molecular Switch 48 1.2.1.1.1 Synthesis 49 1.2.1.2 Synthesis of S,S'-Pentacene-6,13-diyl diethanethioate, an Intermediate for Making Pentacene Oligomers with Disulfide Linkages 54 1.2.1.2.1 Synthesis 55 1.2.1.3 Pentacene-6,13-Disulfonium Salt 59 1.2.1.3.1 Attempts to Synthesize 6,13-Bis(n-dodecylthio)pentacene 61 1.2.1.4 Attempted Synthesis of 2,3,9,10-Tetrakis(benzylthio)-6,13- bis(phenylthio)pentacene 66 1.2.1.5 Theoretical Study of Thio-substituted Pentacenes 69 1.2.1.6 Conclusions and Future Work 71 1.2.2 Synthesis of Sulfur and Chloro Substituted Anthracene 72 1.2.2.1 Synthesis of 9,10-Bis(phenylthio)anthracene 72 1.2.2.2 Application to [60]Fullerene and Carbon Nanotubes 75 1.2.2.3 Future Direction and Conclusions 76 1.2.3 Towards the Synthesis of Larger Acenes; Sulfur-Stabilized Nonacene 76 1.2.3.1 Attempt to Synthesize 1,4,8,12,15,19-Hexa(4'-^-butylphenylthio)nonacene 78 1.2.3.2 Theoretical Studies of Arylthio Substituted Nonacenes 85 1.2.3.3 Conclusions and Future Direction 86 1.2.4 Spectroscopic Studies of Acene Quinones and Hydroxyacenes in Concentrated Sulfuric Acid 87 1.2.4.1 UV-Vis-NIR Study of Acene Derivatives in Concentrated Sulfuric Acid 88

vin 1.2.4.2 Proposed Mechanism 94 1.2.4.3 Conclusions and Future Direction 96 CHAPTER 2 97 2. SYNTHESIS AND STUDY OF CYCLACENES 97 2.1 introduction 97 2.1.1 Theoretical Studies of Cyclacenes 99 2.1.1.1 Semiempirical Studies and Aromatic Considerations 99 2.1.1.2 DFT Geometries and Electronic Configuration 100 2.1.1.3 Unique Properties for Odd and Even [«]Cyclacenes 102 2.1.1.4 Predicted Applications Based on Theoretical Study of Cyclacene 105 2.1.2 Past Attempts to Synthesize Cyclacene 106 2.1.3 Using [60]Fullerene-Acene Chemistry to Prepare a Cyclacene 109 2.2 Results and Discussion 113 2.2.1 Supramolecular Approach Towards the Synthesis of Cyclacenes 113 2.2.1.1 Synthesis of 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenylpentacene 114 2.2.1.2 Synthesis of Bis[60]Fullerene Adduct of 2,3,9,10- Tetrakis(benzyloxymethyl)-6,l 3-diphenylpentacene 120 2.2.1.3 Synthesis of Bis[60]Fullerene Adduct of 2,3,9,10-tetraiodomethyl-6,13- diphenylpentacene 121 2.2.1.4 Towards the Synthesis of [24]Cyclacene 124 2.2.1.4.1 Model Reaction with 1,4-Cyclohexanedione 125 2.2.1.4.2 Model Reaction with 1,4-Para-Benzoquinone 126 2.2.1.4.3 Model Reaction with Catechol 127 2.2.1.4.4 Model Reaction with 1,4-Benzenediamine and Derivatives of 1,4- Benzenediamine 128 2.2.1.4.5 Model Reaction with 1,2,4,5-Benzenetetramethanethiol 130 2.2.2 Theoretical Study of Substituted Cyclacenes 132 2.2.2.1 Evaluation of Methods using [10]Cyclacene 132 2.2.2.2 Theoretical Studies for Substituted [10]Cyclacenes and [18]Cyclacenes 134 2.2.3 Future Work to Synthesize Thio-functionalized Cyclacene 137 2.3 Conclusions 138

IX CHAPTER 3 139

3. C60 AND CNT CHEMISTRIES 139 3.1 Introduction 139 3.1.1 Allotropes of Carbon- [60]Fullerene and Carbon Nanotubes 139 3.1.2 Physical and Chemical Properties of Ceo and CNTs 143 3.1.3 Reactivity of Ceo towards Superacids 144 3.1.4 Reactivity of CNT towards Superacids 145 3.1.5 CNT Interactions with Latex Particles 146 3.2 Results And Discussion 149

3.2.1 C60 and CNT Chemistries with Fuming Sulfuric Acid (FSA) and Chlorosulfomc Acid (CS A) 149

3.2.1.1 Reaction of C6o with Fuming Sulfuric Acid and Chlorosulfomc Acid... 149 3.2.1.2 Reaction of MWNTs with Fuming Sulfuric Acid and Chlorosulfomc Acid 151 3.2.1.3 Future Direction 152 3.2.2 Self-Assembly of CNTs with Latex Nanoparticles 153 3.2.2.1 Summary and Conclusions 159 EXPERIMENTAL 160 REFERENCES 204 APPENDICES 223 Abbreviation 224 Spectra 226

x LIST OF FIGURES

Figure 1.1: The five known members of acene series 1 Figure 1.2: The numbering method of acenes: anthracene, tetracene and pentacene 2 Figure 1.3: Anthracene based transistors with their corresponding morphological images and transistor properties: mobilities (a), on/off current ratios and optical band gaps (Eg(opt)); (a) STM image of self-organized monolayers of 1 adsorbed at the n-tetradecane- HOPG interface, [10]— Reproduced by permission of The Royal Society of Chemistry, (b) Left: crystal packing diagram of 2; Right: overlap between adjacent molecules (viewed perpendicularly to the plane of anthracene). Protons are omitted for clarity. Reprinted ("in part") with permission from [11]. Copyright 2009 American Chemical Society (c) AFM topography of an as-spun thin film of 3; [12]— Reproduced by permission of The Royal Society of Chemistry. 7

Figure 1.4: Anthracene based semiconducting materials; promising candidates for OLED.15'16'17 8 Figure 1.5: (a) and (b) represent two configurations of FET devices, (c) model face-to- face arrangement of pentacenes, (d) crystal structure of bulk pentacene,54 (e) model monolayer structure of pentacene,54 images (d) and (e) are reprinted ("in part") with permission from [54]. Copyright 2004 American Chemical Society. 19

Figure 1.6: Symmetric and asymmetric functionalized pentacenes (25 - 71) 25 Figure 1.7: Molecular structure of substituted hexacenes.109'110 33 Figure 1.8: Comparison of the electronic absorption spectra of the acenes obtained from their corresponding photoprecursors in argon matrices at 10 K. Reprinted with permission from [114]. Copyright 2009 American Chemical Society. 35 Figure 1.9: Structure of functionalized heptacenes 36 Figure 1.10: Structures of nonacene derivatives.118 38 Figure 1.11: (a) and (b) Kekule's canonical structures of benzene; (c) resonance structure of benzene in VB theory; (d) incorrect representation of anthracene; (e) Clar's sextet representation of anthracene 39

Figure 1.12: Photodimerized "butterfly" product of (a) anthracene, (b) tetracene and (c) pentacene 43 Figure 1.13: Illustration of bonding antibonding interrelation between the HOMO-LUMO levels of two ethylene molecules in a cofacial configuration and the formation of valence

XI and conduction bands when a large number of stacked molecules interact (top); Semi- classical charge transfer theory shown in equation (bottom).131 45 Figure 1.14: (a) Singly occupied orbitals of decacene (UB3LYP/6-31G(d)). Reprinted with permission from [136]. Copyright 2004 American Chemical Society, (b) Molecular orbitals, HOMO and LUMO of pentacene (DMRG). Reprinted 'in part' with permission from [137]. Copyright 2007 American Chemical Society. 47

Figure 1.15: Pentacene based molecular switch based on EC mechanism 48

Figure 1.16: UV-Vis spectra, NMR spectra of 88 in MeOH and CD3OD at top and NMR spectra of 89 in CD3OD at bottom with expected peaks for 88 marked with the asterisks. 53 Figure 1.17: UV spectra of 91 in CHCI3 (top) and !H NMR of mixture containing 91 in CDCI3 with expected peaks marked with asterisks 58 Figure 1.18: UV-Vis spectrum (top) and NMR spectra (bottom) of 96 in CDCI3 (expected peaks for 96 has been marked with asterisks) 65 Figure 1.19: Structure of hexathio-substituted pentacene 100 66 Figure 1.20: UV-Vis and CVof 118 (left) and 117 (right) 82 Figure 1.21: Mass spectrum and UV-Vis spectrum (inset) of 116 83 Figure 1.22: Mass spectrum of 129 84

Figure 1.23: UV-Vis spectra of pentacene in DCM (left) and 23 in cone. H2S04 (right). 88 Figure 1.24: The structures of acene quinones and hydroxyacenes whose properties in cone. H2SO4 are studied 89 Figure 1.25: The combined UV-Vis-NIR spectra plotted for (a) acene quinones and (b) acene diols in cone. H2SO4 with respect to increase of n 91 Figure 1.26: Plots of A^ax-values at longest wavelength of solution of acene monoquinones (red circle), acenediols (blue triangle) in cone. H2SO4 and reported X^ax of acenes (black square) (A,max -values of acenes in DCM are taken from ref-13 for n=3,4,6, and from ref-113 for n=7 and n=5) 92

Figure 1.27 Plots of Xmax-values at longest wavelength of solution of acene diquinones (red circle), acenetetrols (black square) in cone. H2SO4 93

Figure 1.28: Decrease of A^axOf 23 in cone. H2S04 with respect to gradual addition of 52 drops of H2O in presence of light and air. 94 Figure 1.29: The proposed mechanism of (a) acid treatment of 23, (b) 24, and (c) the xii mechanism of water neutralizing the cationic state of 23 in cone. H2SO4 medium 95 Figure 2.1: [10]Cyclacene 147; equatorial belts of (a) C78 representing [9]cyclacene and (b) C84 representing [10]cyclacene moiety (71 -bonds omitted for clarity) 97 Figure 2.2: (a) Open-ended (10,0) Zigzag SWNT and [10]cyclacene (147) 98 Figure 2.3: [6.8]3cyclacene 99 Figure 2.4: (a) [20]trannulene, (b) [10]Cyclacene (147) 101 Figure 2.5: Magnetic susceptibility (x) of [n]cyclacenes vs. n. Inset: Table of the plotted data.182 103 Figure 2.6: Highest occupied a (left) and P (right) orbitals of [8]-cyclacene at the BS M06-L/6-31 G(d) \eve\.[184J- Reproduced by permission of The Royal Society of Chemistry. 105 Figure 2.7: Degenerate pairs of highest occupied a (left) and P (right) orbitals of [9]- cyclacene at the BS M06-L/6-31 G(d) level. [184]- Reproduced by permission of The Royal Society of Chemistry. 105

Figure 2.8: Acene-[60]fullerene mono adducts.201'202'203 110 Figure 2.9: (a) Earlier proposal for synthesis of a phenyl-substituted -cyclacene via closure of pentakis[60]fullerene adduct; (b) iterative coupling of cyclacenes to produce SWNCs.169 112 Figure 2.10: Proposed path for synthesis of phenyl substituted [24]cyclacene 113 Figure 2.11: Cyclic voltammetry of 175 119 Figure 2.12: The time dependent UV spectra of 175 over 84 minutes 119 Figure2.13:(a)1Hand(b)13Cofl84 123 Figure 2.14: B3LYP/6-31G* optimized cyclacenes 135 Figure 3.1: (a) Structure of [60]fullerene; (b) bisadduct nomenclature as developed by Hirsch.223 140 Figure 3.2: (a) single walled nanotube; (b) multi walled nanotube 141 Figure 3.3: Images of (a) armchair, (b) zigzag and (c) chiral nanotubes, where chirality is defined by 6 and tube properties are defined by a combination of d and 6 142

Figure 3.4: Mono /?-sultone of C60,E = 700.33 Kcal/mol (PM3) 144 Figure 3.5: TEM of functionalized-MWNT adhered to the sidewall of PSNC through xiii hydrogen bonds. Reprinted ("in part") with permission from [270]. Copyright 2004 American Chemical Society 147 Figure 3.6: (a) Scheme of the preparation of the carbon nanotubosomes (b) SEM images of the 9.6 jum sulfate latex PS particles coated with NH2-functionalized MWNTs (c) SEM images of the obtained CNT capsules after the dissolution of the PS particle templates. Reprinted ("in part") with permission from [271]. Copyright 2005 IOP Publishing Ltd. 148

Figure 3.7: IR spectra of (a) polysultonated C6o and (b) from the reaction by refluxing Ceo in FSA. The IR spectra of (c) the chlorinated C6o256 and (d) the brown solid recovered from the reaction by refluxing C6o in CSA. Figure (a) and (c) are reprinted with permission from [256]. Copyright 1994 MRS E-Proceedings 150 Figure 3.8: TEM images of (a - c) pristine MWNTs; (d - f) MWNTs reacted with CSA; and AFM images of (g) pristine MWNTs and (h) MWNTs reacted with CSA on graphite (courtesy Dr. Jun-Fu Liu) 152 Figure 3.9: SEM Images of SWNTs (from Nantero Inc., USA) and (a) bare, (b) carboxylated and (c, d) amino terminated PSL composites on carbon substrates 155 Figure 3.10: SEM images of self-assembled monolayers of SWNTs and amino terminated PSL composites on carbon substrates by (a and b) 'drop-and-dry' and (c and d) 'dip-and- dry' methods after diluting solution mixture of both SWNTs and PSL 156 Figure 3.11: The SEM images of the self-assembly of SWNTs and amino terminated PSL on (a - c) silica, on (d) gold and aluminum (L-R) and on (e, f) mica. The SEM images of bare Au (g), Al (h) and mica (i) substrate before any treatment 157 Figure 3.12: SEM images of electrophoretic self assembly of (a) amino functionalized PSL and (b) bare PSL. Experiments performed at Northeastern University. 158

xiv LIST OF SCHEMES

Scheme 1.1: Anthracene from anthraquinone 3 Scheme 1.2: Synthesis of 9,10- disubstituted anthracene derivatives.9 5 Scheme 1.3: Synthesis of tetracene 11 Scheme 1.4: Substituted tetracene compounds useful for electronic applications 14

no Scheme 1.5: The very first synthesis of pentacene by Clar. 16 Scheme 1.6: Common methods to synthesize pentacene 17 Scheme 1.7: Two common pathways (a and b) to synthesize functionalized pentacenes. 24 1 OR Scheme 1.8: Synthesis of Hexacene 32 Scheme 1.9: Photochemical synthesis of heptacene, isolated in PMMA matrix.113 34 Scheme 1.10: Photooxidation of acenes in two different pathways, namely concerted and stepwise 41 Scheme 1.11: Synthetic scheme of pentacene 88 49 Scheme 1.12: Proposed scheme for synthesizing 6,13-pentacenethiol 90 and disulfide linked pentacene oligomer. 55 Scheme 1.13: Synthetic scheme of pentacene 91 56 Scheme 1.14: Synthesis of 93 59 Scheme 1.15: Retro synthetic scheme of synthesis of 97 from 95 and 96 60 Scheme 1.16: Synthesis of phenyl sulfonium salt from thiophenol and 1,4-dibromobutane 60 Scheme 1.17: Mechanism and retro-synthetic analysis of 97 from 95 and 96 61 Scheme 1.18: Synthesis of 98 from 24 and 95 from 98 62 Scheme 1.19: Synthesis of 99 from 24 and 96 from 99 63 Scheme 1.20: Synthesis of aldehyde 104 from 4,5-dichlorophthalic acid 67 Scheme 1.21: Attempted Synthesis of pentacene 100 from aldehyde 104 68 Scheme 1.22: Synthetic scheme of pentacene 109 from 106 69 xv Scheme 1.23: Arylthiolation of aromatic compounds using disulfide.156 72 Scheme 1.24: Synthesis of diphenylthioanthracene 110 73 Scheme 1.25: Reaction of pentacenes with SbCls and diphenyl disulfide 74 Scheme 1.26: Reaction of SbCls with (a) C6o and diphenyl disulfide, (b) Ceo only, and (c) MWNT and diphenyl disulfide 76 Scheme 1.27: Retrosynthetic analysis of 115 from 116 77 Scheme 1.28: (a) Synthetic approach of 117 from 118 and 119 and (b) reported synthesis of nonacenediquinone 78 Scheme 1.29: Syntheses of 118 and 119 79 Scheme 1.30: Synthesis of 128 80 Scheme 1.31: Synthesis of 117 81 Scheme 1.32: Equation of synthesis of 116 from 117 83 Scheme 1.33: Synthesis of 129 from 116 84 Scheme 2.1: Stoddart's attempt to synthesize [12]cyclacene194 107 Scheme 2.2: Cory's attempt to synthesize hexyl-substituted [8]cyclacene.195'196 108 Scheme 2.3: Schluter's synthesis of a substituted [18]cyclacene derivative.197 109 Scheme 2.4: [60]Fullerene adduct of o-quinodimethane 109 Scheme 2.5: Synthesis of bis[60]fullerene adduct 168 of 6,13-diphenylpentacene by Miller and Mack.204 Ill Scheme 2.6: Synthesis of cz's, c«-tris[60]fullerene adduct, 169 by Miller and Briggs.207111 Scheme 2.7: Retro-synthesis of the targeted bis[60]fullerene adduct 172 114 Scheme 2.8: Synthesis of 3,4-bis(benzyloxymethyl)furan 177 115 Scheme 2.9: Synthesis of 180 from 177 116 Scheme 2.10: Synthesis of the new end protected functionalized pentacene 175 via synthesis of new intermediates (181, 182 and 183) 117 Scheme 2.11: Synthesis of bis[60]fullerene adduct 174 from 175 121 Scheme 2.12: Synthesis of alcohols from corresponding ethers using TMSI.212 121

xvi Scheme 2.13: Synthesis of bis-C6o adduct 184 of 2,3,9,10-tetraiodomethyl-6,13- diphenylpentacene 122 Scheme 2.14: Coupling reaction through nucleophilic substitution. In step (c) iodomethylbenzene and 1,4-cyclohexanedione are shown for clarity. 124 Scheme 2.15: Model reaction with 1,4-cyclohexanedione 126 Scheme 2.16: Model reaction with 1,4-para-benzoquinone 127 Scheme 2.17: Model reaction with catechol 127 Scheme 2.18: Model reaction with aniline 128 Scheme 2.19: Model reaction with 1,4-diaminobenzene 128

Scheme 2.20: Model reaction with (a) diaminodurene and (b)jp,/7-diaminobiphenyl... 129 Scheme 2.21: Attempted synthesis of highly soluble octadecyl substituted diamino benzene 197 130 Scheme 2.22: Model reaction with 1,4-diaminobenzene 131 Scheme 2.23: 1,2,4,5-benzenetetramethanethiol 198 131 Scheme 2.24: Reaction of bis [60] fullerene adduct 184 with 198 131 Scheme 2.25: Synthetic approach of thio-substituted pentacenes 209 138

xvn LIST OF TABLES

Table 1.1: Anthracene functionalized single and polymeric doner materials for solar cell with their corresponding device and material properties (n, (j,hoie, Eg(oPt)) with respect to different ratios of acceptor material 10 Table 1.2: FET properties and crystal packing structures of some selected functionalized pentacenes 28 Table 1.3: OLED properties of some selected functionalized pentacenes and Alq3 30 Table 1.4: The Diels-Alder rate constant and relative reactivity of acenes.122 40 Table 1.5: List of observations for the attempted aromatization of 89 51 Table 1.6: List of observations for the aromatization of 92 57 Table 1.7: List of reactions utilized to aromatize 99 and synthesize pentacene 96 64

Table 1.8: Calculated energies of HOMO, LUMO, Egap and Eg(opt) (in eV) of 44, 88, 90, 91, 96 and 100 using B3LYP/6-311+G**// B3LYP/6-31G* level; The values of pentacene using B3LYP/6-311+G**// B3LYP/6-31G* level were taken from 46a; The values of pentacene and 44 using B3LYP/6-311+G**// PM3 level were taken from 93b 71 Table 1.9: Percent yields of different products isolated from the reaction of a Scheme 1.24, calculated from their respective NMR spectra 74

2 118 Table 1.10: The energies of HOMO, LUMO, Egap, (in eV) and ~~of nonacene , 130, 131 and 132118 calculated using the B3LYP/6-311+G**// B3LYP/6-31G* method are listed 86~~

Table 1.11: List of acene derivatives treated with cone. H2SO4 and measured Amax values with solution color at RT and fluorescence color under UV light 90 Table 2.1: Relative ground state energies (kcal/mol) of [n]cyclacenes in their open shell 185 singlet (Sos), closed shell singlet (Scs) and triplet (T) states. 102 Table 2.2: Calculated values (unit less) of for BS DFT calculations on singlet [n]cyclacenes with the M06-L/6-31G(d) basis set.185 104 Table 2.3: Experimental (UV-VIS and CV) and calculated physical properties of pentacene 175 including Xmax, tm, oxidation potential (Ox.) and reduction potential (Red.), energies of HOMO, LUMO and band gap (Eg(opt), Eg(cv) and Egap are listed 118

~~2 Table 2.4: The SPE, HOMO, LUMO energies, the HOMO-LUMO gap (Egap) and~~

xvm values before and after3 annihilation of the first spin contamination for [10] cyclacene. Observation 3 taken from Chen and coworkers. Parenthetical percentages are percent deviation with respect to obs. 3.185 133

2 Table 2.5: The HOMO, LUMO energies, the HOMO-LUMO gap (Egap) and ~~values beforeb and after3 annihilation of the first spin contamination, for respective cyclacenes using UB3LYP/6-311+G**//B3LYP/6-31G* 136~~

~~xix LIST OF MOLECULES~~

~~Chapter 1~~

~~C.H,~~

~~PfiH,~~

~~C H 6 l3O^J = ^ //• •\ /^OC6H13~~

~~C6H130 7 OC6H13~~

~~\_J? R,0 10~~

~~R,=R2= Octyl, R3=R4=2-ethyIhexyle~~

~~XX o ^ o R R = 2,6-diisoproPyl R' = 4-(t-octyl)Phenoxy HO H 24 O 23~~

XXI D R: ^R3 R:-S R: 28 R3= wBu 33:: R33== Si(iPr)3 40: R5= CH3 29 R3= n-pentyl 34:: R33== SiOPr)2Et 39 41: R5= (CH2)4CH3 30 R3= «-hextyl 35: R3= Si(;Pr)2(n-Bu) 25 R,= R2 = H 42: R5= (CH2)7CH3 31 R3= n-octyl 36- R3= Si(;Pr)2(sec-Bu) 26- Ri = H, R2 = nPr 43: R5= (CH2)9CH3 32 R3= n-decyl 37: R3= Si(;Pr)2(n-Hex) 27: R,= B, R, = tBu 44: R5= Ph 38: R3= Si(!Pr)2(n-Oct) r 45: R5= (CH2)2SiMe3

~~Si( Pr) Si((Pr)3 ; 3~~

~~Q oxz 46: R= R)= R = R4 = H, R = R = CH 3 2 5 3 57 58 47. Rj= R3= R4 = H, R2= CI, R= o-dimethylPhenyl Si((Pr)3 Si(~~

~~XX11 SiR, ccccoo 73:R = ;Bu 77: R = -Si(«Bu)3 74: R = cycloPentyl g^ 75: R = cyclohexyl 78: R = -Si(SiMe3)3 76: R = SiMe3~~

~~Ph R~~

~~XX111 BnS^z-^CHjOH BnS-^/^CHO~~

~~BnS^^CHO 104~~

~~H. „OH H SPh BnS BnS t SBn~~

~~BnS BnS SBn~~

~~BnS~~

~~BnS 111~~

~~XXIV S>J SAJ sAj C>U c~~

~~SPh SPh SPh SPh~~

~~SPh SPh 132 SPh SPh~~

~~XXV O [i :\\~~

~~O 133~~

~~136 OH OH 137~~

~~XXVI Chapter 2~~

~~XXVll OBn OBn~~

~~OBn Ph I" OBn~~

~~OBn QBn OBn Bn OH HOH,C. V^C0 Me C0 Me Co 2 2 HOH,C P M CO,Me OBn OH 176 ( C02Me OBn 77 179 180 OBn l" OBn n8~~

~~OBn OBn XT ( CHO OBn O 182 OBn OBn H0 Ph 183 QBn OBn 181~~

~~CH2I~~

~~BOX 185 CH2I BO,C 187 ccO coo coco O 188 •18 o9„ OI 190 191 000-00 O&CO oo-o->co 192 F19\3 194~~

~~NO, , N02 NH, Br' Br 17 17 x^ £ I x^7 $ \\ Br^ Br ^jX^^X^ >jX X 17 ^ 17 xir. 17 NH 7 195 N02 N02 197 2 196 (X=SorO)~~

~~SH SH Br Br CO CCs SH 198 SH 199 200 Br 201 Br~~

~~XXVlll 202 'V* 203 fy 2M ^~~

:5 *P ^ */*>• **» J* *J ***

~~205~~

****** *** a««» irmjj J5P -**» t

~~207 208~~

~~C 2H OBn s ° OBn OBn HQ R OBn OBn ROc02H QBn )cc^x^ )xooq ^OOQX( OBn OBn OBn H H 210 209^CO2H ° °BnOBn ^ ^C02U°^~~

~~XXIX ABSTRACT~~

~~CHEMISTRY OF ACENES, [60]FULLERENES, CYCLACENES~~

~~AND CARBON NANOTUBES~~

~~by CHANDRANI PRAMANIK University of New Hampshire, May, 2011~~

~~In the present work, we studied the chemistries of acenes, cyclacenes,~~

[60]fullerenes and CNTs. Acenes are well known organic semiconductors. Pentacene is a benchmark organic semiconductor due to low HOMO-LUMO gap and high charge carrier mobilities in its thin film. Its poor solubility and instability, however, limit its utility and overall cost effectiveness. We successfully synthesized several sulfur- functionalized acene derivatives that overcome these problems. However, we also encountered difficulties to aromatize some of these derivatives. To circumvent these problems, we studied some new synthetic routes to sulfur-functionalized anthracenes, pentacenes and nonacenes. Additionally, the electronic properties of substituted acenes were compared using high level DFT calculations. According to our unrestricted DFT calculations, significant spin characters associated with thio-substituted nonacenes are likely the reason for their instabilities and difficult syntheses. Our UV-Vis-NIR studies reveal acene characteristics in acene quinones and hydroxyacenes that are dissolved in concentrated sulfuric acid.

~~XXX Cyclacenes may be useful precursors to synthesize SWNTs with uniform dimensions. We explored the supramolecular assembly of a bis[60]fullerene adduct of a~~

~~2,3,9,10-tetrasubstituted pentacene as a method to produce a [24]cyclacene framework.~~

To that end, we synthesized the bis[60]fullerene adduct of 2,3,9,10-tetraiodomethyl-6,13- diphenylpentacene. The synthesis of a cyclacene framework via intermolecular cycloaddition of bis[60]fullerene adducts requires further study. According to our unrestricted broken symmetry calculations for different functionalized [«]cyclacenes,

~~HOMO-LUMO gaps and spin characters are impacted by the presence and location of alkylthio and/or arylthio functional groups on the [«]cyclacene skeleton.~~

[60]Fullerene is known to form polysultone and chlorinated derivatives when treated with fuming sulfuric acid (FSA) and chlorosulfomc acid (CSA), respectively, at room temperature. Based on our preliminary study, we predict that MWNTs react with boiling CSA and they are unreactive toward boiling FSA. The CSA treated MWNTs showed less bundling and broken tips in their AFM and TEM images. We studied the self-assembly of carboxylated-SWNTs and polystyrene latex (PSL) particles on different substrates. We believe that carboxylated-SWNTs have stronger interactions with amino or carboxy terminated PSL than unsubstituted PSL particles. According to our SEM analysis, self-assembly of the nanocomposites is moderately substrate dependent.

~~xxxi CHAPTER 1~~

~~1. SYNTHESIS AND STUDY OF ACENES, SUBSTITUTED ACENES, AND~~

~~ACENE QUINONES~~

~~1.1 INTRODUCTION~~

Acenes are a family of organic molecules belonging to the class of compounds known as polycyclic aromatic hydrocarbons (PAHs). They are composed of "alternant cata-annelated" or "alternant cata-condensed" benzene rings fused in a linear fashion.l"2^

The smallest acene is anthracene, which contains three, fused benzene rings. The largest experimentally known unsubstituted acene is heptacene, containing seven linearly fused benzene rings. The known unsubstituted acenes are listed in Figure 1.1. ' "

~~Anthracene Tetracene Pentacene~~

~~Hexacene Heptacene~~

~~Figure 1.1: The five known members of acene series~~

The name acene was coined4 by Eric Clar, widely regarded as the father of modern PAH chemistry. Early contributions to the naming of higher PAHs came from 1 many scientists including Scholl,? Stelzner and Kuh.6 However, Eric Clar unified and refined the nomenclature of PAHs including the acene family.l The members of acenes containing four or more fused benzenoid rings are named systematically using a Greek prefix to denote the number (n) of fused benzene rings and the common suffix "acene," as in tetracene, pentacene, hexacene and so on (Figure 1.1). The 3-ring acene, anthracene, is the only exception to this naming scheme.

Beyond the parent acenes, chemists are also interested in their functionalized derivatives. Thus, for consistent nomenclature of the substituted acenes, a numbering scheme is used to label the carbon atoms in an acene molecule which are chemically bound to hydrogen atoms or other substituents (Figure 1.2).

~~8 9 1 10 11 12 1 11 12 13 14 1~~

~~5 10 4 7654 87654 Anthracene Tetracene Pentacene~~

~~Figure 1.2: The numbering method of acenes: anthracene, tetracene and pentacene~~

~~1.1.1 Syntheses and State of the Art Applications of Acenes and Functionalized~~

~~Acenes~~

Acenes are semiconductors by nature making them appropriate candidates for organic electronic applications. However, their poor solubility and stability limit processability and thus prohibit the manufacture of devices in a cost-effective and convenient way. Attempts to improve processability of acenes through functionalization are reviewed in this section. 2 1.1.1.1 Anthracene

Anthracene is a colorless crystalline solid1 that exhibits strong violet fluorescence in organic solvents. Anthracene is a semiconductor under ambient conditions, but when irradiated with light of wavelength 366-400 nra, it becomes a conductor.1'7 Anthracene was first discovered by Dumas and Laureant in 1832 using fractional distillation of coal- tar above 270 C.1 Since its discovery, anthracene has undergone extensive synthetic and theoretical studies. Due to its facile isolation from natural sources, anthracene can be obtained in bulk quantities. Anthracene has also been produced by pyrogenic1 processes using acetylene, acetylene and benzene, styrene and benzene, phenol, toluene, or oil of turpentine and petroleum residues as fuels.1 There are also many synthetic approaches by which to produce this molecule. According to Clar, the best method to prepare ultrapure anthracene for scientific needs, particularly for spectroscopic studies, is to begin with synthetic anthraquinone then to reduce it to anthracene using zinc dust and ammonia or zinc-dust fusion (Scheme 1.1). It is beyond the scope of this text to describe all synthetic methods of anthracene in detail, and readers are recommended to review Clar's book.

~~O Zn° (f^V^f^l~~

~~Scheme 1.1: Anthracene from anthraquinone1~~

~~Due to its high oxidation potential and promising optical and electronic properties, anthracene became popular in photochemistry and organic electronics in the~~

~~3 past two decades. The interested reader is directed to John Anthony's 2006 review of the applications of anthracene and its derivatives for further details.~~

~~1.1.1.2 Substituted Anthracenes and Their Applications~~

~~Extensive studies have been conducted to functionalize anthracene. The 9,10- positions of anthracene (Figure 1.2) are more reactive than the other available positions.9~~

~~Some recently reported, one-step reactions to prepare functionalized anthracenes are listed below (Scheme 1.2). The products of these reactions are precursors to further functionalized anthracenes.~~

Because of their high oxidation potential, high solubility, and ease of functionalization, anthracene and its derivatives have shown promise in organic electronic applications. To demonstrate how functionalization of acenes can affect device properties, some recent functionalized anthracene systems are discussed below.

~~4 NBS, LiClQ4, DCM, RT, 5 min, Yield: 100% Rf: 9 (a) "~~

~~HBr, NH4NO3, H20, RT, lhr, Yield: 100% ^ Rf: 9 (b) "~~

~~Br2, DCM, RT to 0 °C, lhr, Yield: >96% R~~

~~K3Fe(CH)6, Me2NCH2CH2NH2, NaC03, PdCl2 1 1 -Butyl-1 -methylimidazolium tetrafluoroborate Yield: 64%, Ref: 9 (d) CN~~

~~CH2C1~~

~~(CH20)n, HC1, Dioxane, Reflux, 16hr, yield: 60% Ref: 9 (e)~~

~~CH2C1~~

~~Scheme 1.2: Synthesis of 9,10- disubstituted anthracene derivatives.'~~

~~1.1.1.2.1 FETs with Functionalized Anthracenes~~

Several reports of thin film devices suggest that addition of functional groups to the organic molecules, especially to acenes, can effectively tune the morphology of the resulting thin film and thus change the device properties. Torsi and coworkers synthesized several 9,10-disubstituted anthracene compounds from 9,10- dibromoanthracene. ' They built a series of decyl-functionalized, 9,10-ter- anthryleneethynylene 1 (Figure 1.3 (a)) based organic thin-film transistor (OTFT) in bottom- and top-contact configurations (Section 1.1.1.5). Using spin coating, they achieved a STM image of a highly ordered self-assembled organic monolayer of 1 on highly orderedpyrolytic graphite (HOPG). However, the mobilities and the on/off current ratios for their devices were not exceptional (Figure 1.3 (a)). Recently, Wang and coworker also synthesized nearly planar, anthracene-based 'cruciform' ' anthracene semiconductor 2 (Figure 1.3 (b)). Their studies also confirmed that the substituent effect along one axis to the cruciform (9,10-positions of anthracene) can affect the self- assembly properties of the molecules. Single crystal micro/nano structural morphologies were controlled by the K-K interactions among the molecules (Figure 1.3 (b)). A high- performance, single-crystal field effect transistor (FET) of 2 could be achieved with charge carrier mobility as high as 0.73 cm2/Vs. Similar studies by Park and coworkers with the introduction of (5-hexylthiophenyl)ethynyl groups at the 2,6-positions of anthracene and hexyl groups at the 'para'1 position of both phenyl rings in 3 (Figure 1.3

(c)) caused a tight arrangement of the molecules along the lateral direction (AFM image is shown in Figure 1.3 (c)). This demonstrated a device property with a high on/off current ratio of 5.4xl06.12 The reported mobility of 3 (0.24 cm2/Vs) is less than that of 2 but is nonetheless impressive given that the thin-film of 3 was spin coated. The challenge and control of self-assembly properties of these organic molecules are better understood by these studies, and that is one of the advantages of organic semiconductors over inorganic ones.11 Moreover the devices made with anthracene derivatives are quite competitive with respect to an amorphous silicon device having electronic mobilities on the order of 0.5-1 cm /Vs and an on/off current ratio of 10 .

6 Figure 1.3: Anthracene based transistors with their corresponding morphological images and transistor properties: mobilities (u), on/off current ratios and optical band gaps (Eg(opt)); (a) STM image of self-organized monolayers of 1 adsorbed at the rc-tetradecane- HOPG interface, [10]— Reproduced by permission of The Royal Society of Chemistry, (b) Left: crystal packing diagram of 2; Right: overlap between adjacent molecules (viewed perpendicularly to the plane of anthracene). Protons are omitted for clarity. Reprinted ("in part") with permission from [11]. Copyright 2009 American Chemical Society (c) AFM topography of an as-spun thin film of 3; [12]— Reproduced by permission of The Royal Society of Chemistry.

~~1.1.1.2.2 OLEDs with Anthracene Derivatives~~

Having a high oxidation potential and a high fluorescence quantum yield (>0.64 for single crystal of anthracene),14 anthracene is a potential candidate for light emitting systems. Zhang and coworkers made a blue light-emitting diode from anthracene triphenylamine derivative 4 (Figure 1.4). This has a maximum luminous efficiency as

~~7 high as 7.9 cd/A and maximum brightness (luminance) up to 10000 cd/m.2 15~~

Simultaneously, they made a single-emitting component for white organic light emitting diode (OLED) using anthracene derivative 5 (Figure 1.4) with a maximum luminous efficiency of 7.0 cd/A and a maximum brightness of 12320 cd/m2 at 8V.16 This is significant, because the white emissions from white OLEDs are generally composed of a combination of blue, red, and green emissions from isolated molecular systems. More recently, Reddy and coworkers also prepared a three-layer OLED device, with an n-type semiconductor 6 consisting of a 9,10-disubstituted anthracene functionalized with phenyloxadiazole group (Figure 1.4), having a higher maximum brightness of 13450 cd/m2 with a maximum luminous efficiency of 15.20 cd/A at 16 V.1' These OLED components are comparative to the standard n-type component tris(8-

'y hydroxyquinolinato)aluminum (Alq3); with a maximum brightness of 10220 cd/m and a maximum luminous efficiency of 24.90 cd/A at 19 V17 For reference, standard frosted light bulbs are typically on the order of 100,000 cd/m and the sky when heavily overcast is about 1000 cd/m2z. IS

~~Luminous efficiency =7.9 cd/A Luminous efficiency =7.0 cd/A Luminous efficiency =15.2 cd/A Max. luminance = 10000 cd/m2 Max. luminance = 12320 cd/m2 Max. luminance = 13450 cd/m2~~

~~Figure 1.4: Anthracene based semiconducting materials; promising candidates for 0LED_ 15,16,17 1.1.1.2.3 Solar Cells with Functionalized Anthracenes~~

Anthracenes and other organic ^-conjugated molecules have also become popular for photovoltaic devices due to their low-temperature solution-processability and compatibility with plastic substrates. Several attempts have been made at bulk heterojunction solar cells with both low dimensional (single molecule, 7, Table 1.1) " and polymeric (8, 9, 10 in Table l.l),21'22 highly ^-conjugated anthracene derivatives as donor materials, combined with [6,6]-phenyl C6i-butyric acid methyl ester (PCBM) as an acceptor material. Hoppe and coworkers studied and established a correlation between photovoltaic performance and several intrinsic properties of the materials such as ability to n-n stack, the absorption behavior, the charge carrier mobility and active layer nanoscale morphology.23 They have synthesized and characterized eight anthracene- containing copolymers bearing different side chains and found power conversion efficiency (PCE) up to 3.14%. These results indicate the need to improve the PCE of organic solar cells to compete with commercially available silicon solar cells with PCE up to 20%.24 Some recent anthracene derivatives (7 to 10) used to make solar cells are listed in Table 1.1, with values of their ratio with respect to PCBM, PCE (n), hole mobility (Uhoie) and optical band gap (Eg(0pt)).

~~9 Molecule (donor material) Donor ri(%) Pholc Cg(opt) PCBM [cm2/(Vs)] (eV)~~

~~11 1 17 CsHtP-^~~

~~C6H,30 OC5H13~~

~~'O 1-3 02 7.1xl0-: 2 05 / V~~

~~OC6H. 1-3 2 1 2 38 J 5«H13o'~~

~~OR, PR8 /- 1:2 3 14 2 57x10-' 1 80 10 //~i O B'°'' R,-R3- Ocyl Rs=R4=2-ethyihexyte~~

Table 1.1: Anthracene functionalized single and polymeric doner materials for solar cell with their corresponding device and material properties (n, p,hoie, Eg(opt)) with respect to different ratios of acceptor material.

~~1.1.1.3 Tetracene~~

Tetracene is a bright orange amorphous solid which crystallizes from xylene in yellow leaflets and can readily sublime above 170 °C.° It exhibits green fluorescence in solutions of organic solvents and gives a moss green color in concentrated sulfuric acid.

~~Unlike other acenes, tetracene is not carcinogenic.1 Tetracene is also an organic semiconductor and shows photoconductivity.'~~

~~Tetracene can be isolated from various natural sources (e.g., natural petroleum distillates, coal tar, diesel exhaust25 and char-grilled beef).26 Tetracene was first~~

10 synthesized in 1897," and several other methods of synthesis have since been established. According to Clar, the simplest preparation of tetracene involves condensation of phthalic anhydride with tetralin via Friedel-Crafts acylation followed by reduction of the resulting keto-acid and ring-closure to produce 5,12-dihydrotetracene.

~~Dehydrogenative aromatization by chloranil or heating with Cu in the final step yielded tetracene (Scheme 1.3).~~

~~A1C13> [f^Yl^^^ Zn, NaOH~~

~~o$*co C02H O~~

~~Scheme 1.3: Synthesis of tetracene~~

~~1.1.1.4 Substituted Tetracenes and Their Applications~~

A well-known example of tetracene functionalization includes halogenations followed by Suzuki-coupling. Synthesis of mono-bromotetracene 11 in good yield (90%) was reported by Bardeen and coworkers (Scheme 1.4)/ The syntheses of bis(tetracene) molecules 12 and 13 with phenyl or biphenyl linkers were also reported. Compounds 12 and 13 are claimed to be promising "exciton fission" molecules for photovoltaic cells, which involves a new mechanism of multiple exciton generation (MEG) to increase the yield of excitations per absorbed photon.29

11 For more than one substitution-reaction (e.g. chlorination) 5,11-positions are more efficient than 5,12-positions of tetracene.1 However, Kyushin and coworkers were able to produce both 5,12- and 5,11-dibromotetracene (14 and 15 respectively) using CuBr2

(Scheme 1.4).",0 With further modification they isolated 5,11- and 5,12- bis(diisopropylsilyl)tetracene (16 and 17). Both derivatives 16 and 17 show intense yellow-green fluorescence with a quantum yield almost two times higher than that of

= tetracene (A^ax 473 run) and a bathochromic shift (Xmax = 504 nm for 16 and ^max = 501 nm for 17). In the same year, Mullen and coworkers isolated dibromoanthracene 15 in much higher yields (92%) using NBS in a DMF-chloroform mixture.31 Suzuki-coupling followed by cyclo-dehydrogenation of 15 yields a new class of core extended perylene chromophores or near-IR (NIR) dyes. One example of this novel, highly soluble and very stable perylene-tetracene-perylene molecule 18, is shown in Scheme 1.4. The absorption maximum of 18 is influenced by the four phenoxy substituents (Xmax = 567 and 1037 nm) and lies in the same region of the emission spectrum of a Nd-YAG laser. This class of molecules is highly promising for the laser welding of polymers and useful for heat-ray blockers, with applications in car windscreens, architectural glasses and agricultural films.31

The above mentioned reactions are focused on mono- or di-functionalization selective to the middle benzenoid rings of the tetracene. However, selective difunctionalization of tetracene at the 2,8- and 2,9-positions was not achieved until very recently. In 2009, Kobayashi and coworkers first reported the Ir-catalyzed direct- diborylation of tetracene to produce 2,9- and 2,8-diboryltetracenes 19 and 20 respectively

12 (Scheme 1.4)."' Compounds 19 and 20 are building blocks for the regiospecific synthesis of extended ^-conjugated tetracenes, which are useful semiconductors for organic field effect transistors (OFETs). For example thiophene-tetracene-thiophene, thiophene- tetracene-bithiophene-tetracene-thiophene 21 and thiophene-tetracene-anthracene- tetracene-thiophene 22 with extended ^-systems are synthesized using 19 and 20.32 It should also be mentioned that tetracene-bithiophene-tetracene and anthracene- bithiophene-anthracene systems have already been reported as promising candidates for thin film transistor (TFT) applications.J The charge carrier mobilities of the highly stable tetracene-thiophene and anthracene-thiophene hybrids discussed above are as high as 0.5

~~9 9 o ii cm /Vs and 0.1 cm /Vs respectively, with on/off current ratios greater than 10 .~~

~~13 Si(!-Pr)2H i(i-Pr)2H~~

~~16 Si(i-Pr)2H n SiO-PrfeH~~

~~1 r-BuLi~~

~~2 (!-Pr)2HSiCl !r~~

~~\Suzuki / UP 67»X° Lx~~

~~R = 2,6-dnsopropyl R' = 4-(t-octyl)phenoxy yield, 53% R=n-C,,H Si(i-Pr)3~~

~~Scheme 1.4: Substituted tetracene compounds useful for electronic applications~~

14 There are also widespread applications of functionalized tetracenes which involve tetracene quinones as precursors. For example, rubrene (5,6,11,12-tetraphenyltetracene) and functionalized rubrene candidates with hole mobilities of up to 0.7 cm2/Vs are promising for OLED and FET applications.'4 Self-assembly of stable nano-fibers of 2,3- di-n-alkoxytetracene are expected to be useful for opto-electronics and semiconducting devices."^ Additionally, rhenium-based metallocyclic complexes of tetracene have been recently reported to form a molecular altitudinal rotor."6

~~1.1.1.5 Pentacene and Its Applications~~

Pentacene is a deep blue, crystalline material of high reactivity and sparing solubility in organic solvents. Its pink solution in organic solvents exhibits bright red fluorescence under UV light. The fluorescence quantum yield of pentacene is around 8%

(in cyclohexane) at 585 nm.37 Pentacene sublimes at high temperatures in a vacuum, and decomposes at temperatures over 300°C. Pentacene is unstable in solution phase. Dilute pink solution of pentacene in o-DCB or in CHCI3 decolorizes in a few minutes. Unlike anthracene, pentacene cannot be isolated from petroleum, hence it needs to be synthesized. Synthesis of pentacene was first accomplished through dehydrogenation of dihydropentacene by Clar in 1929/8 This involved two Friedel-Craft acylations of m- xylene with benzoyl chloride to prepare dibenzoyl-/w-xylene (a diketone). With further heating in the presence of copper, the diketone produced 6,13-dihydropentacene, which, upon dehydrogenation, yielded pentacene Scheme 1.5.

~~15 CI AICI3 Cu + Pyrolysis 2 equivalent~~

~~Phenanthraquinone » PhNOo~~

~~Scheme 1.5: The very first synthesis of pentacene by Clar. 38~~

The most common synthetic pathway to the large-scale synthesis of pentacene involves 6,13-pentacenequinone 23, easily synthesized by the aldol condensation of o- phthalaldehyde and 1,4-cyclohexanedione in an ethanol aqueous-base mixture (Scheme

1.6).39 Alternatively, 23 can also be synthesized by the reaction of a,a,a',a'-tetrabromo-o- xylene and benzoquinone in the presence of Nal (or KI) in DMF.40,41 The reduction of 23 with aluminum42 or aluminum/HgCl2 mixture43 in cyclohexanol yields pentacene

~~(Scheme 1.6). Because of the health and environmental risks involved in the use of mercury, Dehaen and coworkers recently demonstrated a new procedure to first~~

~~synthesize 6,13-dihydro-6,13-dihydroxypentacene 24 from 23 using L1AIH4 followed by a reduction using HCI/H2O to produce pentacene with an improved yield of 54%.44~~

~~However, an alternative milder method involves the synthesis of 24 using NaBH4, then a treatment of SnCLVHCl to produce pentacene in a quantitative yield (Scheme 1.6). '~~

~~16 O O Aq. KOH /WCHO NalorKI EtOH ^"CHO DMF (a) (b) 2 equivalent O O Br (d) LiAlH4/reflux 2 equivalent (cj\ Cyclohexanol or (e) NaBH4/RT> VA1, HgCl2 OH~~

~~(f) HCl/H2Q/reflux~~

~~or (g) SnCl2, HCl/dioxane/RT 24 OH~~

~~Scheme 1.6: Common methods to synthesize pentacene~~

~~1.1.1.5.1 FETs and Charge Carrier Mobility of Pentacene~~

Pentacene is a benchmark in the field of thin-film organic electronic devices due to its ^-conjugated electronic structure, a low HOMO-LUMO gap, strong two- dimensional electronic interactions in the solid state and ease of synthesis. Pentacene, having 7r-conjugation and high HOMO energy of -4.94 eV46 (calculated using B3LYP/6-

311+G**) exhibits electron-donating properties. It is the most common organic semiconductor used for p-type semiconductors in OTFT or OFET devices.4''48'49' There are two kinds of OFET device configurations, known as "top contact" (a) and "bottom contact" (b) structures (Figure 1.5).50'13 The semiconductor, i.e. the pentacene layer in both figures, represents the organic thin-film deposited on the gate insulator, i.e. generally an oxide layer covering the gate. This gate controls the voltage of the devices and thus the current from the source electrode to the drain electrode through a thin film of the semiconductor. Due to poor solubility of pentacene, high-vacuum deposition is the most common technique by which to make a thin film.51 In both "top contact" and 17 "bottom contact" devices, the morphology" and the crystallinity of pentacene in the solid state (and thus the electronic coupling among the individual molecules) is one of the most important factors affecting the electronic performance of the device.8'13 The preferred order of molecular orientation is the coplanar arrangement along the axes of the molecules to achieve a better overlap among the 7i-orbitals of adjacent molecules.!j This

7t-electron-rich "face-to-face" arrangement (c) enhances the electronic coupling in the n- stacking array (Figure 1.5).53 However, like all the other acenes, pentacene also adopts the classic "herringbone" arrangement (d), where one edge of the molecule is oriented toward the z-face or the flat plane of the other molecule (Figure 1.5). Thus "edge-to- face" arrangements dominate in the solid with two-dimensional electronic coupling.

Using the grazing incidence X-ray diffraction (GIXD) technique, it has been shown that the monolayer of the crystalline pentacene grown on amorphous Si02 (the most common gate insulator) also has a herringbone configuration. However, the lattice parameter of the monolayer and its crystal structure (e) differ from that of the (001) single-crystal of bulk pentacene (d) reported by Fritz and coworkers (Figure 1.5).54 This finding is important in understanding the pentacene gate-insulator-interface chemistry, which in turn greatly affects the mobility of a device, because carrier transport in pentacene OTFTs is believed to occur in the semiconductor layers near a dielectric interface.

~~18 Dtnu. Suutu: , r SJ: •,ivO!i!;ic:i: :uo. :-!'."jt Dials; S^ofcottdiictor mNif '.* ^ ' Gateiasulatof - ti.vo !•:•<•!!, \:i x §f;-," Gate.-, *< Gate |~~

~~Sill! • • Mbstrate MI^ ~ (a) Top contact (b) Bottom contact~~

~~(e) Energy-minimized monolayer (c) Face-to-face orientation (d) Herringbone: edge-to-face crystal structure of pentacene exhibits edge- structure of bulk pentacene. t0.face arrangements.~~

Figure 1.5: (a) and (b) represent two configurations of FET devices, (c) model face-to- face arrangement of pentacenes, (d) crystal structure of bulk pentacene,54 (e) model monolayer structure of pentacene,54 images (d) and (e) are reprinted ("in part") with permission from [54]. Copyright 2004 American Chemical Society.

It has been realized that the factors that can affect the charge transport mobility and device performance to a large extent include (1) the polymorphism character of pentacene;55 (2) the effect of purity of the pentacene deposited film on hole mobility;56

(3) grain size,3, grain boundary and defects of the pentacene film (which behave as traps for the charge carrier thereby decreasing the mobility);58^9 (4) the chemistry of the gate dielectric surface (which can affect the charge carrier mobility at the pentacene interface);60'61 (5) the chemistry of the interface between pentacene and the metal electrodes in terms of the difference of the work functions of the metals and the energy of the HOMO of the pentacene (where a mismatch of the energy difference results in

~~19 decreasing the hole injection barrier); and (6) the bias stress and stability of the pentacene devices.6'~~

~~In spite of these mitigating factors, the high charge-carrier-mobility of pentacene~~

~~FET devices remains comparable to that of amorphous silicon FET devices (~1.0~~

~~cm2/Vs). Since pentacene is a p-type semiconductor, device performance largely depends~~

on the hole mobility (jJ.hoie) of pentacene, which in turn depends on two main factors: (1) the electronic coupling (transfer integral) between adjacent molecules (which needs to be maximized) and (2) the reorganization energy X (which needs to be minimized for

~~efficient transport). Reorganization energy refers to the sum of the geometry relaxation~~

~~energies for the transition from the neutral-state geometry to the charged-state geometry~~

~~and vice versa.64 According to computations performed by Bredas and coworkers using~~

~~B3LYP/6-31G**, the reorganization energy of pentacene is very small (0.098 eV, -50%~~

~~of TIPS-pentacenes (c.f. Section 1.1.1.6.1). This explains the high hole-mobility of pentacene. Pentacene TFT devices with hole mobility as high as 2-5cm /Vs (using Si02~~

~~dielectric)65'66 and 6.4 cm2/Vs (using polymeric dielectric),6' and with typical on/off~~

~~current ratio as high as 10"6-10"7 were reported.51 Additionally, Palstra and coworkers reported improved purity of single-crystal pentacene by a repeated vapor-transport~~

~~crystallization method, thereby removing the major impurity, quinone 23, which can result from synthetic origins or the oxidation of pentacene. Using a space-charge-limited~~

~~current (SCLC) measurement technique, they found that the hole mobility of a purified~~

~~single-crystal of pentacene can be as high as 35 cm2/Vs56'5! at room temperature, which~~

~~can increase to 58 cm2/Vs at lower temperatures (225K) while maintaining the mobility~~

20 vs. temperature power law (p, ~ jT").68 Further, Palstra and coworkers used 23 as the gate insulator over a single-crystal pentacene layer in an FET device and achieved a high carrier-mobility (15-40 cm2/Vs) at room temperature.69

~~1.1.1.5.2 Recent Advances with Pentacene in Other Applications~~

Based on the generalized Shockley equation for p-n junctions that describes the dark current characteristics of organic hetero-structure barriers, Forrest and coworkers demonstrated a theoretical model which predicts that organic hetero-interfaces consisting of pentacene/C6o have high potential for solar cells (with PCE approaching 12% to

16%).70 The dipole interactions of pentacene/C6o aggregates, which tend to originate from a polarization effect at the pentacene-C6o interface, have been studied by complementary, microelectrostatic and quantum-chemical calculations.1 However, PCE over 2.7% has not been achieved yet in practice.7" As these remain less efficient compared to other organic and inorganic, including dye-sensitized, solar cells, efforts are being made to improve PCE and the stability of pentacene based solar cells.71

~~Extensive efforts have been carried out to integrate pentacene into OLED devices.~~

~~Shi and Ma studied the doping of pentacene in a hole injection layer, made of a 7V,/V-bis(l-~~

~~4 naphthyl)-AyV-diphenyl-l,l-biphenyl-4,4-diamine (NPB) film in an Alq3 based OLED.'~~

They found 1% pentacene-doping enhanced current efficiency from 3.9 cd/A to 5.1 cd/A, and higher maximum luminance from 13000 cd/m2 to 21000 cd/m2. In 2010, Rao and coworkers fabricated a green emitting OLED, using a "tandem" structure, consisting of a pure organic connecting unit of C6o/pentacene sandwiched between two identical 21 emissive units of NPB/Alq3. " Such tandem devices exhibit a 34% improvement in current efficiency relative to conventional devices.

The combination of pentacene with inorganic materials has further opened a new direction for novel applications. Vuillaume and coworkers demonstrated a "two-in-one" organic memory-OFET system consisting of gold nano particles incorporated at a pentacene-Si02 interface (Si02 being modified with an amino-terminated self-assembled monolayer).'6 In 2010, Im and coworkers fabricated a TFT based non-volatile flash memory with pentacene at the top layer for the gate hole injection and a ZnO layer for the electron channel.77 They also fabricated flexible semitransparent pentacene-NiO* based

TFTs.78 Armstrong and coworkers recently demonstrated a dual-beam sensor platform by using an OLED (as source) based on electroluminescence of Alq3/TPD as a heterojunction and organic photovoltaic (OPV) detectors based on pentacene/C6o as a planar heterojunction.79 Amrani and coworkers reported an optical coupling between the organic components of an Alq3 based OLED and a pentacene based OTFT on the same transparent substrate, to characterize the performance of organic photo-couplers and phototransistors.80

~~1.1.1.5.3 Drawbacks of Pentacene~~

Despite the potential as a candidate in electronic applications, pentacene has several limitations with respect to solubility and stability.13 Due to its poor solubility in common organic solvents at room temperature, applications involving spin-coated thin film flexible devices are difficult to design with pentacene. Also, even though pentacene 22 is easily synthesized (Scheme 1.6), the poor solubility of pentacene makes its purification more difficult. Therefore, commercially available pure pentacene is very expensive.

Apart from poor solubility, pentacene is prone to react with oxygen, and unlike tetracene it forms an irreversible photodimerized product in the presence of air and light at room temperature. There are essentially two solutions researchers have used to overcome this problem. The first one is to make thin films of soluble pentacene-precursors and then convert them to pentacene in an inert atmosphere with irradiation of light of a specific frequency (precursor route).81 Alternatively, one can synthesize completely new, soluble and stable functionalized pentacenes and then form the thin film. In the precursor route, the performance of the devices is not as high as those built from the conventional pentacene deposition route. In the second case however, the properties of the new functionalized pentacenes would be different than the parent pentacene. Thus the parameters and conditions affecting the design of the devices should be revised for each of the new cases separately.

~~1.1.1.6 Scope of Functionalized Pentacenes~~

The designing and the synthesis of a new class of materials with functionalized pentacenes is the alternative for pushing the field of pentacene based semiconductor devices to a new performance level. Although reactivity and instability of pentacene is higher than anthracene and tetracene (vide infra), it is again difficult to synthesize functionalized pentacenes directly from pentacene due to its poor solubility. The most common route to prepare functionalized pentacenes is by preparing 6,13- 23 pentacenequinone (23) or derivatives of 23. The corresponding pentacenequinones could then be reduced to the corresponding dihydroxy pentacene derivatives by attaching the desired functional groups via an organometallic 1,2 addition reaction (Scheme 1.7, path a). Alternatively, the 6,13-dihydroxy-6,13dihydropentacene 24 or derivatives of 24 could be synthesized via a substitution reaction (Scheme 1.7, path b). In the final step the corresponding functionalized pentacenes are formed by aromatization. Numerous substituted pentacenes (25-71) have been synthesized using these methods some of which are listed in Figure 1.6.

~~„ RLiorRMgX OH R K2 X=Br. CI , Ri~~

~~R2 Reduction RY and addition OH R (a)~~

~~R, Rj and R2 : Functinal groups~~

~~SF ^2 ZnI,/RSH H SR R2 Chloranil R, substitution ^R Aromatization R^ OH H R H SR~~

~~Scheme 1.7: Two common pathways (a and b) to synthesize functionalized pentacenes.~~

In 1942 Allen and Bell first synthesized the more stable and more soluble 6,13- diphenylpentacene 25 and 5,7,12,14-tetraphenyl-pentacene 88, compared to the parent pentacene.82 Since then, a wide variety of substituted pentacenes (25-71, Figure 1.6), with different functional groups, connected through 'C-C, 'C-X' (X = F, CI, Br), 'C-O' and 'C-S' bonds, have been synthesized. In the following, some of these functionalized pentacenes are considered to illustrate how functionalization influences device properties.

~~24 R:-S 3~~

28. R3= «Bu 33: R3= Si(;Pr)3 v.1 40. R5= CH3 29: R3= H-pentyl 34: R3= Si(;Pr)2Et 39 41: R5= (CH2)4CH3 30: R3= n-hextyl 35: R3= Si(iPr)2(n-Bu) M 25: R, = R2 = H 42- R5= (CH2)7CH3 31: R3= n-octyl 36: R3= Si(;Pr)2(.sec-Bu) 26 R,=H, R2 = «Pr 43: R5= (CH2)9CH3 32. R3= n-decyl 37: R3= Si(jPr)2(»-Hex) 27: Rx =H, R2 = rBu 44: R5= Ph 38: R3= Si(»Pr)2(»-Oct) r 45: R5= (CH2)2SiMe3

~~Si(*Pr)3 Si(iPr)3~~

Q Oyz 46: R= R[= R3= R4 = H, R2 = R5 = CH3 58 47: R,= R3= R4 = H, R2= Cl, R= o-dimethylphenyl Si(;Pr)3 Si(;Pr)3 48: R, = R2 = R4= R5 = H, R3 = Ph Si(;Pr)3 49: R, = R2 = R4 = R5 = F, R3 =H, R = CCSi((Pr)3 50: R, = R2 = F, R3 = R, = R5 = H, R = CCSi(iPr)3 51. R, = R2 = Cl, R3 = R, = R5 = H, R = CCSi(iPr)3 ) 52. R, = R3 = R4 = H, R2 = R5 = CN, R = CCSi(»Pr)3 53: R, = R3 = R4 = R5 = H, R2 = CN, R = CCSi(;Pr)3 59 54 R, = R3 = R4 = R5 = H, R2 = CN, R = CCSi(iBu)3 Si((Pr)3 55: R, = R3 = R4= Rs = H, R2 = CN, R = CCSi(cyclopentyl)3 56:R1 = R3 = R4=R5 = H,R2 = CN, R = CCSi(cyclohexyl)3 R

H,R=Ph (R,)3S,- "Si(Ri)3 CCSi(>Pr)3,R = OCH3 o 62: R, = CCSi(iPr)3, R = CH3 63:R!=CCSi(;Pr) ,R = H 3 67: R = R = H, R = CCSi(iPr) 64:R!=CCSi(iPr) ,R=Br 3 2 3 3 68: R= CCSi(cyclopentyl) , 3 69: R[ = I?T, R2 = H 65:R1=CCSi(;Pr)3,R = F R2 = H, R3 =CN 70: R! = n-hexyl, R = H 66:R1=CCSi(;Pr)3,R = CF3 2 71:R,=;Prik. rvj -tri, rs.R2 —= 011VICSiMe3 Figure 1.6: Symmetric and asymmetric functionalized pentacenes (25 - 71)

~~1.1.1.6.1 FETs or TFTs of Functionalized Pentacenes~~

Wudl, Bao, Bendikov and coworkers obtained a single crystal of 2,3,9,10- tetramethylpentacene 46 having a herringbone structure similar to the bare pentacene, except with an increased distance between the edges due to the presence of the methyl

~~h3 (CH3) groups. The highest temperature dependent mobility of the vapor deposited 46 was achieved up to 0.3 cm2/Vs at 85 °C (Table 1.2).~~

~~25 Pentacene 39 with 2-thienyl groups at its 6,13-positions has the preferred cofacial~~

7r-stacking arrangement in its crystal structure with a n-n distance of about 3.6 A.84 The hole mobility of 39 has been shown to be 0.1 cm2/Vs (Table 1.2). It is predicted that the absorbance of functionalized pentacenes depends on their state of matter. For example, the maximum absorbance wavelength (X^ax) of 39 has been reported to undergo a red shift from 604 nm to 677 nm, when transformed from its solution phase to a thin film solid state.

~~Similar 7i-stacking arrangements have also been reported for bis(triisopropylsilylethynyl)pentacenes (33 and 67).85 Pentacene 33, commonly known as~~

TIPS-pentacene, is reported to be a more stable and therefore a better potential candidate for TFT than unsubstituted pentacene. A group of similar pentacenes containing alkylethynyl (28-32) or alkyl(diisopropylsilylethynyl) groups (34-38) have been synthesized by Chen and coworkers. Based on differential scanning calorimetry (DSC) and electron diffraction experiments, it has been demonstrated that the Si-based pentacenes (34-38) have much higher thermal and chemical stability, and they are more crystalline than the non-Si-based pentacenes (28-32). All the alkylsilylethynyl pentacenes

(34-38) have a strong peak at 645 nm in THF which falls within ±1.88 eV of the optical band gap. Among the whole series of Si-based pentacenes (34-38) only 34-36 were found to be chemically stable upon solution casting and forming well-covered and textured thin films on silicon wafers. However, 33 is still claimed to have the best 7I-TT overlap in the crystal among all alkylsilylethynyl pentacenes, with a significantly smaller 71-71 distance of about 3.47 A (compared to the 6.27 A spacing between two nearest face-to-face

~~26 on j 1 0< unsubstituted pentacene molecules in the crystal). ' "' More interestingly, a better hole~~

2 88 mobility (phoie: 1-2 cm /Vs) with a high on/off current ratio (Table 1.2) was achieved when any of the standard solution deposition methods (e.g. spin coating, dip coating or drop casting) is used for the deposition of 33, as opposed to the vacuum deposition method (for the latter case, phoie: 0.4 cm /Vs).

~~According to Bao and coworkers, further fluoro- (49, 50) and chloro- functionalizations (51) of 33 can lower the band gap and decrease the 7t-7r distance to 3.36~~

A (for 5090) in the crystal packing, while retaining the face-to-face arrangement.91 In their thin film solid states, the tetra-chlorinated pentacene 51 has a lower band gap (Eg =1.61 eV, Table 1.2) than the tetra-fluorinated pentacene 50 (Eg = 1.66 eV) or the octa-

90 91 fluorinated pentacene 49 (Eg = 1.68 eV). ' This is because chlorinated pentacenes typically have a lower LUMO than their fluorinated counterparts due to the derealization of the 7r-electrons into the unoccupied 3d orbitals of chlorine, which are not available for fluorine.

The latest addition to the field of "functionalization-of-pentacene chemistry" is the substitution of pentacene with thio-alkyl or thio-aryl groups. In 2006, Kobayashi's group developed a synthetic approach to make alkylthio and arylthio pentacenes (40-42,

44 and 45).92 They demonstrated that 6,13-bis(methylthio)pentacene 40 acquires a preferred cofacial Tt-stacked packing arrangement in a 2D network sheet of crystals with a face-to-face pentacene-pentacene distance of 3.39 A. More recently, Miller and coworkers compared the stabilities and the HOMO-LUMO gaps of different new thio and non-thio substituted pentacenes.9"' This study demonstrates how the energy levels of

27 molecular orbitals of pentacenes can be affected by various substituents. The photooxidation stability trend, with the same concentration of all the compounds in DCM is: 6,13-bis(phenylthio)pentacene, 44 (Ua= 1140 min) > 6,13-bis(decylthio)pentacene, 43

~~(ti/2 = 750 min) > 2,3,9,10-tetrachloro-6,13-bis(2',6'-dimethyl-phenyl)pentacene, 47 (ti/2~~

= 620 min) > TIPS-pentacene, 33 (ti/2 = 520 min). Given their promising stability, pentacenes 40, 43, 44 and related heteroatomic substituted acenes are expected to perform well in a variety of organic electronic device applications.

~~Compound Technique Crystal Properties of TFT Ref Packing~~

~~46:2,3,9. lOtetramethyl-pentacene Vapor uMe:0.3at85°C deposition Herringbone On,'off:~10J XXCCCC Ref 84 CH-re:3.43A Eg(opt)=2.03eV. 39:6,13 -dithienyl-Pentacene Jt-Stack face-to-face On/off: ~104~~

~~Vapor transport 'S->nax= 604 nm crystallization s-7t:3.6A Xmax= 677 nm (thin Ref 85 film)~~

~~33:TIPS-Pentacene ;i-Stack 8 R Spin-coating face-to-face On/off: 10 Ref 86 >4.>ax=645nm ^F~^F^FF-F 7i-7t:3.47A Eg(opf)=1.81eV R R' = Si(fPr)3~~

50:1,2,3,4-Tetrafluoro-TlPS-Pent Jt-Stack uhok:0.111at60"C 3 R F Vacuum face-to-face On/off: 5xl0 Deposition ?W=654nm Ref: 91,92 3t-:t:3.36A ErtCV)=1.81eV R F E =1.66eV R:^5^Si(iPr)3 Table 1.2: FET properties and crystal packing structures of some selected functionalized pentacenes.

~~28 1.1.1.6.2 Other Applications of Functionalized Pentacenes~~

Aryl substituted pentacenes are well known for their potential in OLED applications. Some selected substituted pentacenes with their respective OLED properties are listed in Table 1.3. 6,13-diphenylpentacene 60 (Figure 1.6) was the first functionalized pentacene to be used to design a red emitting OLED.94 Later on, TIPS- pentacene-ethers95 (57, 58 and 59, Figure 1.6) were recognized as better candidates for

OLED applications. Only 25 mol% of 58 in Alq3 shows an enhanced performance in electroluminescence (EL) with a quantum efficiency (r)EL) of 3.3% and a maximum brightness of 3500 cd/m2 at 13V compared to that of aryl substituted pentacenes94'96 25 or

~~27 (Table 1.3). The properties of pentacene doped OLEDs are in good comparison with that of a standard non-doped Alq3 based OLED with maximum luminance of 15,800 cd/m2 at 22V (Table 1.3).97~~

~~29 Compound Procedure/i?e£ OLED Properties~~

25 Ph Vacuum ^=610 nm.. 1^^ = 600 nm, (CHC13), Deposition A.cm= 609 nm, A.max(abs) = 599nm, (toluene), A. = 625 nm (Red emmission) Ph cmOLED Ref 97 r)EL=1.3% . 0.55 mol% dopant in Alq3 U 27 JP Vacuum Xem = 618 nm, >W(abs) = 603 nm (CHC13), Deposition Xem= 613 nm, X,nax(abs) = 601nm, (toluene), WOLID= 625 run. Ref: 98 Max. luminance >3 000 cd/m3 at 17 V. nEL=l .4% . 0.47 mol % dopant in Alq3

~~rBu~~

58 i>i(iPr) 3 Vacuum Xem= 625—630nm (toluene), 1 Deposition >-an,OLED=650nm, Max. luminance=3500cd/m2at 12.75 V, Ref: 96 %L=3.3%,25mol% dopantinAlq3 11 ,i(/Pr), AH gp Vacuum km = 520 nm 3 Deposition kmfQLm"5l9nm, Max. luminance =15800cd/m2at22 V Ref: 99 Table 1.3: OLED properties of some selected functionalized pentacenes and Alq3.

~~Certain substituted pentacenes also show promising photovoltaic characteristics.~~

~~Lim and coworkers synthesized several new cyano-functionalized pentacenes (52-56 and~~

~~68) and studied the electron withdrawing effects of nitrile (-CN) group on them.98~~

Insertion of the nitrile group converts trialkylsilyl functionalized pentacenes to n-type pentacenes which act as electron acceptors in solar cells. A blend of poly(3- hexylthiophene) (P3HT) as a donor and pentacene 55 as an acceptor exhibits a PCE up to

0.43% under illumination of 100 mWcm"2 with an air mass 1.5 (AM 1.5). Nuckolls and coworkers however reported a much higher PCE (up to 1.4%) with a simpler device composition with fullerene as the n-type acceptor and dithienyl pentacene 39 as the p-

~~30 type donor."' This result is comparable to the solar cells made of fullerene and the parent pentacene, typically having a PCE of 1 -1.6%.!l~~

~~Recently, substituted pentacenes have been used in various modern applications.~~

Among these are FET of a single crystal of 33 for nonvolatile ferroelectric memory devices,100 polarized pentacenes 60-66101 (Figure 1.6) for conductive polarized spacer, dimers of pentacenes 69-71102 (Figure 1.6) for photoconductive optoelectronic materials and a stable nano-composite material made of 6,13-bis(4-propylphenyl)pentacene 26 and

~~103 Ti02 with very low band gap (-1.14 eV).~~

~~1.1.1.7 Larger Acenes~~

Larger acenes such as hexacene and heptacene are hardly found in natural sources. They neither occur in petroleum deposits (unlike anthracene or tetracene) nor in diesel exhaust or charred food (unlike tetracene and pentacene). However, there is evidence of them in volcanic ash and interstellar dust,13 although there is no evidence for acenes larger than heptacene. Theoretical predictions indicate that the band gap and the reorganization energy are inversely proportional to the size of the acene rings (section

1.1.2.4). Therefore, the charge carrier mobility increases with an increase in acene length.Ij Larger acenes are thus highly desirable for organic electronic applications. They are however difficult to synthesize, isolate and characterize due to their low solubility and extremely low stability.

~~31 1.1.1.7.1 Hexacene~~

~~The initial evidence of hexacene was provided by Clar104 and Marschalk103 in~~

1939 using two different synthetic routes, while more direct syntheses were later reported by Bailey and Satchell. In all these cases however, extensive characterization of hexacene could not be performed. Recently in 2007, Neckers and coworkers first isolated and synthesized hexacene both in a solution of toluene and in a solid matrix of PMMA polymer.108 Their synthetic procedure of hexacene involves a Strating-Zwanenberg photodecarbonylation of 6,15-dihydro-6,15-ethano-hexacene-17,18-dione by irradiation of light of 395 nm wavelength, in both the solution and the polymer matrix (Scheme

1.8). Hexacene was found to be very unstable in the solution due to a formation of its oxygen adduct and its dimer, as characterized by a MALDI-MS analysis. In the polymer matrix however, hexacene was stable for more than twelve hours in ambient conditions.

~~In this method hexacene was well characterized using NMR, UV and MALDI-MS for the first time. F(~~

~~Scheme 1.8: Synthesis of Hexacene.108~~

~~1.1.1.7.2 Functionalized Hexacenes~~

The crystal structure of the first ever functionalized hexacene 6,15-tri-tert- butylsilylethynylhexacene 72 (Figure 1.7) has been resolved. The crystal packing of 72 has a two dimensional 7i-stacking arrangement.109 Hexacene 72 was well characterized by 32 NMR in CDCI3 and UV-Vis in DCM. The electrochemical HOMO-LUMO gap of 72 is

1.58 eV and that derived from absorption spectra is 1.57 eV. These are in quite good agreement with the theoretical prediction of a lower HOMO-LUMO gap than that of pentacenes.93 Recently, four more similar silylethynyl substituted hexacenes 73-76

~~(Figure 1.7) have also been reported with similar 71-stacking crystal packing arrangements.110 The half lives (ti/2) of these functionalized hexacenes are in the range of~~

~~19-93 min in toluene. Photodimerization has been reported to be the most common decomposition pathway for these functionalized hexacenes.110~~

~~73:R = zBu . . 74: R = cyclopentyl I I -Si- 75: R = cyclohexyl §jj^ T-> 3 76: R = SiMe3 Figure 1.7: Molecular structure of substituted hexacenes.109'no~~

~~1.1.1.7.3 Heptacene~~

Heptacene was first synthesized by Clar111 in 1942. Alternate syntheses were reported later by Marschalk112 and Bailey.106 However, these synthetic approaches could not be easily reproduced which is likely due to the high reactivity and low solubility of heptacene.1 Moreover, such reports of the isolation of heptacene were based on a limited

33 set of characterization techniques. Recently in 2006, Neckers and coworkers synthesized and isolated the parent heptacene in a PMMA polymer matrix in a way similar to the hexacene isolation described above. Isolated heptacene was stable in the PMMA matrix for four hours only. Furthermore, it has no stability in the solution phase unlike hexacene.

To synthesize heptacene, Neckers and coworkers used a Strating-Zwanenburg photodecarbonylation of 7,16-dihydro-7,16-ethanoheptacene-19,20-dione, which was in turn prepared from 2,3-dibromonaphthalene in five steps in 18% yield (Scheme 1.9).

~~Scheme 1.9: Photochemical synthesis of heptacene, isolated in PMMA matrix.~~

A comparative study of the synthesis, stability and photochemistry of pentacene, hexacene and heptacene has also been recently performed by Necker and coworkers.114 In this study, all three parent acenes were prepared using the Strating-Zwanenburg photodecarbonylation of their corresponding 'dione' precursors, irradiated at 395 nm in solid inert gas matrices (e.g. argon) at cryogenic temperatures. The comparative absorption spectra of pentacene, hexacene and heptacene at 10K showed a red shift of

~~Xmax with the increase of the acene length (Figure 1.8).~~

34 Figure 1.8: Comparison of the electronic absorption spectra of the acenes obtained from their corresponding photoprecursors in argon matrices at 10 K. Reprinted with permission from [114]. Copyright 2009 American Chemical Society.

~~1.1.1.7.4 Functionalized Heptacenes~~

~~In 2005, Anthony and coworkers first reported two silylethynyl derivatives of heptacene 77 and 78 (Figure 1.9) along with hexacene 72.109 Unlike the TIPS-pentacene~~

33 (with three isopropyl groups attached to Si), neither TIPS-hexacene nor TIPS- heptacene were stable enough for isolation. However, hexacene 72 with tert-buty\ groups attached to Si was sufficiently stable for isolation and characterization. Similarly, unlike the hexacene derivative 72, heptacene 77 with tert-buty\ groups attached to Si, was sparingly soluble and marginally stable for characterization. On the other hand, heptacene

~~78 with three -SiMe3 groups attached to Si was more stable and soluble to allow for~~

~~1 1 % characterization by H and C NMR, UV-Vis, electro chemistry and X-ray crystallography. The HOMO-LUMO gap for 78 is as low as 1.36 eV (optical) and 1.30eV~~

~~(electro chemical). 35 77: R = 79:R=Ph 80: R = 78: R = Si(SiMe3)3~~

~~81: R= —=—Si(iPr)3~~

~~Ri = H 82: R=~~

~~H3C H3C~~

~~85: R= Ri 83: R= CH, CH3~~

~~Figure 1.9: Structure of functionalized heptacenes.~~

~~In 2008, Wudl and coworkers reported three more functionalized heptacenes 79,~~

80 and 81 (Figure 1.9). l3 Heptacene 81, stabilized by Si(z'Pr)3 was quite stable and could be characterized by NMR, UV-Vis, electrochemistry and X-ray crystallography. This heptacene is stable for over 24 hours in a degassed, capped NMR tube. The NIR absorption wavelength of 81 is approximately 20 nm red shifted than those of 79 and 80.

This shift is affected by the presence of the electron withdrawing TIPS-acetylene groups attached to the acene backbone of 81 (Figure 1.9). The HOMO-LUMO gap of 81 is 1.38 eV (electro chemical) and 1.35 eV (optical from onset of 917 nm) and the crystal structure shows a herringbone packing motif.

36 Employing a combination of electronic and steric stability, Miller and coworkers reported four more functionalized heptacenes 82-85 including two thio-substituted heptacenes (Figure 1.9).116 These heptacenes were sufficiently stable to be well characterized by NMR, UV-Vis and mass-spectral analysis. The photooxidative resistance of these heptacenes shows a trend (82 < 83 < 84 < 85). This explains that the effects of both the /?-(/-butyl)-thiophenyl group and the o, o '-dimethylphenyl group are responsible for an increase in the stability of the heptacenes. The />-(£-butyl)-thiophenyl group acts as an electron withdrawing group because of the presence of thio-substituents, and the o,o '-dimethylphenyl group provides steric hindrance to the heptacene backbone.

~~The maximum absorbance of heptacene derivative 85 is 865nm. Among 82-85, heptacene~~

85 is the most persistent acene which is stable for weeks in a solid phase and for 1-2 days in solution. The optical HOMO-LUMO gap of 85 is 1.37 eV which is comparable to those of the above mentioned heptacenes. Based on their lower band gaps, higher stabilities and enhanced solubilities, heptacenes 78, 81 and 85 are expected to be competitive candidates for TFT devices.

~~1.1.1.7.5 Octacene, Nonacene and Functionalized Nonacenes~~

Parent octacene and nonacene were recently isolated in an Ar-matrix117 using cryogenic matrix-isolation techniques similar to the procedure used by Necker's group to isolate hexaceneHJ8,U4 and heptacene113'114 as described above. Furthermore, there is no evidence for functionalized octacenes in the literature. Kaur and coworkers recently reported the successful synthesis, isolation and characterization of the first ever persistent 37 functionalized nonacene 86 and another less stabilized nonacene derivative 87 (Figure

1.10).]18 Nonacenes 86 and 87 were well characterized by lK NMR, mass spectrometry and UV-VIS spectroscopy. Both nonacenes 86 and 87 showed a blood-red fluorescence in solution under UV irradiation. In the solid phase 86 was stable up to six weeks and in solution up to 24 hours when protected from light and air. The optical HOMO-LUMO

1 i o gap of 86 is 1.12 eV which is in good agreement with the theoretical prediction and confirms the expectation of a decreased Eg(opt) compared to heptacene 85 (Eg(0pt) = 1.37 eV). These experimental results are in excellent agreement with the theoretical predictions based on the earlier synthesis of sulfur-stabilized pentacenes. ~ It has also been predicted that steric effects, electronic effects and positional locations of substituents are all important factors in controlling the photooxidative stability and band gaps of larger acenes. m

~~Figure 1.10: Structures of nonacene derivatives.~~

~~38 1.1.2 Theory behind Chemistry and Electronic Properties of Acenes~~

~~1.1.2.1 Stability and Reactivity of Acenes~~

The representation of benzene as two hybrid resonating structures (Figure 1.11), first proposed by August Kekule in 1865, was a major breakthrough in organic chemistry and may be summarized by a single structure depicted as a hexagon with a circle in the middle (Figure 1.11 (c)).120 The stabilization energy that originates from the aromatic interaction of Kekule's two canonical structures is known as the resonance energy in VB theory. ' According to Clar, the circle represents an 'aromatic sextet' for the benzene ring and may only be used to describe six pi-electrons and therefore cannot be used for all the benzenoid rings in acenes or more generally in PAHs (Figure 1.11

(d)). This is "because if the sextet is shared among more rings then the benzene-like character is diluted to such an extent that rather unstable systems are formed which nevertheless are aromatic".1'121 Thus Clar proposed that only one ring in a given acene can have one aromatic sextet (e.g. anthracene in Figure 1.11 (e)). This explanation by

~~Clar further clarifies the increased reactivity and the decreased stability of larger acenes.~~

~~Benzene~~

Figure 1.11: (a) and (b) Kekule's canonical structures of benzene; (c) resonance structure of benzene in VB theory; (d) incorrect representation of anthracene; (e) Clar's sextet representation of anthracene.

~~39 1.1.2.2 Comparative Study of Reactivity of Acenes~~

Biermarm and Schmidt studied the Diels-Alder reactivity of various PAHs towards maleic anhydride.122 The reported rate constants and relative reactivity of acenes are shown in Table 1.4. This result supports Clar's prediction of increasing reactivity of acenes with the increase in the number of rings. However, the increase in reactivity from pentacene to hexacene (~2 fold) is not as great as that from anthracene to tetracene (~20 fold) or that from tetracene to pentacene (~35 fold). In other words, the relative reactivity

(anthracene to hexacene) does not change linearly, suggesting a limit to the reactivity of the higher acenes. All these studies suggest that the center ring(s) of the acenes have both greater aromatic character as well as higher reactivity towards dienophiles in a 4+2 cyclization. These results also imply that the four carbons in the inner ring are electron- deficient. Hence addition of dienophiles at the inner ring stabilizes the ring and reduces the electron deficiency of the corresponding meso-carbons 123

~~Acene Rateconstan^lO*^) Normalized (10%)/2270~~

~~2270 2270 ^^^jy-^f 1 94200 47100 20.74 1 640 000 1 640 000 722.46~~

~~6 570 000 3285000 1447.13~~

~~Table 1.4: The Diels-Alder rate constant and relative reactivity of acenes~~

~~40 1.1.2.3 Photodegradation of Acenes~~

Photooxidation and photodimerization are the principal processes that lead to acene degradation. Comparatively, photooxidation is considered to be the more significant degradation path. In the presence of light and oxygen, acenes decompose into two main by-products such as the highly stable acene-quinones and the acene endoperoxide derivatives.124 Reddy and Bendikov's recent study regarding the energy states of possible intermediates of photooxidation of acenes explains that there might be two different paths for the photooxidation of acenes.125 The endoperoxide can either form by a reaction of the acene with singlet oxygen in a concerted fashion or with triplet oxygen in a stepwise, radical mechanism. In any case, the energy barrier for oxidation decreases with an increase in the ring number of the acene. The resulting endoperoxide then converts into the respective acene quinone (Scheme 1.10).

~~Scheme 1.10: Photooxidation of acenes in two different pathways, namely concerted and stepwise.~~

~~Attempts are being made to slow down the photooxidation thereby increasing the stability of pentacenes. Miller and coworkers studied the stability of acenes with respect~~

~~41 to their oxidation potentials in relation to higher HOMO energies vs. lower LUMO~~

~~energies.93 The experimental HOMO, LUMO values support their argument based on~~

~~their theoretical results. Due to the inductive effect of 2,3,9,10-tetrachloro substitution,~~

~~pentacene 47 (Figure 1.6) is either less dienophilic toward *02 (i.e., reduced HOMO~~

~~energy) or less prone to carry out a photoexcited electron transfer with triplet oxygen, 302~~

~~(i.e., reduced LUMO energy). They have also demonstrated that thio-aryl or thio-alkyl~~

~~substituted pentacenes possess enhanced photo-oxidative stability. They applied the same~~

~~theory of photooxidation stability by introducing 'thio' groups to synthesize~~

~~functionalized heptacenes116 and nonacene derivatives.118~~

~~Photodimerization is another less common degradation path of acenes. Smaller~~

~~acenes photodimerize much faster than larger acenes, that is possibly because the~~

~~photooxidation is much faster for the latter. An anthracene molecule, in its singlet excited~~

~~state, can attach to the center ring of another anthracene molecule in its ground state to~~

~~form the photodimerized adduct (Figure 1.12 (a)).126 Tetracene can also be dimerized~~

~~easily in the solution phase and has been reported as the major photodecomposition~~

~~product.127 Unlike pentacene, the colorless "butterfly" photodimers of tetracene (Figure~~

~~1.12 (b)), upon heating, can be converted to tetracene monomers in solution at room~~

~~temperature. Photodimerization products dominate in a deoxygenated environment. In the~~

~~case of pentacene, "butterfly" dimers (Figure 1.12 (c)) can be prepared via a photoirradiation of pentacene (X>440 nm) at 120 °C in deoxygenated 1-~~

~~chloronaphthalene. The pentacene dimer can be reversed back to the pentacene by a~~

~~photolysis reaction under UV irradiation for 30 minutes.128 Coppo and coworkers studied~~

42 the photochemistry of pentacene 33 and found an intermolecular 4+4 cycloaddition as the main photo-degradation product. " Similarly, Anthony and coworkers found that the photodimer is the major product in the photodegradation of silyl ethyl substituted hexacene.110

~~Figure 1.12: Photodimerized "butterfly" product of (a) anthracene, (b) tetracene and (c) pentacene.~~

~~1.1.2.4 HOMO-LUMO Energy and Band Gap of Acenes~~

Organic single crystals are important in studying the physical properties of organic compounds. However, due to their poor mechanical properties, they are not useful enough in technical electronic applications. On the other hand, organic thin films with highly ordered structures are good candidates for organic electronics.47 The intimate interrelations between high structural order and efficiency of charge transport or charge mobility of organic thin films vary with the choice of different film deposition parameters

(Section 1.1.1.5.1). Nevertheless, the band gap of organic semiconductors is directly related to the intermolecular interactions in their solid state thin films, and the values of the HOMO-LUMO energies of the individual molecules.130 In the case of organic semiconductors, the valence band (VB) is comprised of filled molecular orbitals while the conduction band (CB) is comprised of empty molecular orbitals. The schematic 43 representation of the interrelation between the band gap, the VB and the CB of stacked molecules as well as the HOMO-LUMO gap, the HOMO, and the LUMO of a single

~~(ethylene) molecule with cofacial orbital arrangement is shown in Figure 1.13. The~~

~~electronic behavior of organic semiconducting materials, including electron acceptor or~~

~~donor character, depends on the energy of the HOMO, the LUMO and their orbital~~

~~interactions. Molecules with a low HOMO-LUMO gap are desirable for use in organic~~

~~electronic devices because they provide materials with lower band gaps (i.e. more metallic-like) which have higher mobilities and therefore more desirable I/V profiles.130~~

This HOMO-LUMO gap can be tuned with the inclusion of different functional groups to the parent organic molecule which enables control over device properties. The charge transport mechanism can be explained by the semi-classical theory of the rate (kET) of

electron-transfer (hopping) from the charged molecules to the neighboring neutral molecules, shown in equation in Figure 1.13, where T is the temperature, X is the reorganization energy, t is the transfer integral, and h and kB are the Planck and

~~Boltzmann constants respectively. The transfer integral, t depends on the interaction of~~

~~two adjacent organic molecules.131 The reorganization energy is the sum of the relaxation~~

~~energies for the transition from the neutral-state geometry to the charged-state geometry~~

~~and vice versa.64~~

44 Figure 1.13: Illustration of bonding antibonding interrelation between the HOMO- LUMO levels of two ethylene molecules in a cofacial configuration and the formation of valence and conduction bands when a large number of stacked molecules interact (top); Semi-classical charge transfer theory shown in equation (bottom).131

Acene molecules (anthracene to pentacene) show promising semiconducting properties with lower HOMO-LUMO gaps (vide supra). Oligoacenes are a basic building block of graphite or CNTs. Hence understanding of electronic structure of acenes should be important for understanding the electronic properties of graphite and CNTs.130 As was already mentioned earlier, the higher the number of fused rings in acene molecules, the lower the HOMO-LUMO gap, the lower the reorganization energy and the higher the carrier mobility among the acene molecules.13'1"2 For instance large polyacenes were predicted to be like one dimensional organic conductors with zero band-gaps similar to graphite.130'133

However, many controversies and confusions still remain about the electronic structures, stability, aromaticity, and, most importantly, band gap (or HOMO-LUMO gap) of oligoacenes and polyacenes.!'4 Over the past decades, the insufficient information regarding instability and the actual electronic state of higher acenes has drawn strong

45 attention of theoretical chemists. According to Houk and coworkers polyacenes (acenes longer than octacene) are two fully delocalized non-alternating ribbons joined by relatively long bonds, having smaller band gaps than the corresponding polyenes and being in triplet ground states.1'5 Recently this conclusion has been modified by Bendikov and coworkers who claimed that an unrestricted broken symmetry wave function

(UB3LYP) of density functional theory (DFT) is necessary to understand the electronic states of higher acenes.136 Their unrestricted open shell calculation discovered that oligoacenes larger than hexacene have an open-shell singlet ground state (where the triplet lies above the singlet) with a diradical character demonstrated by an increasing spin contamination . The two singly occupied molecular orbitals (SOMO) of decacene, which are essentially localized on the two ribbons, are shown in Figure 1.14

(a) (for comparison, the HOMO and LUMO of pentacene, which is a closed shell singlet having nonradical character, are also shown in Figure 1.14 (b)).! j6 This prediction is very important to guide chemists in synthesizing larger acenes with greater stability. For instance, Miller and coworkers demonstrated that the value and the diradical character of nonacene can be controlled by using selective functional groups as well as by their positional arrangements on the nonacene backbone. ' In fact the value was shown to be zero for some particular cases, which exactly suites their experimental results of synthesizing the corresponding functionalized nonacenes. This experimental evidence of nonacene is in agreement with previous theoretical predictions of electronic structures for higher acenes. Some more recent theoretical studies by Hachmann and coworkers13, and Jiang and coworkers1"8 involving high-level wave function theory using

46 a new ab initio density matrix renormalization group (DMRG) algorithm and first principles spin-polarized theory (DFT) methods, also showed a similar prediction for electronic structures for higher acenes (with varying number of fused benzene ring, n up to 40). However, their studies suggested refining the inaccurate "diradical character" term resulting from DFT calculations which substantially underestimates the singlet-triplet gap of acenes larger than decacene. According to their prediction, the ground state of larger acenes has singlet polyradical character and the number of unpaired electrons increases with the size of the acene which therefore possesses antiferromagnetic character in its ground state.136'137 The edge localized magnetization for the spin-up and spin-down electrons increases with the size of the acene and hence the antiferromagnetic state of longer acenes will have more than two unpaired electrons, and will not necessarily have a diradical character.

~~# W *l * # W # 'w >*** 0 r „ <• 7 *i •; 0 K V~~

~~o '^ ^ .-._ N >j O'* c *'~~

a b Figure 1.14: (a) Singly occupied orbitals of decacene (UB3LYP/6-31G(d)). Reprinted with permission from [136]. Copyright 2004 American Chemical Society, (b) Molecular orbitals, HOMO and LUMO of pentacene (DMRG). Reprinted 'in part' with permission from [137]. Copyright 2007 American Chemical Society.

~~41 1.2 RESULTS AND DISCUSSION~~

~~1.2.1 Sulfur Stabilized Pentacene Derivatives~~

~~1.2.1.1 Synthesis of 3,3'-(Pentacene-6,13-diylbis(sulfanediylY)dipropanoic acid,~~

~~an Intermediate for Making A Molecular Switch~~

Pentacene-like, conjugated, carbon-based materials are light weight with high mechanical flexibility and are easily processable into electronic devices.lj9 In principle, these materials could be used to fabricate integrated circuits, where, for instance, each transistor is made from a single crystal of pentacene. Introducing specific chemical groups to the pentacene molecule, such that the oxidized and reduced states of the modified molecule have different conductivity properties140 would allow for each functionalized pentacene to behave as a molecular switch. We propose to make a molecular switch based on our knowledge of sulfur stabilized pentacenes (Section

~~1.1.1.6.1). The rearrangement of the proposed functionalized pentacene into two different states (ON and OFF) by means of an electrochemical-chemical (EC) mechanism141 is shown in Figure 1.15.~~

~~Figure 1.15: Pentacene based molecular switch based on EC mechanism. 48 1.2.1.1.1 Synthesis~~

~~The ON-state molecule in Figure 1.15 is the salt of 3,3'-(pentacene-6,13- diylbis(sulfanediyl))dipropanoic acid 88. The synthesis of 88 is shown in Scheme 1.11.~~

~~O HCK/H NaBH,~~

~~\^CH0 10%NaOH,' MeOH or THF EtOH, 17h RT, 17h, 93% HO H RT, (95%) 24~~

~~HOOC^^ HOOC^/^ Znl2, HS(CH2)2C02H Chloranil DCM, RT, 17h K C0 , 60 °C (81%) 2 3 Benzene HOOC COOH 89 88~~

~~Scheme 1.11: Synthetic scheme of pentacene 88.~~

6,13-Pentacenequinone, 23, was prepared in 95% yield by an aldol condensation between o-phthalaldehyde and 1,4-cyclohexanedione following a similar procedure as described in Section 1.1.1.5, except that NaOH was used instead of KOH/

~~In the next step, 6,13-dihydroxy-6,13-dihydropentacene 24 (a white solid) was~~

~~92 prepared by reducing 23 using NaBH4 in MeOH, adapting Kobayashi's procedure.~~

~~Compound 24 could also be synthesized using wet THF following a modification of~~

~~I A^~~

Zeynizadeh's procedure. " In the second case, however, there was evidence of two isomers of 24 being formed, and upon washing with cold CHCI3 one isomer is isolated in greater than 90%> yield. No experiment has been performed to clarify which isomer is the major among the cis and the trans 24. Both isomers are reactive in the following step. So 49 in most of the cases, crude and dry 24 was used for further reaction.

Compound 24 was then treated with two equivalents of ZnJ-2 and 3-thiopropanoic acid in dry DCM to produce 3,3'-(6,13-dihydropentacene-6,13- diyl)bis(sulfanediyl)dipropanoic acid 89 following the reported procedures to synthesize other dihydrodithiopentacenes.92,93 The reaction required a longer time than the two hours as previously reported. Upon overnight stirring, a pinkish white precipitate came out of the solution which was then filtered and rinsed thoroughly with DCM followed by water to get rid of the excess starting materials. The NMR spectral data of the recovered white solid confirmed the existence of only one isomer (either cis or trans) of 89. However, in a few other batches, the DCM filtrate contained both isomers of 89. The major product of this reaction was obtained as a white solid residue in 81% yield. The solid from the filtrate portion also contained 15%o of the major isomer of 89 (calculated based on NMR integration). No experiment was performed to check whether the cis or the trans isomer was the major product. Nevertheless, the major isomer of 89 was used for further reaction. The thermogravimetric analysis (TGA) of 89 confirmed that it is stable up to

175 °C with major weight loss started after 260 °C. Due to two acid groups present in the molecule, 89 has low solubility in non-polar organic solvents such as DCM or CHCI3, but it is highly soluble in polar organic solvents such as acetone, MeOH and DMSO.

~~Initially, oxidation of 89 to 88 was attempted by using chloranil and K2C03 in benzene at 60 °C in the dark, as reported by Kobayashi92 and Kaur93 (Scheme 1.11).~~

~~However, after overnight stirring, some insoluble black solid was recovered. The reaction failed possibly due to the poor solubility of 89 in non-polar solvents like benzene.~~

50 Therefore we considered using polar solvents as well as different procedures and/or conditions for aromatization. Chloranil,92,93 o-chloranil, IBX14"' and triphenylmethyl perchlorate (TPP)'45 are known reagents to effect dehydrogenation and aromatization.

~~These reagents were used to aromatize 89 in various solvents (e.g. benzene, acetone,~~

~~CHCI3, DMSO etc.), with varying temperature and time, in the dark and inert gas atmosphere. Some of the important and recurring observations are summarized in Table~~

~~1.5. In most of the cases, either an insoluble black solid or the starting material (SM) was recovered. Only in three cases using (c) chloranil and K2C03 in dry acetone, (d) IBX in~~

~~DMSO and (e) TPP in acetic acid, a blue solid along with SM was recovered (Table 1.5).~~

Since the expected product 88 and the SM 89 are both highly polar compounds, it was impossible to monitor the reactions using TLC. As all the reported pentacenes are dark- blue in their solid state and either blue or purple in solution, the reactions were monitored based on the appearance of blue coloration.

~~Obs. Reagents/solvents Reaction Results conditions~~

~~00 Chloranil, K2C03/ 60°C/2d/Ar Black solid dry Benzene /dark~~

(b) o-ChlorariiLK2CCy 60°C/2d/Ar SM 89, dry Acetone /dark PQ 23 (c) Chloranil, KXOj/ 60oC/17h'Ar Blue solid, dry Acetone •'dark SM 89 (d) IBX/DMSO 60°C/17h/Ar Blue solid, /dark SM 89 (e) TPP/ Acetic acid Rellux/40min/ Blue solid, Ar'dark SM 89 Table 1.5: List of observations for the attempted aromatization of 89.

~~In all three cases of (c), (d) and (e), starting material was detected even after~~

~~51 thorough washing with different solvents (CHC13, DCM, hexane). A chromatographic~~

~~separation with a small silica column was thus performed to isolate the product with blue~~

~~color. The polarity of the solvent was varied by changing the relative concentrations of~~

~~DCM and MeOH. Finally, the blue fraction was collected separately in MeOH. The UV~~

~~spectra of the blue fractions for each of the three cases have shown expected vibronic~~

~~characteristics at long wavelengths around 500-650 nm with Xmax at 611 nm in MeOH~~

~~(Figure 1.16). The A^ax matches with those of known thio-substituted pentacene~~

~~derivatives reported in the literature.93 However, after the evaporation of the solvent, the resulting blue solid had a low solubility in MeOH while almost no solubility in DCM or~~

~~CHCI3. This is possibly because the expected product is highly polar. Hence, the proton~~

~~NMR of the recovered blue solid was performed in deuterated MeOH (CD3OD), which~~

~~exhibited one up-field triplet corresponding to one methylene proton at 2.42 ppm (Figure~~

~~1.16). Another triplet corresponding to the second methylene was believed to be buried under the solvent peak. In the aromatic region, there were two multiplets at 8.08 ppm and~~

~~8.00 ppm (AA'MM' pattern) and one singlet at 9.64 ppm. These NMR studies indicated~~

~~that the blue band contained the desired product. There were three more multiplets and~~

~~two more singlets, which, however, corresponded to some unknown impurities that could~~

~~not be assigned. All these peaks were shifted compared to that of the starting material 89~~

~~in MeOH (Figure 1.16). The mass spectrum of the blue solid revealed the molecular ion~~

~~peak with low intensity and fragmentation peaks with higher intensity (see appendix).~~

~~52 \ 88~~

~~UV-Vis spectra in MeOH Wavelength (nm)~~

~~H,0 MeOH~~

~~88 •i w»i»i»<>>iWwMM#»'»»>we^«SM<** ***** LJU 5 4 % W»~~

~~H20~~

~~89 MeOH~~

~~J L , I J v»_ ,~~

~~Figure 1.16: UV-Vis spectra, NMR spectra of 88 in MeOH and CD3OD at top and NMR spectra of 89 in CD3OD at bottom with expected peaks for 88 marked with the asterisks.~~

Based on the observations discussed above, we assumed that we were able to synthesize 88. However, the yield of the reaction was very low and a large scale reaction was never tried. In order to synthesize the ON state molecule (Figure 1.15) for the molecular switch, bulk amounts of compound 88 are needed. The electrochemistry of salts of pentacene 88 are needed for future work.

~~53 1.2.1.2 Synthesis of S,S,-Pentacene-6,13-diyl diethanethioate, an Intermediate~~

~~for Making Pentacene Oligomers with Disulfide Linkages~~

~~In Section 1.1.1.5.1 it has already been discussed that pentacene forms a~~

~~herringbone arrangement in the solid state. There are also examples where functionalized~~

~~pentacenes have preferred face-to-face arrangements in the solid state (Section 1.1.1.6.1).~~

~~It would thus be useful if one could control the morphology of a thin film of pentacene in~~

~~its solid state. One way to control the morphology would be to chemically force the pentacenes into aligning themselves in a particular direction in a one dimensional array~~

~~during a deposition method. This might help to get them further organized into two~~

~~dimensional arrangements in a solid state thin film. In this current project we have~~

~~proposed to synthesize 6,13-pentacene thiol 90 which could potentially form a pentacene~~

~~oligomer through a di-sulfide linkage (Scheme 1.12). This particular oligomer would have two important attributes for producing a better quality thin film of pentacene. First,~~

~~the end thiol functional group would help to self-assemble on a metal surface through~~

~~sulfur-metal chemical bonds and second, the di-sulfide linkage would control the~~

~~pentacene backbone to be oriented in a particular direction to achieve better inter molecular interactions among the pentacene moieties. In this project our aim was to~~

~~synthesize pentacene thiol 90 which itself could also be a potential candidate for preparing a self-assembled monolayer. Our proposed synthesis of 90 via a deprotection~~

~~reaction of another intermediate pentacene 91 is shown in Scheme 1.12.~~

~~54 Scheme 1.12: Proposed scheme for synthesizing 6,13-pentacenethiol 90 and disulfide linked pentacene oligomer.~~

~~1.2.1.2.1 Synthesis~~

S,S'-6,13-Dihydropentacene-6,13-diyl diethanethioate 92 was prepared from 24 via treatment with Znl2 and thioacetic acid in dry DCM at room temperature following the procedure described in references 92 and 93, except that two equivalents of Zn^ were used instead of one (Scheme 1.13). After aqueous workup, followed by extraction into

~~DCM, both the cis and the trans isomers were recovered, as detected by NMR. The major isomer was isolated by silica column chromatography with a hexane and DCM (1:1)~~

eluent. A cleaned fraction of the major isomer was collected before an impure mixture of the two isomers (for details, see experimental). Since the cis isomer is more polar than the trans isomer, it can be inferred that the major isomer is the trans isomer of 92. The yield of isolated 92 was as high as 90%>. This reaction, also performed using ZnBr2 in a much shorter time span of 5-10 minutes, showed a similar isomeric distribution.

~~Compound 92 is soluble in polar solvents, similar to 89; however, it has much better~~

~~solubility in CHCI3 and DCM but poor solubility in benzene or hexane at room temperature.~~

~~55 HCk^H Znl2 or ZnBr2, HSCOCH3> Chloranil~~

~~DCM, RT, 2h K2C03, 60 °C (90%) Benzene~~

~~Scheme 1.13: Synthetic scheme of pentacene 91.~~

The aromatization of 92 was first performed according to the literature '" using chloranil and K2CO3 in dry benzene under an argon atmosphere. However, an insoluble black solid was recovered after the reaction. In fact the same reaction was also attempted in dry acetone as well as in dry CHCI3 at various temperatures, but a similar insoluble black solid was recovered every time (Table 1.6 (a)). Starting material 92 was recovered when the reaction was done (b) with chloranil but without K2CO3 in CHCI3, or (c) with o-chloranil and K2CO3 in benzene, and (d) with IBX (Table 1.6). Even after varying the reaction conditions by choosing different solvents, different reaction temperatures and different time intervals no improvement was observed. Some other reagents which are

~~also known for dehydrogenation, such as (e) Pd/C146 and (f) DDQ147 were then further~~

~~considered (Table 1.6). In the case of Pd/C, a faint blue coloration was observed after four days; however after the workup, only the clean SM 92 was detected by NMR~~

analysis. In the case of DDQ, the reaction mixture turned green after 24 hours when the reaction was carried out at 100 °C. A strong blue spot separated from starting materials on the TLC plate. The blue fraction was isolated by silica column chromatography using a mixture of DCM and hexane (1:1) in the dark and a blue solid was recovered after drying

~~56 the solvents.~~

~~Obs. Reagents/solvents Reaction Results conditions~~

~~(a) Chloranil, K2C(V 40°-60°C'2d'Ar Black solid dry (benzene or /Dark acetone or CHClj) (b) Chloranil/dry 40°C/17h/Ar SM 92 CHCI3 /dark~~

(c) o-ChloramL K:COy' 60°C/2d/Ar SM92 dry benzene 'dark (d) IBX DMSO 60°C'17h'Ar SM92 /dark (e) Pd-C/dry benzene 80°C/4d/Ar SM92 /dark (f» DDQ/dry toluene 100°Gld/Ar Blue solid, 'dark SM92 Table 1.6: List of observations for the aromatization of 92.

~~The isolated blue solid in CHCI3 had the expected characteristics of pentacene in its UV-Vis spectra with a Xm^x of 621 nm (Figure 1.17) which is very close to that of the~~

~~93 ! pentacene 44 (Xmax = 624 nm). Unfortunately, the H NMR was not clean (Figure 1.17).~~

However, the expected characteristic aromatic multiplets at 8.00 ppm and 7.43 ppm and one singlet at 9.31 ppm were observed. Another singlet at 2.59 ppm integrated for six protons, corresponding to the two CH3 groups of the acetate moiety of pentacene 91.

~~Molecular ion and other fragmentation peaks in the MALDI-TOF mass spectra (using sulfur as a matrix) of the blue solid confirmed the existence of the desired pentacene 91.~~

~~57 1~~

~~5 v/A~~

~~4«3 4"a& '~~

~~CHC1, DCM~~

JL-JA-W^. -in^-i-m * —iitHi. \. If*

~~!!! l,,1-1 11 11 T T T j r T I'"''"'"* •"j ••'•'!'• I J T | ,«•,.....,,:,.. >», ....{. j , ( T " ~i—i—i—)—i—t—!—r~ I ~» r~™" 9 9 1 6 3 pp^~~

~~Figure 1.17: UV spectra of 91 in CHCI3 (top) and H NMR of mixture containing 91 in CDCI3 with expected peaks marked with asterisks.~~

Since the yield of this reaction was very low, another different synthetic route was taken into consideration. Before the aromatization, a deprotection of 91 was performed with K2CO3 in methanol following Han and Balakumar's procedure.148 The general procedure for the reaction is to stir the compounds containing thioacetate (-SCOCH3) groups for half an hour in MeOH in the presence of K2CO3 at RT. A white deprotected thiol compound 93 was obtained only once following this reaction condition (Scheme

1.14). On subsequent attempts, however, 93 was believed to be further converted to the corresponding yellow-green pentacene thio-quinone compound 94 in the reaction mixture. Compound 94 has a slightly shifted *H NMR compared to pentacenequinone 23 58 (see appendix), although the former has no fluorescence and a different Rf with respect to

~~23. It was also observed that white solid 93, could be trapped without any further conversion to 94 when NaBH4 was used along with K2C03 during the reduction (Scheme~~

~~1.14). Thiol 93 was characterized by proton NMR showing two characteristic doublets at~~

~~5.90 ppm and 5.85 ppm corresponding to the methine protons of the two isomers (cis and trans) of 93.~~

~~K2C03, MeOH, 0.5 h~~

~~(i) K2C03, MeOH, 0.5 h, (ii) NaBH4, 20h Scheme 1.14: Synthesis of 93.~~

Further characterization using mass spectrometry and 13C NMR is required for complete characterization of this new compound 93. A further aromatization of 93 with the goal of synthesizing pentacene thiol is planned for future work.

~~1.2.1.3 Pentacene-6,13-Disulfonium Salt~~

In this study, the aim was to synthesize a highly polar pentacene salt which would be soluble in polar solvents and amenable to electrochemical studies.149 Our aim was also to improve upon the stability and crystallinity (with better crystal packing and higher 7i- orbital overlap) of known pentacene derivatives by producing pentacene salts with strong,

59 electron withdrawing substituents. So, in the current project we have proposed to synthesize two pentacenes, 6,13-bis(n-dodecylthio)pentacene 95 and 6,13-bis(ethylthio)- pentacene 96, which could be converted to pentacene-6,13-disulfonium salt 97 (Scheme

~~1.15).~~

~~95 : R = CH2(CH2)9CH3 96 : R = CH3~~

~~Scheme 1.15: Retro synthetic scheme of synthesis of 97 from 95 and 96.~~

The synthetic strategy was inspired by the synthesis of a phenylsulfonium salt described by Srogl and coworkers.150 In a two step process, S-(phenyl) tetramethylenesulfonium PF6- salt was synthesized from thiophenol using triethylamine and 1,4-dibromobutane in ether, followed by treating with NH4PF6 in acetone (Scheme

~~1.16) 151~~

~~SH 1- N(CH2CH3)3 S PF6 0 2- NH4PF6~~

~~Scheme 1.16: Synthesis of phenyl sulfonium salt from thiophenol and 1,4-dibromobutane~~

~~Based on the above synthesis (Scheme 1.16), a retro-synthetic route was proposed to produce 97 from the pentacenes 95 and 96 as illustrated in Scheme 1.17.~~

~~60 Scheme 1.17: Mechanism and retro-synthetic analysis of 97 from 95 and 96.~~

~~1.2.1.3.1 Attempts to Synthesize 6,13-Bis(n-dodecylthio)pentacene~~

~~The synthesis of 6,13-bis(n-dodecylthio)-6,13-dihydropentacene 98, was performed using both Znl2 and ZnBr2 following the procedure described above (Section~~

1.2.1.2.1) and as shown in Scheme 1.18. However, the reaction mixture turned dark brown several times resulting in a low crude yield (63 - 68%). The crude material was highly soluble in any solvent including hexane, and the crude NMR spectrum shows evidence of many impurities. Therefore, a purification of the nonpolar dihydro compound

98 was performed using silica column chromatography with hexane eluent. Two new isomers (cis and trans) were successfully isolated for the first time. Both the isomers were fully characterized using !H and 13C NMR (see appendix). The white crystalline solid trans isomer of 98, was the first fraction from the column and also the major

61 product, similar to the trans isomer of 92 (Section 1.2.1.2.1). It was also noticed that the diastereomers were interchanging when kept at room temperature in the presence of light and moisture. This might be the reason why the isolated yield after separation was even lower (8%> for cis and 34%> for trans isomer) compared to the crude yield.

~~HO-^,H Znl2, HS(CH2)2CH3 DCM,RT, l-2h K2C03, 60 °C S H (crude: 68%) /B-^ ' Benzene 95 S^%~~

~~Scheme 1.18: Synthesis of 98 from 24 and 95 from 98.~~

It was hoped that an aromatization of 98 would easily lead to the formation of 95, as the latter has high structural similarities with the pentacene 43 in Figure 1.6 reported by Kaur and coworkers.93 However, the reaction of the major isomer of 98 with chloranil and K2CO3 in dry benzene under Ar atmosphere, did not produce 95 (Scheme 1.18).

~~There was no trace of 98 after the reaction. This reaction was abandoned without any further attempts at aromatization, in favor of easier routes to synthesize dithioalkyldihydro -pentacenes.~~

~~1.2.1.3.2 Synthesis of 6,13-Bis(»-ethylthio)pentacene~~

~~The precursor of pentacene 96, 6,13-bis(ethylthio)-6,13-dihydropentacene 99,~~

~~92 9, could not be synthesized following the reported procedure using Znl2 in dry DCM. "~~

~~Instead, the reaction was completed within 30 minutes when performed with two equivalent of ZnBr2 and excess thiol, resulting in a single isomer of 99 with a high crude~~

~~62 yield of 95%> (Scheme 1.19). As there was only one isomer present in the crude product~~

~~detected by NMR, there was no need of any further purification. However, it was difficult to remove unreacted ZnBr2 even after thorough washing with water and a saturated~~

~~solution of NaHC03. Hence, a plug column separation was performed with hexane to remove any inorganic byproducts. Off-white colored solid 99 appeared to be much more~~

~~stable compared to 98. However, it rapidly isomerized its other diastereomer in solution phase, even in the dark. The amount of the second isomer was increased from 0%> to 37%>~~

~~within 11 hours (see NMR in appendix). In the solid state, the conversion was much~~

~~slower under light at room temperature. Therefore isolated 99 was stored cold in the dark.~~

~~Scheme 1.19: Synthesis of 99 from 24 and 96 from 99.~~

~~A solution of 99 in dry benzene was first treated with chloranil and K2CO3 and~~

~~heated at 60 °C for three days using a round bottom flask attached to a condenser as~~

~~described in the references.92"9"' After one day, a blue spot was detected by TLC. The spot~~

~~disappeared after the second day leaving unreacted starting materials behind. It turned~~

~~into a heterogeneous black reaction mixture when the reaction was performed for three~~

~~days. In a subsequent trial, the reaction was worked up after one day. Different reaction~~

~~conditions were also tested in order to optimize the reaction conditions (Table 1.7). The~~

~~same reaction, when performed using a Teflon-capped glass bomb, was complete within~~

63 16 hours affording the desired product. The aromatization could also be performed using one drop of Br2 in dry solvents such as CCI4, CDCI3 or CHCI3 for 1-2 hours of stirring monitored by NMR spectroscopy and TLC. In the last procedure however, more than one blue band was observed and the very first blue band contained the product isolated by the

~~.chromatographic separation using hexane.~~

~~Obs. Reagents/solvents Reaction Results conditions~~

~~(a) Chloranil, K2C03/ 60°C/24h/Ar 96, SM99 dry benzene Condenser/dark~~

~~(b) Chloranil, K2C03/ 60°C/16h/Ar 96 dry benzene bomb/dark~~

~~(c) Br2/dry CC14 or RT/lh/Ar 96 CHCl3orCDCl3 /dark Table 1.7: List of reactions utilized to aromatize 99 and synthesize pentacene 96.~~

~~The recovered dark blue solid pentacene 96 in CHCI3 has Amax at 616 nm (Figure~~

~~1.18), which is comparable to the reported Xmax value for bis(decylthio)pentacene (43,~~

/Ymax at 617 nm).93 After chromatographic purification of 96 in hexane, the blue fraction was evaporated and the recovered blue solid was dried either under vacuum or under an argon atmosphere in the dark. However, compound 96 decomposed to a greenish black solid after 24 hours. Thus, the product was not as stable as anticipated and a 13C NMR spectrum of the blue compound could not be obtained. Fortunately, a !H NMR study of the blue compound, before drying, demonstrates all the expected signals. One singlet at

~~9.73 ppm and two multiplets at 8.07 ppm and 7.41 ppm indicate the aromatic protons of~~

~~96. A quartet at 3.07 ppm corresponds to the methylene protons. The corresponding triplet for CH3 (at 1.18 ppm) of the ethyl groups is overlapped with the hexane signals~~

64 (Figure 1.18). Unexpectedly, 96 in solution was stable for four days while being kept in a capped NMR tube in the dark. A molecular ion signal detected by mass spectrometry also confirmed that pentacene 96 was successfully synthesized.

~~Figure 1.18: UV-Vis spectrum (top) and NMR spectra (bottom) of 96 in CDC13 (expected peaks for 96 has been marked with asterisks).~~

Because of its instability, the desired pentacene 96 could not be used to make the proposed pentacene salt 97. Other known reported pentacenes with longer thioalkyl chains (such as butyl, octyl or decyl) ' ~ could, however be used in the future for the same reaction to make a similar pentacene salts.

~~65 1.2.1.4 Attempted Synthesis of 2,3,9.10-TetrakisfbenzvlthioV6q3-~~

~~bis (phenylthio)p entacene~~

It has been established that the substituents at the 6,13-positions of the pentacenes influence their HOMO-LUMO gap to a large extent.93 Moreover, it has been reported that pentacenes with alkylthio and arylthio groups located at the 6,13-positions are more stable than other functionalized pentacenes toward photooxidation.93 Those pentacenes that also have low HOMO-LUMO gaps are potential candidates for use in organic electronics.9" To date however, no attempt has been published to synthesize a hexathiopentacene with thio-groups attached to the 2,3,9,10 (procata positions) and 6,13- positions (center carbons) of the pentacene backbone. In this study, the aim was to understand the electronic effect of sulfur groups at the procata positions of the pentacene.

~~For illustration, the proposed molecular structure of pentacene 100 is shown in Figure~~

~~1.19.~~

~~Figure 1.19: Structure of hexathio-substituted pentacene 100.~~

~~1.2.1.4.1 Synthesis~~

~~Our approach for synthesizing pentacene 100 (Scheme 1.20) was inspired by the work of Polec and coworkers to synthesize 4,5-dithiooctylphthalate from 4,5-~~

66 dichlorophthalic acid.152 Diethyl-4,5-dichlorophthalate 101 was prepared from 4,5- dichlorophthalic acid employing an acid catalyzed esterification in 98%> yield. The chloro groups in 101 were then substituted by thiobenzyl groups when treated with benzylthiol and NaH, to produce diethyl-4,5-dithiobenzylphthalate 102 with a slightly lower yield

~~(72%o) than reported (82%>) for the corresponding molecule when substituted with an octylthio group. " This new molecule 102 was characterized by H and C NMR spectroscopy.~~

~~Cl\^^/COOH Et0H, Toluene Cl^^COOEt Benzyl thiol ^ BnS^^COOEt~~

~~Cl^^COOH H2S04, Reflux ci^^COOEt Slu^^oT BnS^^COOEt (98%) 101 (72%) 102~~

~~Borane BnS^^CH2OH Oxalyl Chloride BnS^^^CHO *~ Triethylamine || T THF,RT RnBnSo-^^ rTCHT nTHr X^K 5d,(99%) tM 2° DMSO, DCM BnS ^^ CHO 103 lh, (93%) 104~~

~~Scheme 1.20: Synthesis of aldehyde 104 from 4,5-dichlorophthalic acid.~~

Compound 102 was further reduced to form l,2-hydroxymethyl-4,5- dithiobenzylbenzene 103 using borane in THF.1:o The white solid 103 was recovered with a high yield (-99%) and characterized by NMR spectroscopy. The diol 103 was oxidized to 4,5-dithiobenzylphthaldehyde 104 by Swern oxidation using oxalyl chloride in dry

~~DCM at -78 °C.154 The crude product was purified by triturating a solution of 104 in~~

~~CHCI3 using hexane and was confirmed by NMR spectroscopy.~~

~~An aldol condensation of aldehyde 104 and 1,4-cyclohexadione in ethanol in the presence of a 10%> NaOH solution yielded 2,3,9,10-tetrakis(benzylthio)-6,13-~~

~~67 pentacenequinone 105 as a yellow solid (following a similar procedure as described in~~

~~Section 1.1.1.5). The pentacenequinone 105 is sparingly soluble in CHCI3 and is much less fluorescent than 6,13-pentacenequinone 23 and was only characterized using H~~

NMR. Due to the insolubility in MeOH, quinone 105 was further reduced using NaBH4 in wet THF following Zeynizadeh's procedure (Scheme 1.21).!42 Both the cis and the trans isomers of 2,3,9,10-tetrakis(benzylthio)-6,13-dihydroxy-6,13-dihydropentacene 106 were detected by NMR spectroscopy.

~~KOH,EtOH YYTTI] NaBH4, 104 " F^F-^F^F^FF^\ jrrp RT Reflux, Id BnS T SBn /",',' BnS (71%) 105 O 17b, (93%)~~

~~H SPh sph BnS > / SBn BnS ZnBr2,DCM V^V^V V^r V Chloranil~~

~~X HSPh QnS ^ ^ XODT "" 'SBn ^\. BnS RT,2h 107 H SPh 60 °C, 2d 1Q0 £ph~~

~~Scheme 1.21: Attempted Synthesis of pentacene 100 from aldehyde 104.~~

The light pink solid containing an isomeric mixture of 106 was used in the next step without any further purification. Diol 106 was treated with thiophenol and ZnBr2 in dry DCM for two hours. The resulting product, 2,3,9,10-tetrakis(benzylthio)-6,13- bis(phenylthio)-6,13-dihydropentacene 107 decomposed during purification using column chromatography. However, the crude NMR spectrum had the expected peaks of the two isomers of 107 as well as some impurity peaks. Aromatization of the crude solid

107 was attempted using chloranil and K2CO3 in CHCI3 for two days at 40 °C in the dark under a N2 atmosphere following the literature.93 The resulting dark greenish-blue 68 reaction mixture was passed through a plug column in hexane and the first dark greenish- blue band was collected. Evidence of pentacene formation was limited to a weak band from 540 - 680 nm in the UV spectrum. The NMR spectrum of the greenish-blue fraction was ambiguous showing only one of the expected aromatic singlets at 9.23 ppm, which matches the reported value for similar thio-substituted pentacenes. However, this evidence is not sufficient to prove the existence of pentacene 100.

~~Compound 106 was also treated once with ^-butylthiophenol instead of thiophenol~~

~~(Scheme 1.22) to improve the solubility of the corresponding dihydro compound 108.~~

Two expected isomers (cis and trans) of 2,3,9,10-tetrakis(benzylthio)-6,13-bis(4'-?- butylphenylthio)-6,13-dihydropentacene 108 were isolated by a column chromatographic separation (see NMR in appendix). However, the resulting compounds did not seem to be stable after column separation. Thus, aromatization to synthesize 2,3,9,10- tetrakis(benzylthio)-6,13-bis(4'-f-butylphenylthio)pentacene 109 could not be performed.

~~Scheme 1.22: Synthetic scheme of pentacene 109 from 106.~~

~~1.2.1.5 Theoretical Study of Thio-substituted Pentacenes~~

~~In an attempt to better understand the electronic properties of known~~

~~69 functionalized pentacenes, as well as assist in directing future synthetic efforts, the~~

HOMO and LUMO energies and respective gap (Egap) of some thio-substituted pentacenes were computed. All model structures were first optimized using the MMFF method and re-optimized using B3LYP/6-31G* (Section 1.1.2.4). The final HOMO,

~~LUMO and Egap values of the pentacenes were obtained from a single point energy calculation using a higher quality triple-zeta basis set (B3LYP/6-311+G**) as suggested~~

~~15: by Grimme and coworkers. " The Egap values computed were compared with the optical band gap (Eg(opt)) values extracted from the corresponding UV spectra, listed in Table 1.8.~~

~~To assess the impact of geometries, the computed values of the HOMO, LUMO~~

~~93 energies and Egap of pentacene 44 were compared with those calculated using B3LYP/6-~~

311+G**//PM3. There is a lower deviation (Egap - Eg(opt)) of the theoretical values (Egap) from the corresponding experimental values (Eg(opt)) of the HOMO-LUMO gaps, for both unsubstituted pentacene (Egap - Eg(0pt) = 0.07 eV) and 44 (Egap - Eg(opt) = 0.19 eV) with geometries optimized using B3LYP/6-31G* level (Table 1.8). Therefore, B3LYP/6-

311+G**// B3LYP/6-31G* was chosen for all subsequent calculations. It should also be noted that Egap for 88 (2.06 eV), 91 (2.06 eV) and 96 (2.08 eV) are in quite good agreement with the values corresponding to their Eg(opt) with less than or equal to 0.13 eV deviation. Following the trend, it can also be predicted that the pentacenes 90 and 100 are promising molecules with lower Egap of 2.03 eV and 2.04 eV respectively. Moreover, all five pentacenes (88, 91, 90, 96 and 100) have a lower band gap than the parent pentacene.

~~70 Compounds HOMO LUMO Esap (eV) (eV) (eV)~~

~~Pentacene -4.94" -2.76" 2.18" 2.11 0.07 b -2.67b -4.96b 2.29b 2.08 0.21~~

~~44 -5.11 -3.06 2.05 I 1-86* 0.19 -5.20b -3.03b 2.17b ! 0.31~~

~~88 -5 36 -3.30 2.06 1.97 0.09~~

~~90 -5.05 -3.02 2.03 _ .~~

~~91 -5 10 -3.04 2.06 1.93 0 13~~

~~96 -5.01 -2 93 2.08 195 0.13 1 100 -5.27 -3.23 2 04 ) _~~

~~1.2.1.6 Conclusions and Future Work~~

Our theoretical studies of the thio-substituted pentacenes (88, 90, 91, 96 and 100) indicate that their calculated HOMO-LUMO gaps are comparable to that of the highly stable thio-substituted pentacene 44, and along with 44 are expected to outperform unsubstituted pentacene in organic electronics applications. Although experimentally we have synthesized pentacenes 88, 91 and 96 on a milligram scale, it is important to prepare these pentacenes on a larger scale in order to carry out better characterization and further probe their device properties. The difficulties associated with the synthesis of pentacenes

~~90 and 100, on the other hand, call for a deeper understanding of the aromatization of their corresponding dihydro precursors.~~

~~71 1.2.2 Synthesis of Sulfur and Chloro Substituted Anthracene~~

Despite the expectation of increased stability of acenes with thioalkyl or thioaryl substituents, we faced certain difficulties with the dehydrogenation and the aromatization of dihydropentacenes containing sulfur-functionalities. Hence, we started to search for other paths for incorporating thio groups through C-S bond formation. The study of

~~Takeuchi and coworkers for arylthiolation of aromatic compounds using disulfide radical cations generated by oxidation of diaryl disulfides156 proved to be of great interest to us~~

(Scheme 1.23). This thiolation preferentially generates para-substituted diaryl sulfide products. Several acids such as H2SO4, TFA, FSO4H, SbCls, etc. have been used to catalyze the radical reaction. The use of SbCls in DCM was the most promising set of conditions.

~~SbCl PhS-SPh + Ar-H 5 Ar-SPh + PhS-H DCM, RT Scheme 1.23: Arylthiolation of aromatic compounds using disulfide.156~~

~~1.2.2.1 Synthesis of 9,10-Bis(phenylthio)anthracene~~

~~Since there was no precedent for any acenes undergoing such a transformation, anthracene was used as a model compound to synthesize 9,10-bis(phenylthio)anthracene~~

110.1:>7 According to the literature, the duration of the reaction was 30 minutes.156 In our laboratory, there was no evidence for anthracene starting materials after ~5 minutes of reaction time at which time there were already several different products observed by

~~TLC. We therefore opted to stop our reactions after 10 minutes. We were able to~~

~~72 synthesize 110, along with some other interesting byproducts, in significant yields~~

(Scheme 1.24 and Table 1.9) and characterized these products by NMR spectroscopy and mass spectrometry (see appendix). Along with 110, the other byproducts were isolated using preparative TLC plates. These byproducts included 9-(phenylthio)-anthracene 111,

~~9-chloro-10-(phenylthio)anthracene 112, 9-chloroanthracene 113 and 9,10- dichloroanthracene 114 (Table 1.9). To increase the yield of either anthracene 110 or~~

9,10-dichloroanthracene 114, we modified our reaction conditions by changing the molar concentrations of diphenyl disulfide and SbCls with respect to anthracene leading to five different observations, as shown in Table 1.9. It was possible to increase the percent yield of 110 by 21.6%) by increasing the concentration of diphenyl disulfide by ten-fold (obs.

~~4). Also, when omitting diphenyl disulfide, the yield of 114 was enhanced to 41%o (obs.5 in Table 1.9).~~

~~Scheme 1.24: Synthesis of diphenylthioanthracene 110.~~

73 a obs. \ B C SX) .JO COO —> a r coo ^FF^FF ci o a 110 in 112 113 114 1 1 1 1 —> 7.62% 20.9% 36.16% 31.07% 4.23 2 1 2.5 1 - -> 7.32% 51.24% 13.7% 27.67% - 3 1 2.5 2 —> - - 77.51% - 22.48% 4 1 10 1 - > 29.18% 14.21% 45.93% 7.86% 2.79% 5 1 0 3 —> - - - 58.99% 41% Table 1.9: Percent yields of different products isolated from the reaction of a Scheme 1.24, calculated from their respective NMR spectra.

~~We were hoping for an analogous result with a pentacene system such that we could avoid the problematic aromatization discussed previously (Section 1.2.1).~~

~~Therefore, bare pentacene as well as several other functionalized pentacenes containing phenyl groups and phenylethylthio groups at the 6,13-positions (synthesized by Dr.~~

Irvinder Kaur) were subjected to the same reaction conditions (Scheme 1.25). However, mostly quinone 23 was recovered from each of these reactions without any thio- pentacene compounds. These results indicate that such reaction conditions are probably too harsh for pentacenes and could not be used for the functionalization of pentacenes or any larger acenes.

~~R O~~

~~R R = H,Ph,-SCH2CH2Ph~~

~~Scheme 1.25: Reaction of pentacenes with SbCl5 and diphenyl disulfide.~~

~~74 1.2.2.2 Application to [601Fullerene and Carbon Nanotubes~~

~~As we observed, SbCls turns out to be a moderately harsh reagent for pentacenes, and it seemed interesting to study the effect of the above reaction conditions on~~

[60]fullerene and CNTs. The reactions of [60]fullerene and MWNTs with SbCl5, with or without diphenyl disulfide, are shown in Scheme 1.26. Usually when reacted with pentacenes or amines, [60]fullerene changes color from purple to brown in solution. A brown color was also observed when the reaction was performed with [60]fullerene in

~~CS2 instead of DCM (Scheme 1.26). The NMR from both reactions involving~~

~~[60]fullerene has no proton signals in the aromatic region. However, evidence for addition of chlorine was detected in a mass spectral analysis. Extensive chlorination of~~

[60]fullerene (up to n = 21) was achieved without the addition of diphenyl disulfide. In contrast, mono-chlorination of C60 was detected when diphenyl disulfide was added in the reaction mixture (see appendix). This seems reasonable because the relative concentration of SbCl5 decreases with the addition of diphenyl disulfide. On the other hand, when MWNTs were sonicated with SbCls and diphenyl disulfide (Scheme 1.26) in

~~CS2 for seven hours, the resulting MWNTs had slightly better solubility in MeOH and worse in CHCI3 as compared to pristine MWNTs.~~

~~75 CSo (a)C60 +( Vss /=\ + SbCl5 -*- C^nC'60v l X=/ ~\) 5-10min,25°C S-<\ /> 5-1 MS: 756.05~~

~~CS2 C (b)C60 +SbCls 6oCln 5 5-10min,25°C MS: 1394.15 (n=19) MS: 1465.05 (n=21)~~

~~rA c „ _ CS2 (c)MWNT+f Vsx /=\+SbCl5 f-MWNT S—(\ /) Sonication 7h, 60°C~~

~~Scheme 1.26: Reaction of SbCl5 with (a) C6o and diphenyl disulfide, (b) Ceoonly, and (c) MWNT and diphenyl disulfide.~~

~~1.2.2.3 Future Direction and Conclusions~~

This method for formation of C-S and C-Cl bonds using SbCls is novel and useful for functionalization of smaller acenes such as anthracene. However, it is evident that pentacenes are decomposed using these conditions. SbCl5 seems to be reactive with

C6o resulting in insoluble chlorinated Ceo adducts. However, it would also be important to attempt such reactions with SWNTs to functionalize them. Raman spectrometry and TEM need to be utilized in order to more fully characterize these CNTs.

~~1.2.3 Towards the Synthesis of Larger Acenes; Sulfur-Stabilized Nonacene~~

~~The prediction that larger acenes will have smaller HOMO-LUMO gaps (Section~~

~~1.1.2.4) makes them highly desirable for organic electronic applications. The scarcity of large acenes, on the other hand, indicates challenges associated with their synthesis. This~~

76 is because the stability and solubility of acenes decrease with their chain length. In this study we propose to synthesize sulfur-stabilized nonacenes. This was inspired by the fact that sulfur increases the photooxidative resistance of smaller acene molecules. The proposed nonacene molecule was designed with several ^-butyl groups to improve the solubility and promote ease of handling and characterization in the solution phase. The retrosynthetic analysis of 1,4,6,8,10,12,15,17,19,21-deca(4'-^-butylphenylthio)nonacene

~~115 from 1,4,8,12,15,19-hexa(4W-butylphenylthio)-6,10,17,21 -tetrahydroxy-6,10,17,21- tetrahydrononacene 116 is shown in Scheme 1.27.~~

~~115 116~~

~~Scheme 1.27: Retrosynthetic analysis of 115 from 116.~~

Compound 116 is a reduction product of hexa(4'-?-butylphenylthio) substituted nonacenediquinone 117 which in turn could be synthesized from 6,9-bis(4'-£- butylphenylthio)-l,4-anthracenequinone 118 and a bis-o-quinodimethane precursor 119

~~(Scheme 1.28 (a)). The strategy of this key step was inspired by the synthesis of~~

~~6,10,17,21-nonacene diquinone from 1,4-anthracene quinone and octabromodurene in our laboratory158 (Scheme 1.28 (b)).~~

~~77 O Br Br O O Nonacened iquinone Scheme 1.28: (a) Synthetic approach of 117 from 118 and 119 and (b) reported synthesis of nonacenediquinone.~~

~~1.2.3.1 Attempt to Synthesize l,4,8,12,15.19-Hexa(4,-f-butvlphenylthio)nonacene~~

We were successful in the synthesis of brick-red colored anthracenequinone 118 from the reaction of l,4-bis(4'-?-butylphenylthio)-2,3-bromomethylbenzene 120 and benzoquinone using KI in a Teflon-plugged glass bomb at 110 °C for 17 hours, following the procedure of Swartz and coworkers159 (Scheme 1.29). The o-quinodimethane precursor 119 was prepared by the treatment of l,4-bis(4'-?-butylphenylthio)-2,3,5,6- tetramethylbenzene 121 with NBS and AIBN. However, dibromo-compound 120 could not be synthesized using NBS in CHCI3 or in CCI4. Instead, 120 could only be prepared from l,4-bis(4'-?-butylphenylthio)-2,3-dimethylbenzene 122 when Br2 was used in CC14 with irradiation of light from a 250 Watt lamp (Scheme 1.29). Both 121 and 122 were prepared in good yield by refluxing the corresponding aryldibromo compounds 123 and

~~124 in the presence of para-f-butylthiophenol with CS2CO3 and Cul, in DMF for two days~~

~~(Scheme 1.29). 16°~~

78 NH9 O O NHCOCH, NHCOCH, NH, Br 2 (i)NaN02,HBr T* • A x, NBS, CHCU (a) 0 HCl.EtOH -5-0 °C » (j *V RT, 3min, Reflux, 20h, Reflux, Id (ii) HBr, CuBr ^F^ (79%) (98%) Reflux, (76%) J, 127 (89%) Br Br Br 126 125 124

~~Cul, Cs2C03 (isolated: 77%) Br KI,DMF, 17h Reflux, 2d, bomb, 110 °C, (isolated: 88%) (isolated :61%) 122 120~~

~~Br2,12 NBS,CHC13 Br. (b) SH Br XC DCM, Reflux, Cul, Cs C0 AIBN, Reflux Br Br 1.5h, 85% 2 3 Light, 3h, (97%) Br Reflux, 2d, 119 123 ( 90%) 121 Scheme 1.29: Syntheses of 118 and 119.~~

Compounds 123161 and 124162 are known and their syntheses are reported in the literature. White crystals of dibromo-precursor 123 were prepared in 85%> yield by refluxing durene in DCM in the presence of molecular bromine and a catalytic amount of iodine. Dibromo-compound 124 was prepared by employing the Sandmeyer reaction by refluxing a mixture of l-amino-4-bromo-2,3-dimethylbenzene 125 and NaN02 (prepared at -5-0°C) and CuBr for three hours. After extracting the organic layer with DCM, 124 was purified via silica column chromatography with hexane eluent resulting in a white crystalline solid. Compound 125 was prepared after deprotection of N-(4-bromo-2,3- dimethylphenyl)acetamide 126 by an acid hydrolysis. To avoid any side reaction of the

~~79 amino group, the para-bromination of 126 was carried out using NBS after protecting the amino group of l-amino-2,3-dimethylbenzene to form N-(2,3-dimethylphenyl)acetamide~~

~~127 using acetic anhydride16^ (Scheme 1.29). All compounds were characterized by~~

~~NMR spectroscopy.~~

~~It should be mentioned that during the synthesis of 118, a small amount of a very bright orange-red fluorescent pentacenequinone 128 was always produced. The quinone~~

128 is also a new molecule and an important precursor for 1,4,8,11-thioaryl substituted pentacene. Compound 128 can also be synthesized when two equivalents of 120 are reacted with one equivalent of benzoquinone or, when one equivalent of 118 is reacted with one equivalent of 120 using KI in DMF in a Teflon-capped glass bomb at 110 °C

~~(Scheme 1.30).~~

~~172 0=0=0 1 eq. 120 2 eq' 12° KLDMF, 17h V^V^V KI, DMF, 17h bomb, 110 °C, S^^ O S bomb, 110 °C, 128 Scheme 1.30: Synthesis of 128.~~

~~The newly synthesized compounds 118 and 119 were then reacted with KI in~~

~~DMF at 100 °C in a Teflon-capped glass bomb for 13 hours to form nonacenediquinone~~

~~117 (Scheme 1.31). The diquinone 117 is a bright red solid that is soluble in CHC13~~

~~(>DCM>ODCB) and was characterized by H NMR spectroscopy. However, even after a large number of scans, a 13C NMR spectrum could not be obtained. Nonetheless, a~~

~~80 molecular ion peak in the mass spectrum confirmed the existence of the quinone.~~

~~Scheme 1.31: Synthesis of 117.~~

Both 117 and 118 were also characterized by cyclic voltammetry and UV-Vis spectroscopy (Figure 1.20). Interestingly, both the electro-chemical (Eg(cv)) and optical band gaps (Eg(opt)) of 118 are lower than that expected for any anthracenequinone. Also, diquinone 117 had a higher difference between its measured values for Eg(cv) (1.9 eV) and Eg(opt) (2.3 eV) than that for 118 with Eg(cv) = 2.0 eV and Eg(opt) = 2.19 eV This inconsistency might be due to oxidation of sulfur on 117 by electrochemical methods.

However, the A^ax (482 nm, and a shoulder at 699 nm in CHC13) value for 117 is red shifted compared to the A.max (465 nm in CHCI3) value of 118 (Figure 1.20), which makes perfect sense since 117 contains an anthracene moiety while 118 has a naphthalene moiety.

~~81 if~~

~~i '< i \ i i i t 1 = 676 nm ' I = \nax 465mil V \ ^Am„ = 482nm~~

~~« avelesgifa (run) 1\ avelength (am) Molecule: 118 Molecule: 117~~

~~. E13 =1414 5 4 s"0- n E'-0x=1387 5 /( 1 * (.•*-~~

~~fl ; A - 826mv// s 5J- 1306mV /7 A ——•' X •632mV //"" "~ -650mV 5>> 3-1-~~

~~E12 d=-720 5 |l469mV ,, _ Rt f fc Red--'-'8~~

~~1 U S "2€ 0 -o 1C o a Profit 3i{mY)~~

~~Figure 1.20: UV-Vis and CV of 118 (left) and 117 (right).~~

~~Since the yield of 117 was very low, the next step was also carried out on a very~~

~~small scale. The reduction of 117 was achieved after treatment with NaBH4 by the wet-~~

~~THF method142 to synthesize a lemon yellow fluorescent nonacenetetrol 116 (Scheme~~

~~1.32). It could only be characterized by a mass spectrometnc analysis with a molecular~~

~~ion peak at m/z =1531 and by a UV-Vis spectrum with a peak at 422 nm in CHC13~~

~~(Figure 1.21).~~

~~82 S HO^H ? HO„H S NaBH4, RT rYY r*^ r^TY W^ 117 ^ -^V^^N^^^^r THF, 2h, ^v^^><^^ X H OH ^ ^H OH J ^ 90% XXf.~~

~~Scheme 1.32: Equation of synthesis of 116 from 117.~~

~~15312 11 U HO H S 15142 HO^H HOH~~

~~Molecular Weight: 1532.21~~

~~"*\Xm„ = 422nm~~

~~Wavelength (nm)~~

~~14876~~

~~13S10 13668 13B75 I13B8 J1S3461 147B4 F\^. A A /\ A , I ' ( MffliailBBtlllllSMlfflMffl)~~

~~Figure 1.21: Mass spectrum and UV-Vis spectrum (inset) of 116.~~

~~At this stage, the synthesis of 1,4,8,12,15,19-hexa(4'-^-butylphenylthio)nonacene,~~

~~129 was attempted by aromatizing 116 using SnCLVHCl.41 The reaction of 116 (Scheme~~

1.33) was monitored by TLC and UV fluorescence. The reaction was complete almost immediately after the addition of concentrated H2SO4 to the reaction mixture. The fluorescent color of the reaction mixture changed from lemon yellow to orange. Although

83 the molecular ion peak of 129 (m/z = 1464) was detected by MALDI-TOF mass spectrometry (Figure 1.22) using molecular sulfur as a matrix, there was no significant absorbance at longer wavelength in its UV-Vis spectrum which is contrary to what is expected for large acenes. The NMR spectrum of the resulting compound was inconsistent with either SM or the desired product 129. Additionally, when 117 was refluxed with HI in acetic acid for five days164 the diquinone 117 was recovered without any change. At this stage we have undertaken theoretical studies to better understand the electronic properties of the desired functionalized nonacene.

~~SnCl2, HC1 H2S04 u^nir I Dioxane, H U±1 Sy^ dark, AT~~

~~Scheme 1.33: Synthesis of 129 from 116.~~

~~Isjrt 395 IHV[«m= 188245 a : PfoBs W73 Smoosti Av 20 -Basetne 80 287 4~~

~~70 289.5~~

~~60 •» Molecular Weight: 14 64.1 i~~

~~30: 28 !4 20- i 231.$ 14633 10J~~

~~...... >.„„_,Aj_vy^^^^'j^4/y.yklf-V^Wl.>. 300 400 500 800 SB 1000 1100 1200 1300 1403 1500 1600 __ Mass'Ctsatoa __™_„ Figure 1.22: Mass spectrum of 129.~~

~~84 1.2.3.2 Theoretical Studies of Arylthio Substituted Nonacenes~~

According to Bendikov and coworkers, acenes larger than hexacene have an open-shell singlet ground state electronic configuration associated with a total spin character () greater than zero.136 This prediction was made based on calculations for larger acenes using unrestricted DFT methods (e.g., UB3LYP/6-31G(d), Section 1.1.2.4).

~~We corroborated this prediction at a higher level of theory (i.e., UB3LYP/6-~~

311+G**//B3LYP/6-31G*) to understand the electronic properties and stability of nonacene 129 and nonacene 115. For the sake of computing time, the ^-butyl groups were omitted such that (hexaphenylthio)nonacene 130 and (decaphenylthio)nonacene 131 were used as models for the calculation. The calculated HOMO and LUMO energies,

2 respective gaps (Egap in eV) and values of nonacenes 130, 131, unsubstituted nonacene and thio-substituted nonacene 132m are listed in Table 1.10. It has been found that the HOMO-LUMO energies and Egap of 130 and 131 are lower than that of the parent nonacene. However, both molecules 130 and 131 have potential radical character associated with their ground state electronic configurations. Nonacene 130 has a ground state configuration with radical character and a total spin equal to 1.04a and 1.29b before and after annihilation of the first spin contaminant, respectively (Table 1.10).

~~Despite additional sulfur substituents, the of 131 is greater than that of 130, which is in turn greater than that of unsubstituted nonacene. It has been reported that a stepwise~~

•y i radical addition of either triplet oxygen ( O2) or singlet oxygen ( O2) becomes more energetically favorable with increasing total spin of the acene."8'125 In that respect, nonacenes 130 and 131 should be highly reactive due to high ~~values. Thus, the~~

85 calculations imply that syntheses of corresponding nonacenes 129 and 115 would be difficult. These results also predict that stabilities of nonacenes are not directly proportional to the number of sulfur functional groups. Additionally, sulfur functional group position may dramatically impact the total spin character () of larger acenes.llb This is exemplified in the case of (decaphenylthio)nonacene 132, in which four additional -SPh groups are attached at the procata (2,3,13,14) positions of 130 (Table

~~1.10). 118~~

~~Compounds HOMO LUMO (eV) (eV) (eV)~~

~~-4 69 , -3.08 1.61 1.20~~

~~130 SPh SPh SPh -4 84 -3 25 1 59 104b SPh SPh SPh 129* 131 SPh SPh SPh SPh SPh b -4 98 -3 38 1 6 1 10 SPh SPh SPh SPh SPh 161" 132 -4 7 -3.7 I 0~~

~~2 118 Table 1.10: The energies of HOMO, LUMO, Egap, (in eV) and ~~of nonacene , 130, 131 and 132118 calculated using the B3LYP/6-311+G**// B3LYP/6-31G* method are listed.~~~~

~~1.2.3.3 Conclusions and Future Direction~~

~~We proposed to synthesize (hexaphenylthio)nonacene 129 and~~

~~(decaphenylthio)nonacene 115. To that end, we synthesized two new compounds, namely anthracene quinone 118 and nonacenediquinone 117, both of which were characterized by~~

~~:H and 13C NMR spectroscopy, mass spectrometry, UV-Vis spectroscopy and cyclic~~

~~86 voltammetry. However, aromatization of the corresponding tetra-hydroxy compound 116 proved difficult. Our theoretical calculations predict that both targeted nonacenes (129~~

~~and 115) with sulfur functional groups possess greater spin or radical character and are therefore less stable than the unsubstituted nonacene.~~

~~1.2.4 Spectroscopic Studies of Acene Quinones and Hydroxyacenes in Concentrated~~

~~Sulfuric Acid~~

~~Clar first observed that when 6,13-pentacenequinone 23 was treated with~~

~~concentrated H2SO4 acid (cone. H2SO4), it immediately turned into a deep blue solution with strong red fluorescence1 similar to that of pentacene.165 Moreover, the UV-Vis~~

~~spectrum of the deep blue solution of 23 exhibited pentacene-like characteristics with~~

Xmax 628 nm (Figure 1.23). This value is bathochromically shifted compared to the A^*

~~of pentacene (577 nm) in DCM. Similarly, Clar reported a detailed UV-Vis spectral study~~

~~of various acene molecules in organic solvents.1 He also reported the changes of~~

~~coloration due to the acid-treatment of acene quinones.l However, detailed studies of the~~

~~UV-Vis spectroscopic analysis for acid treated acenes or acene quinones have not been reported. We attempted to verify whether the aforementioned observation of 23 in cone.~~

~~H2SO4, is similar for other acene derivatives. Since there are very few available acenes~~

~~larger than the pentacenes, creating a library with the UV-Vis characteristics for all the~~

~~available acene derivatives in cone. H2SO4 seemed prudent. Analysis of these UV-Vis~~

~~characteristics made it possible to predict similar characteristics of functionalized larger~~

~~acenes through extrapolation. 87 20-. 2 5- 1 8-~~

~~I ' I ' I ' I 350 400 &00 §00 ?&& 300 40& 500 600 700 800 Wavelength (nm) Wavelength (nm)~~

~~Figure 1.23: UV-Vis spectra of pentacene in DCM (left) and 23 in cone. H2S04 (right).~~

~~1.2.4.1 UV-Vis-NIR Study of Acene Derivatives in Concentrated Sulfuric Acid~~

~~The UV spectra of different acene quinones and hydroxyacene derivatives in~~

~~cone. H2SO4 were studied. All of these acene quinones and hydroxyacene derivatives in~~

cone. H2SO4 have an associated characteristic /?-band in their UV spectra (longest wavelength). The structures of the acene derivatives (23, 116, and 133 - 146) whose properties in cone. H2SO4 were studied are listed in Figure 1.24. It should be mentioned that all the quinones have already been synthesized by Miller's group and the hydroxy

~~compounds were synthesized using the wet THF method142 and characterized by mass~~

~~spectrometry. The corresponding >^ax values of these compounds in cone. H2SO4 are listed in Table 1.11 along with their observed color and fluorescence color in cone.~~

~~H2SO4 solution.~~

~~88 O 133 O 134 O 135~~

~~OH OH~~

~~OH 137 OH 138~~

~~Figure 1.24: The structures of acene quinones and hydroxyacenes whose properties in cone. H2SO4 are studied.~~

89 Molecules Acene Derivatives •""mar" * ?w(3> Color (nm) . (nm) (nm) solution/fluorescence 133 Anthracene quinone 409 - - Yellow/orange 23 Pentacene quinone 628 578 _ Blue/red 134 Heptacene quinone 808 729 _ Forest green/- 135 Nonacene quinone 1071 1011 _ Goldenyellow/- 136 Anthracene diol 400 353 _ Yellow/- 24 Pentacene diol 761 711 _ Green/red 137 Heptacene diol 943 833 _ Parrot green/- 138 Nonacene dioi 1159 1074 940 Brown/yellow 139 Pentacene diquinone 385 _ _ Yellow/- 140 Nonacene diquinone 698 634 _ Greenishblue/- 141 Pentacene tetrol 766 705 - green/parrot green 142 Nonacene tetrol 1073 942 776 Golden yellow green/- 143 Heptacene diquinone 707 _ _ Forest green/- 144 Nonacene diquinone 792 - _ Pale yellow/- 145 Heptacene tetrol 932 836 _ Green/mild yellow 146 Nonacene tetrol 1390 1179 _ green/marune 116 Nonacene tetrol 1220 . . Greenish /mild yellow Table 1.11: List of acene derivatives treated with cone. H2SO4 and measured Xmax values with solution color at RT and fluorescence color under UV light.

~~We observed a shift of the Xmax values at longest wavelength for acene quinones and acene diols in cone. H2SO4 with an increase in the number of benzenoid rings (ri).~~

~~This bathochromic shift in the A^x-values is illustrated in the plot of their UV-Vis-NIR spectra (Figure 1.25).~~

90 p hrj o ^. Sn3 TO CD *•=« a. ffi o l—i rr> ls» Normalized Absorbance (71 Normalized Absorbance S3 n H O O -* -» N> hO OJ O •fe. S3* O Ol O Ol O Ol o o S3 CD I I I I o o 1,1.1 .1 a o en 3 ho O B" o- O -i^ Cun o SP ^ ^ QpnD a a :D % n •• • sr L / D o »-t o - fen-ft n ^ °.,° B o CD V O FF & o f\^^O O°v ^0 >, I> ^ v> "CaD CO o -— o • r-tft-- oCT>- H jP *J o § o D n • D 3i O s > c a /ar k->• 0) Iv ^o 3 *C3 < o m < 2. cx> I C i-i n 00 CD O X "0 > CD CD" C z I T] 3 0 CD £> •-t o- 3 O o 3 r/i UJ 3 o T3 3 i"H" If ^> 5. O 0 CD CO 3

CO * 3 T3 tac e 3 tac e CD 1 ^*S>, "V* ace i TS CO CO CO 3* O ZT :n zr >-h O o o o —, o 0 CO X 3 0 CD CD L- t^ ^ °. 3 3 o CL 3 o -J o ^t 0 0 0 0 ** 5 0 CD .Q !-n S: Q. a ^ C n 0 o 1 Htj 3 ° c M _j- E 3' J2 2. o o O 3' o C O O o o w l_j /****\ ^—v 3 3 3" 1 tf^ C »-* IN* 3 w 0 CD P 1 F QO *• 0 o O CD Js.. i If •w^ 3 - O i If • O 0 § & O m o IK >—' II g _J, O) if cn 3' o~ o' o o o CD l/i J» S3 a. More interestingly, we also found a trend in the bathochormic shifts of A™ax with a

~~linear correlation between ^max and n for acene quinones and acene diols in cone. H2SO4~~

~~for n = 3, 5, 7, 9 (Figure 1.26). This is similar to what is observed with acene molecules~~

~~(for n = 3 - 7) in organic solvent medium.~~

~~Acene monoquinones (133, n=3) (23, n=5) (134, n=7) (135, ni=9)~~

~~Acenediols~~

~~(136. n=3) E (24,n=5) c U37,n=7) J (138. n=9)~~

Acenes Acenediols -* Linear Fit R2 =0.9757 (Anthracene, n=3) Acenequinones • Linear Fit R2 =0.9948 (Tetracene, n=4) Acenes • Linear Fit R2 =0.9988 (Pentacene, n=5) (Hexacene, n=6") 3 4 5 6 7 8 9 (Heptacene, n=7) n (number of linearly fused benzenoid rings)

Figure 1.26: Plots of Xmax-values at longest wavelength of solution of acene monoquinones (red circle), acenediols (blue triangle) in cone. H2SO4 and reported Amax of acenes (black square) (Xmax -values of acenes in DCM are taken from ref-13 for n=3,4,6, and from ref-113 for n=7 and n=5).

~~UV spectra for acene diquinones and tetrahydroxy acenes either with or without~~

~~functional groups in cone. H2SO4 did not demonstrate a similar correlation (Figure 1.27).~~

~~This is likely due to the influence of variable charge delocalization. That is, the degree of red shifting of the A.max values is influenced by the nature and the position of substituents~~

~~on the acene backbones. However, irrespective of any functionalization, all the~~

92 hydroxyacenes have red shifted Amax values for the /j-band (at longest wavelength) as compared to the corresponding acene quinones. This is due to the formation of greater charge density of hydroxyacenes after dehydration as compared to that of the corresponding acene quinones after protonation using cone. H2SO4 (c.f. Section 1.2.4.2 and Figure 1.29)

~~1400- • 146~~

~~1300- Acenetetrols • Linear Fit R =0.7740 Acene diqui no>ne s 2 ^ (139,n=5) 1200- Acene diquinones • Linear Fit R = 0.8009 -*' 116 fl43, n=7) 1100- (140,11=9) • 142 (144, n=9) 1000-~~

~~Acenetetrols jj 900- (141, n=5) 1 800 (145, n=7) 700-1 (142, n=9) (116, n=9) 600 (146, n=9) 500~~

~~Ann~~

~~1 1 1 1 1 1 1 1 1 1 1 5 6 7 8 9 n (number of linearly fused benzenoid rings)~~

~~Figure 1.27 Plots of A^x-values at longest wavelength of solution of acene diquinones (red circle), acenetetrols (black square) in cone. H2SO4.~~

To probe the mechanism of acene acid treatment, we have studied the stability of acene derivatives in cone. H2SO4. For example, the blue solution of 23 in cone. H2SO4 in a capped vessel is highly stable even in the presence of light. Hence, it can be concluded that there is no photo-degradation occurring. But in open air atmosphere (cap-off), the

93 Amax decreases with time. However, photooxidation of the solution seems to be unlikely since cone. H2SO4 is a highly oxidizing agent. Furthermore, when the cone. H2SO4 solution was diluted with water, yellow solid 23 without any remaining acene characteristics was formed. Thus, it could be inferred that the uncapped solution of 23 in cone. H2SO4 actually reacted with ambient moisture and not with oxygen. The plots in

~~Figure 1.28 illustrate the decrease of Amax with respect to drop-wise addition of water.~~

~~200 250 300 350 400 450 500 560 800 650 700 Wa\ elength (nm) Figure 1.28: Decrease of Amax of 23 in cone. H2SO4 with respect to gradual addition of 52 drops of H2O in presence of light and air.~~

~~1.2.4.2 Proposed Mechanism~~

~~The acene characteristics detected in the UV spectra for acene derivatives in cone.~~

H2SO4 could be due to the cationic charges produced in acene derivatives via treatment of the acid are free to delocalize throughout the acene backbone and therefore behave 94 similar to an acene in solution. Our proposed mechanism regarding the chemistry of 23 and 24 reacting with cone. H2SO4 is shown in Figure 1.29. It was assumed that in the

~~2+ case of 23, the cationic charges of intermediate [23-H2] would be delocalized between~~

2+ the aromatic carbons and the oxygens. However, intermediate [24-H2] can dehydrate twice to produce pentacene carbodication ([pentacene]2+). Due to a reduced electron withdrawing effect for dehydration, all the hydroxyacenes in cone. H2SO4, have red shifted Amax values for the p-bmd (at longest wavelength) with respect to the

~~2+ corresponding acene quinones. The proposed mechanism of quenching [23-H2] in cone.~~

~~H2SO4 by the treatment of water to produce compound 23 is also described in Figure~~

~~1.29.~~

~~Figure 1.29: The proposed mechanism of (a) acid treatment of 23, (b) 24, and (c) the mechanism of water neutralizing the cationic state of 23 in cone. H2SO4 medium.~~

95 To support the proposed mechanism, we have performed NMR experiments of 23 and 24 in concentrated D2SO4 (see appendix). We were able to get clean *H and 13C NMR spectra of 23 in concentrated D2SO4. The lH NMR spectrum of 24 (in concentrated

~~D2SO4) shows a single broad peak which is likely due to the alcohol proton of 24.~~

Unfortunately, no cationic carbon peak was detected for 23 and 24. Hence, to understand the detailed mechanism of acid-treated acene derivatives and trap the cationic state of 23, further NMR and UV analysis in super acid medium is necessary.

~~1.2.4.3 Conclusions and Future Direction~~

We demonstrated that acene quinones and hydroxyacenes in cone. H2SO4 medium show acene characteristics as evidenced by UV-Vis-NIR spectroscopy. We observed a trend of increasing Amax values for the /j-band (at longest wavelength) with increasing length of the acene derivatives. This can be correlated to acene behavior in organic solvents (Figure 1.26). The Amax-values of hydroxyacenes in the sulfuric acid are red- shifted compared to the respective acene quinone values. The red shifts are likely related to greater cationic character in the species generated from hydroxyacenes (Figure 1.29).

~~However, for further verification, acene cations should be studied by NMR spectroscopy.~~

~~96 CHAPTER 2~~

~~2. SYNTHESIS AND STUDY OF CYCLACENES AND CYCLACENE DERIVATIVES~~

~~2.1 INTRODUCTION~~

~~Cyclacenes are a class of cyclic 'hoop-' or 'belt-' shaped conjugated molecules consisting of linearly fused benzenoid rings that were first envisioned in 1954 by Edgar~~

Heilbronner.166 While still synthetically unavailable, cyclacenes can be found as substructures of fullerenes and zigzag carbon nanotubes. Examples of such occurrence in fullerenes are found in the equatorial belt of [78]fullerene with nine benzenoid rings forming a [9]cyclacene moiety (Figure 2.1 (a)) and in the equatorial belt of [84]fullerene with ten benzenoid rings forming a [10]cyclacene moiety (Figure 2.1 (b)).167'168 A

~~[10]cyclacene, 147 is also shown in Figure 2.1.~~

~~147 a b~~

~~Figure 2.1: [lOjCyclacene 147; equatorial belts of (a) C7g representing [9]cyclacene and (b) Cg4 representing [10]cyclacene moiety (n -bonds omitted for clarity).~~

97 Zigzag carbon nanotubes (CNTs) can be described as polycyclacenes where each cyclacene monomer is bound such that n-conjugation is further extended down the long axis of the nanotube.169 An open-ended (10,0) zigzag SWNT (a) containing repeating moieties of [10]cyclacene (147) is shown in Figure 2.2.

~~Figure 2.2: (a) Open-ended (10,0) Zigzag SWNT and [10]cyclacene (147).~~

~~Cyclacenes with 'n' annellated six-membered rings are generally called~~

~~"[n]cyclacene".10 However, an alternate naming scheme for cyclacenes, introduced by~~

Gleiter and coworkers, allows for description of carbocyclic belts containing non- benzenoid rings. Such compounds are described as "[m]„cyclacenes", where 'm' stands for the number of sides of a single ring moiety (e.g. m = 6 for a benzenoid ring) and V again stands for the number of annellated 'm'-membered rings.1 ' Hence, according to their method, 147 would be named as [6]incyclacene. This nomenclature is useful for describing a system such as [6.8]3cyclacenesm composed of both six- and eight- membered rings (Figure 2.3), where the three in the subscript represents the number of repeating units. In this text, however, only benzenoid cyclacenes will be discussed and as a result, the simple [ri] cyclacene nomenclature will be used.

~~98 Figure 2.3: [6.8]3cyclacene.~~

~~2.1.1 Theoretical Studies of Cyclacenes~~

Since the discovery of the carbon allotropes buckminsterfullerene (C6o)S?2 in 1985 and carbon nanotubes in 1991,1 3 it has been theorized that aromatic compounds are not limited to planar structures, but can bend while retaining some aromatic stability.174

Despite several attempts to synthesize such belt-shaped molecules, there is no evidence for formation of parent or functionalized cyclacenes consisting of six-membered carbocyclic rings in the literature.175 As a result, researchers have been left to study these elusive systems using only theoretical models.

~~2.1.1.1 Semiempirical Studies and Aromatic Considerations~~

~~Early theoretical study of [n] cyclacenes was limited to low-level methods such as linear combination of atomic orbitals (LCAO), extended Htickel molecular orbital~~

(EHMO),176 and semi-empirical AMI methods1' to study properties such as frontier molecular orbitals (FMOs), Huckel aromaticity, geometry, and heats of formation. Since then, further insight into cyclacenes in terms of their electronic properties, geometry and stability has been gained.171

~~Since it is impossible to draw an aromatic sextet (Section 1.1.2.1) in any of the 99 carbocyclic rings of the [n] cyclacene backbone, the aromaticity of cyclacenes was~~

~~11Q strongly questioned by Ahiara in 1975. " Later, aromaticity and stability of~~

[n]cyclacenes were described with Hiickel's rule of aromaticity.179'180 The electronic structures of D„h symmetric (HF/STO-3G optimized) [n] cyclacenes (n = 3-5) was analyzed with extended Hiickel MO theory by Johnson and coworkers.176 Their study indicated a reduction in strain energy and pyramidalization of K bonds as a function of increasing n, suggesting greater stability for larger [n]cyclacenes. Early AMI models further suggest that the cyclization of acenes to the corresponding cyclacenes would be a highly endothermic process.177

~~2.1.1.2 DFT Geometries and Electronic Configuration~~

~~Geometrically, cyclacenes have been regarded as weakly interacting Schleyer~~

"trannulenes"181 (e.g. [20]trannulene, Figure 2.4 (a)), which are "all-trans cyclic polyene ribbons".182'183 Based on (U)B3LYP/6-31G* density functional theory (DFT) calculations for closed-shell singlet and open-shell triplet states, Houk and coworkers183 stated that geometrically, cyclacenes can be thought of as two fully delocalized polyacetylene ribbons with no peripheral (zigzag) bond alteration, joined by long single bonds and very weak 7i interactions. The long bonds connecting two ribbons get shorter with more parallel ribbons, such as in the case of graphite183 where all bonds are nearly the same length (~1.40A). This bonding arrangement explains reduced aromaticity and increased trannulene conjugation along the peripheral edge in the cyclacene systems.175 A detailed analysis of variations in bond geometries of M06-L optimized, D„h symmetric 100 [n] cyclacenes with respect to n shows that the transannular C-C bond (parallel to the principal axis) increases as a function of its radius (Figure 2.4 (b)).184 In a different study conducted by Chen and coworkers, D„h symmetric [ri] cyclacenes optimized to an open- shell (OS) singlet state have shorter transannular C-C bonds (Figure 2.4 (b)) than those of the triplet state.185

~~Principal axis~~

Analysis of the ground state electronic configuration of [ri] cyclacenes has also been evaluated by DFT methods. Houk's initial analysis in 2001 indicated a decrease in the singlet-triplet energy splitting with the increase of n, where the triplet ground state is favored for polyacenes and cyclacenes with nine or more fused benzene rings.183 Chen and coworkers - more accurately modeled this system by examining singlet electronic ground states of cyclacenes using UB3LYP/6-31G* with unrestricted spin properly implemented. From this study, OS singlet ground states of [ri] cyclacenes (n > 6) are predicted to be the lowest energy electronic configuration (Table 2.1).185 When n = 4 and

~~5, [n]cyclacenes assume a closed-shell (CS) singlet ground state that is lower in energy than the triplet state and equal in energy to the OS singlet state (Table 2.1).~~

101 n (even) Sos Scs T 4 0 0 36.6 5 0 4.1 4.1 6 0 8.0 6.8 7 0 7.5 12.1 8 0 7.3 7.9 9 0 16.6 14.1 10 0 8.9 10.5 11 0 24.3 17.9 12 0 12.3 14.3 13 0 30.9 31.1 14 0 16.9 19.2 Table 2.1: Relative ground state energies (kcal/mol) of [n]cyclacenes in their open shell 185 singlet (Sos), closed shell singlet (Scs) and triplet (T) states.

~~2.1.1.3 Unique Properties for Odd and Even [nlCyclacenes~~

~~Some notable trends have been observed for [n]cyclacenes related to whether the values of n are even or odd. Kim and coworkers claimed that [n]cyclacenes (for n = 6-~~

~~14) have unusual magnetic properties with more negative magnetic susceptibility, % (i.e., more diamagnetic character) for even values of n than for odd values (Figure 2.5).] 2~~

Also, x of [ri] cyclacenes decreases dramatically with the increase of n for even values while it stays nearly constant when the value of n is odd. This idea of antiferromagnetic properties in [n]cyclacenes has been considered further by other researchers. Houk and coworkers noted that the localization of the spin character on carbon atoms bearing hydrogen in [ri] cyclacenes is consistent with antiferromagnetic coupling that is also observed in zigzag-edged graphene nanoribbons,187 higher acenes (Section 1.1.2.4) and rectangular polycyclic aromatic hydrocarbons.188'185

~~102 Figure 2.5: Magnetic susceptibility (%) of [«]cyclacenes vs. n. Inset: Table of the plotted data. 182~~

According to Houk, the localized spin character on the zigzag-edges of the cyclacene behaves chemically as a collection of "partial radicals." Significant polyradical character is observed for systems as small as [6] cyclacene, (this compares well with that of oligoacenes larger than hexacene) which implies that such ground-state OS singlets of

~~j Of~~

~~[n]cyclacenes should be reactive and unstable. Smaller [n]cyclacenes (n < 6) with CS singlet ground states are too strained to be good targets for synthesis.183~~

~~Higher accuracy analyses of [n]cyclacenes (6 < n < 12) have been conducted by~~

Cramer and coworkers184 where density functional theory (B3LYP and M06-L) was compared with multireference second order perturbation theory (CASSCF/CASPT2) which "handles the multiconfigurational character of potential bi- or polyradicaloid singlet states in a rigorous fashion." The results suggested that the singlet-triplet energy gaps of [rc]cyclacenes decrease, and polyradical character increases with respect to 103 the increase of n. This result is in agreement with Chen's prediction."^ A DFT comparison between B3LYP and M06-L with respect to total spin character values () was also conducted. It is evident from their analysis that there is less deviation of for [n]cyclacenes with odd values of n ( ~~values are ~5% larger than those calculated from M06-L), than for even values of n ( ~~values are -60% larger than those of M06-~~~~

L, for even n > 6) (Table 2.2). The discrepancy was explained by the fact that the two methods have different sensitivities towards contamination of higher spin states (e.g. quintet or heptet spin states) with singlet-triplet wave functions for even n.

~~n (even) M06-L B3LYP n (odd) M06-L B3LYP \ 6 0.95 1.16 7 1.64 1.66 8 0.88 1.28 9 2.11 2.22 10 0.99 ! 1.62 11 2 35 251 1 12 1.35 | 2.12~~

~~Table 2.2: Calculated values (unit less) of for BS DFT calculations on singlet [«]cyclacenes with the M06-L/6-3 lG(d) basis set.185~~

~~The highest occupied a and f> molecular orbitals of even ([8]cyclacene, Figure~~

2.6) and odd ([9]cyclacene, Figure 2.7) [rc]cyclacenes notably differ with respect to symmetry as calculated at the BS M06-L/6-31G(d) level. Regarding odd [ri]cyclacenes, the canonical HOMO and LUMO orbitals each are predicted to be doubly degenerate as depicted for [9] cyclacene in Figure 2.7. This is also believed to be due to a difference in spin contamination of molecular orbitals for even and odd [n]cyclacenes.

~~104 Figure 2.6: Highest occupied a (left) and P (right) orbitals of [8]-cyclacene at the BS M06-L/6-31 G(d) level./184]- Reproduced by permission of The Royal Society of Chemistry.~~

~~Figure 2.7: Degenerate pairs of highest occupied a (left) and P (right) orbitals of [9]- cyclacene at the BS M06-L/6-31 G(d) level. [184]- Reproduced by permission of The Royal Society of Chemistry.~~

~~2.1.1.4 Predicted Applications Based on Theoretical Study of Cyclacene~~

~~Since 1954, various prospective proposals have been made primarily as an~~

105 outgrowth of theoretical studies on the hypothetical cyclacene molecules.166 It has been predicted that cyclacenes would be useful synthons to synthesize nanotubes,171 molecular wires,169 and develop new molecular devices.189 Balaban speculated that the cavity inside a cyclacene could act as a host for molecular guests or metal atoms.179 Xu and coworkers envisaged non linear optical (NLO) responses from normal and Mobius cyclacenes.'9

~~More recently, their computation also predicted that nanotube electrides made of lithium doped and lithiated [5]cyclacene building blocks are also high potential candidates for~~

NLO applications.191 Kivelson and Chapman predicted that cyclacenes could have possible interesting properties including high-temperature superconductivity and ferromagnetism.192 Molecules having a belt-like or cage-like structure, including cyclacenes, are important for supramolecular chemistry and studies of molecular

~~193 recognition.~~

~~2.1.2 Past Attempts to Synthesize Cyclacene~~

~~Stoddart and coworkers attempted to synthesize [12] cyclacene 148 starting with the Diels-Alder reaction of a bisdiene 149 and a bisdienophile 150 to form kohnkene~~

(151, Scheme 2.1).I94 [12]Collarene 152, a partially hydrogenated cyclacene precursor, was synthesized following three subsequent steps of deoxygenation, dehydration and reduction of kohnkene. However, their efforts to prepare 148 from 152 employing various dehydrogenation reagents (e.g. Pd/C, DDQ, chloranil) under a variety of different conditions were not successful.

~~106 (i) (")~~

~~PhMe CH,C7^71 . » lOkbar A A~~

~~(iiiJTiCVLiAlHt/TIIF (iv) Ac20/HCl (v)Li/NH3/EtOH/Et;0~~

~~-0-~~

~~Scheme 2.1: Stoddart's attempt to synthesize [12]cyclacene 194~~

Cory and coworkers aimed to synthesize soluble [8]cyclacene 153 with four hexyl groups attached to it (Scheme 2.2).I95 They started with bisquinone 154 and tetramethylenetetrahydroanthracene 155 to synthesize the [8]cyclacene framework

~~156.196 However, they were unable to synthesize the corresponding fully conjugated hexyl-substituted [8]cyclacene 153.~~

~~107 o o~~

~~QH13 155 C6H13~~

~~Scheme 2.2: Cory's attempt to synthesize hexyl-substituted [8]cyclacene. I9",,1%~~

Schliiter and coworkers developed a supramolecular Diels-Alder trimerization reaction to form a [18]cyclacene framework (157, Scheme 2.3).197 They started by synthesizing a diene precursor 158 which was made from the dimer of cyclonona-1,2- diene and /^-benzoquinone in three steps. The diene precursor 158 was reacted with dibromo substituted dienophile 159 in a Diels-Alder fashion. The resulting dibromo intermediate was used to generate a benzyne derivative which was trapped in situ by furan to generate compound 160. Further reaction of 160 with tetracyclone, followed by deprotection and oxidation of the hydroquinone moiety, and a final thermolysis in refluxing toluene yielded an intermediate "diene-dienophile"l7S 161. The intermediate

1 *-)7 * underwent an oligomerization to produce a mixture in which the trimer 162 is in thermal equilibrium with the cyclized compound 157 which contains the [18]cyclacene skeleton (Scheme 2.3). Schliiter and coworkers also noted that heating of the oligomer

~~162 in decalin maximized the yield of the cyclic compound 157 up to 45% (analyzed by~~

~~NMR).197 However, conversion into the corresponding fully conjugated [18]cyclacene product was not achieved. 108 O W Ph^As^Ph (1) Tolune, Ph Ph reflux, 2d Br Toluene, 70 °C, 2d~~

~~gr (11) Furan, n-BuLi, Tolune (H) a) HC1, MeOH, CH2C12" R -60°C-RT OR' 60 °C, Id 159 160 b) DDQ, CH2C12 (m) Toluene, reflux, 60h;~~

~~= (CH2)6 50 °C, overnight~~

~~Scheme 2.3: Schluter's synthesis of a substituted [18]cyclacene derivative. 197~~

~~2.1.3 Using [601 Fullerene-Acene Chemistry to Prepare a Cyclacene~~

~~1 QR~~

[60]Fullerene can participate in many cycloaddition reactions. The [4+2] cycloadditions, or Diels-Alder reactions are among the most common. In Diels-Alder reactions involving [60]fullerene, dienes always add to the 6,6 junction of the fullerene cage in a regioselective fashion. One example would be the reaction of [60] fullerene with o-quinodimethane 163 to form a [60]fullerene adduct 164 reported by Mullen and coworkers as shown in Scheme 2.4 200

~~Br Br 163~~

Scheme 2.4: [60]Fullerene adduct of o-quinodimethane. 109 Acenes also react similarly to form the corresponding [60] fullerene monoadducts shown in Figure 2.8. The [60]fullerene-anthracene monoadduct 165 synthesized by refluxing anthracene and C60 was first reported by Schliiter and coworkers.201 A

[60]fullerene-tetracene monoadduct 166 was synthesized using high-speed vibrational milling by Komatsu and coworkers." A C2V [60]fullerene-pentacene monoadduct 167 was prepared by refluxing pentacene and Ceo in toluene by Miller and Mack.203

Miller and Mack204 first observed that, if the central 6,13-positions of the pentacene are blocked by phenyl groups, the bis[60]fullerene adduct 168 of 6,13- diphenylpentacene is formed (Scheme 2.5). In the reaction, a cis isomer was the dominant product instead of both cis and trans, due to a favorable 7i-7t stacking interaction between the [60]fullerenes. X-ray crystal structures205 showed that the two

~~[60]fullerene moieties of the cis isomer were within the van der Waals distance (3.07 A ).~~

~~The cis stereoselective geometry was accurately modeled using the MM2 force-field method.206~~

~~110 6,13 -Diphenylpentacene~~

~~Scheme 2.5: Synthesis of bis[60]fullerene adduct 168 of 6,13-diphenylpentacene by Miller and Mack.204~~

~~Following the same concept of the 71-71 stacking interaction among the~~

~~[60]fullerenes, Miller and Briggs207 also synthesized a cw,c^-tris[60]fullerene adduct~~

169 of 6,8,15,17-tetraphenylheptacene. Thus, tetraphenylheptacene was generated in situ from 5,7,9,14,16,18-hexahydro-6,8,15,17-tetraphenylheptacene and DDQ, and subsequently reacted with excess [60]fullerene (Scheme 2.6).

~~tetrapheny lhepta cene~~

~~Scheme 2.6: Synthesis of as,c/s,-tris[60]fullerene adduct, 169 by Miller and Briggs.21~~

~~The addition of [60] fullerenes to large acenes results in the bending of the acene backbone because of the aforementioned cw-diastereoselectivity. Miller's group was~~

~~111 interested in synthesizing larger acene backbones so that the ends of the corresponding~~

[60]fullerene-adducts would be within the range of chemical bond formation. This could potentially be used to form a cyclacene framework. Finally, a retro Diels-Alder reaction of the [60] fullerene substituted cyclacene framework may yield phenyl substituted cyclacenes (Figure 2.9). Thus, soluble single walled nanotubular compounds (SWNCs) with controlled uniform dimensions (according to the size of the acene backbone) could be synthesized by the iterative coupling and oligomerization of substituted cyclacene

~~(Figure 2.9).i69 However, [60]fullerene adducts of simple phenyl substituted acenes larger than heptacene have yet to be realized.~~

~~Monomer Cyclacene, 1.3 nm~~

~~Dnii-r. 2 (•> nil IcnaiiK'i. ?.2 :nn~~

~~Octamer, 10.4 nm~~

~~Figure 2.9: (a) Earlier proposal for synthesis of a phenyl-substituted -cyclacene via closure of pentakis[60]fullerene adduct; (b) iterative coupling of cyclacenes to produce SWNCs.169~~

~~112 2.2 RESULTS AND DISCUSSION~~

~~2.2.1 Supramolecular Approach Towards the Synthesis of Cyclacenes~~

Given the accessibility of pentacene derivatives as compared to larger acenes, a new supramolecular approach to the construction of the cyclacene framework utilizing an end-functionalized bis-fullerene pentacene adduct was devised. Similar to Schliiter's approach197 to form the [18]cyclacene framework, 157 (Scheme 2.3), the cis bis-

~~[60]fullerene adduct of a 2,3,9,10-substituted 6,13-diphenylpentacene is geometrically predisposed to form hexaphenyl[24]cyclacene 170 via a cyclo-trimerization sequence~~

~~(Figure 2.10).~~

~~Figure 2.10: Proposed path for synthesis of phenyl substituted [24]cyclacene.~~

~~Our first aim was to synthesize a bis[60]fullerene adduct of diphenylpentacene~~

(Figure 2.10 (a)) with appropriate functional groups at the terminal rings (i.e. at 2,3,9,10- positions of the pentacene), which would be easy to tie together using a suitable linker. In our methodology, we first considered an Aldol-condensation for intermolecular cyclization to synthesize hexa-[60]fullerene adduct 171 (Figure 2.10). For this purpose, the bis[60]fullerene adduct 172 of 6,13-diphenylpentacene with four aldehyde groups at the 2,3,9,10-positions was a target molecule. This could then be linked together to 113 synthesize 171 using 1,4-cyclohexadione. The adduct 172 could be synthesized via oxidation of the bis[60]fullerene adduct 173 of 2,3,9,10-tetrahydroxymethyl-6,13- diphenylpentacene. In turn, the C6o-adduct 173 could be synthesized by a deprotection of the Ceo-adduct 174 of benzyl protected 2,3,9,10-tetrahydroxymethyl-6,13- diphenylpentacene (Scheme 2.7).

~~Scheme 2.7: Retro-synthesis of the targeted bis[60]fullerene adduct 172.~~

The precursor of 174, pentacene 175 with benzyl-protected hydroxymethyl groups at the 2,3,9,10 positions, was successfully synthesized from a commercially available furan precursor in nine steps. The detailed synthesis of 175 is discussed in the next section.

~~2.2.1.1 Synthesis of 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenylpentacene~~

The first step in the synthesis of 175 involved was the deprotection of commercially available 3,4-bis(ethoxycarbonyl)furan which is not very stable under ambient conditions. The ethoxycarbonyl groups of the furan were reduced using LiAlH4 by refluxing in ether for seventeen hours to synthesize 3,4-bis(hydroxymethyl)furan 176,

~~114 similar to the procedure of Jenneskens and coworkers" (Scheme 2.8). The reaction was quenched very slowly with a saturated solution of NH4CI to obtain an isolated yield of~~

~~95%. This represents a significant improvement over the 30-40%) yield obtained when using dilute sulfuric acid." '~~

LiA1H EtOOC 4 HOH,C C6H5CH2Br 1 2 \^\ Et2Q, reflux V^ NaH, DMF ' V^\ 0 EtOOC Overnight, N2, * ^ N2, Overnight /k/ btUUC H0H2C (95%) ,^ (97%) I 177 176 OBn1" Scheme 2.8: Synthesis of 3,4-bis(benzyloxymethyl)furan 177.

As hydroxymethyl groups are prone to oxidation, compound 176 was protected by benzyl groups (Scheme 2.8). Following Rebek's procedure, °l sodium hydride was used for deprotonation of 176 in the presence of benzylbromide to synthesize 3,4- bis(benzyloxymethyl)furan 177 in 97%> yield (Scheme 2.8).

A Diels-Alder addition reaction between 177 and dimethylacetylenedicarboxylate was accomplished at 110 °C for one hour. After chromatographic purification using a mixture of hexane and EtOAc (70 : 30), the Diels-Alder adduct 178 (Scheme 2.9) was isolated (90%) as a thick orange oil.209 Aromatization of 178 produced 1,2- bis(methoxycarbonyl)-4,5-bis(benzyloxymethyl)benzene 179 in 90% yield. Rebek's method209 using of TiCU and LiAlH4 in THF did not work until triethylamine was added to the reaction mixture, a modification adapted from Wong and Hou" aromatization procedure. In fact, Rebek never isolated or characterized 179. In contrast, we isolated this new compound in 90%> yield, as a thick, yellow oil and characterized it by NMR spectroscopy. 115 Compound 179 was then reduced by refluxing with LAH in THF for 17 hours (in contrast to Rebek's procedure209 of stirring at RT for 15 minutes) to synthesize 1,2- bis(hydroxymethyl)-4,5-bis(benzyloxymethyl)benzene 180. After extracting the organic layer using EtOAc followed by triturating with hexane, 180 was isolated as a white solid in 70% yield.

~~OBn Me02C-C=C-C02Me k^t^COjMe TiCl4, THF, 0°C 177 ^ ToT LAH,Et3N,N2>>~~

~~>^ j*. Overnighwvernigrj t ( C02Me (70%) 180 OBn 179 OBn""" OH~~

~~Scheme 2.9: Synthesis of 180 from 177.~~

Compound 180 was then subjected to a Swern oxidation211 with oxalyl chloride in a mixture of DMSO and DCM to synthesize a new dialdehyde, 4,5- bis(benzyloxymethyl)-l,2-benzenedicarboxaldehyde 181 as a golden yellow solid in 87%o yield (Scheme 2.10).

~~Following a procedure similar to the synthesis of 6,13-pentacenequinone (Section~~

~~1.1.1.5),39 2,3,9,10-tetrakis(benzyloxymethyl)-6,13-pentacenequinone 16, a yellow solid with strong yellow fluorescence, was then prepared from 181 and 1,4-cyclohexadione.~~

~~The resulting quinone 182 has much better solubility than the parent 6,13-~~

~~116 pentacenequinone and hence was easily purified using a silica column chromatography with DCM as solvent.~~

Phenyllithiation of 182 in THF at -78 °C followed by overnight stirring at room temperature under argon yielded a light yellow solid as a crude product of 2,3,9,10- tetrakis(benzyloxymethyl)-6,13-diphenyl-6,13-dihydro-pentacene-6,13-diol 183. The crude product was used in the next step without further purification.

Aromatization of 183 was first attempted using KI and glacial acetic acid,204 but this method did not work. The NMR spectrum of the resulting product mixture was inconclusive but seemed to indicate generation of small amounts of quinone 182. We then used a different method to aromatize 183, namely HCl and SnCl2. In this way

~~2,3,9,10- tetrakis(benzyloxymethyl)-6,l3-diphenylpentacene 175 was prepared in 82%> yield as a blue-purple solid.~~

CH2Cl2,DMSO OBn 5%NaOH Et0H (COClk Et3N, -78°C V^Y ° 180 — Swern Oxydation ^CHO °<>0 lhr, (65%) OBn 181 (57%) OBn O 182 OBn PhLi, THF, -78°C Overnight, RT SnCl2, 0Bn Dioxane, OBn OBn 10MHC1 30 min OBn (82%) QBn 183 QBn

~~Scheme 2.10: Synthesis of the new end protected functionalized pentacene 175 via synthesis of new intermediates (181, 182 and 183).~~

117 Pentacene 175 is highly soluble in organic solvents and was characterized by H and 13C NMR spectroscopies and LDI mass spectrometry (with a strong molecular ion peak at 911 m/z). The experimental data from UV-VIS spectroscopy, electrochemistry

(cyclic voltammetry, Figure 2.11), and theoretical data of computational studies for 175 are summarized in Table 2.3. The solution of 175 in CHC13 showed strong, red fluorescence with A™ax values at 600 nm, 555 nm and 516 nm (604 nm, 558 nm and 518 nm in ODCB). Time-dependent UV spectra of 175 (Figure 2.12) illustrated that, in solution phase, this substituted pentacene is stable for less than an hour, with a half life

~~(ti/2) of 34 minutes in CHC13 (ti/2 = 33 minutes in ODCB). The optical band-gap (Eg(opt) =~~

~~1.99 eV) is almost the average value of the band-gaps calculated from electrochemistry~~

(Eg(CV) = 1.88 eV) and from DFT (B3LYP/6-311+G**//B3LYP/6-31G*) calculations (Egap is 2.16 eV), as shown in Table 2.3. The deviation of the calculated LUMO value from its experimental value is quite large (0.43 eV) compared to that for the corresponding

HOMO values (0.14 eV). Although 175 shows limited stability in solution, its high solubility and low HOMO-LUMO gap (based on UV-Vis and CV data) suggest that it could be useful for further processing and functionalization.

~~^aw£ tia Ee(°p») Ox.(cy) Red.tv) HOMO(cv) LUMO(„} E|,(CV) HOMOcal UJMOal *-gap (nm) (min) (eV) (mV) (mV) (eV) (eV) (eV) (eV) (eV) (eV)~~

600, 34 1.99 636 -1398 -4.921 -3.04 1.88 -4.78 -2.61 2.16 555, 516 Table 2.3: Experimental (UV-VIS and CV) and calculated physical properties of pentacene 175 including A™ax, ti/2, oxidation potential (Ox.) and reduction potential (Red.), energies of HOMO, LUMO and band gap (Eg(opt), Eg(cv) and Egap are listed.

~~118 4- 2 E^ 0% = 636 mV / 3- -1436 mV /l~~

~~2- 600 mV / ^—'/ 1 1-~~

~~0- 13 o -1 - / f—-x / -1360 mV -2- / / 672 mV~~

~~-3- 2 F E^ Red = -1398mV -4-~~

~~1 I • I ' I ' I ' I ' I ' 1500 1000 500 0 -500 -1000 -1500 Potential (mV) Figure 2.11: Cyclic voltammetry of 175.~~

~~Figure 2.12: The time dependent UV spectra of 175 over 84 minutes.~~

~~119 2.2.1.2 Synthesis of Bis[601 Fullerene Adduct of 2,3,9.10-~~

~~Tetrakis(benzvloxvmethvf)-6,13-diphenylpentacene~~

A solution of pentacene 175 and a five-fold excess of [60]fullerene in CS2 was refluxed overnight to synthesize the bis[60]fullerene adduct 174 (Scheme 2.11) following a procedure established by Miller and Mack." Excess [60]fullerene and other byproducts were removed by column chromatography, and the product 174 was isolated in 20% yield.

~~Compound 174 is very stable under ambient conditions, and quite soluble in~~

~~J 13 DCM, CHC13, CS2 and ODCB, enabling facile acquisition of its H and C NMR spectra.~~

The ]H NMR spectra confirmed the preferential formation of C^ symmetric cis- diastereomer 174 over the corresponding C^ Jrarcs-diastereomer. The five :H signals detected for cis- 174 in the aromatic region are indicative of slow rotation of the phenyl groups on the NMR time scale, whereas the corresponding C2h trans isomer would show only three lH peaks for the phenyl substituents. Furthermore, mass spectra of 174 shows separate molecular ion peaks of [60]fullerene and 175, probably because fullerene- pentacene bonds are easily broken through a retro Diels-Alder reaction. Unfortunately, the average isolated yield of the reaction was only 10-20% (in contrast to 85% as reported in the literature for other [60]fullerene-pentacene adducts).204 The same reaction was also performed for shorter times and in ODCB at a higher temperature (100 °C).

~~However, the yield did not improve, possibly because the large benzyloxymethyl groups at the 2,3,9,10-positions of 175 hinder the approach of [60]fullerenes.~~

~~120 Scheme 2.11: Synthesis of bis[60]fullerene adduct 174 from 175.~~

~~2.2.1.3 Synthesis of Bis f601 Fullerene Adduct of 2.3.9.10-tetraiodomethvl-6,13-~~

~~diphenylpentacene~~

~~Benzyl deprotection of bis[60]fullerene pentacene adduct 174 was attempted to synthesize hydroxymethyl bis[60]fullerene pentacene adduct 173 according to Scheme~~

~~2.7. The hydrolysis procedure of Jung and Lyster212 to prepare alcohols by treatment with trimethylsilyl iodide (TMSI) from the corresponding ether was carried out as described in~~

~~Scheme 2.12.~~

~~R-O-R' + Me3SiI - R-0-SiMe3 + R'-0-SiMe3 + R'l + RI~~

~~,. H20 ROH + R'OH Scheme 2.12: Synthesis of alcohols from corresponding ethers using TMSI.212~~

Due to the limited supply of C6o-adduct 174, a 10 - fold excess of TMSI was used for benzyl deprotection under dilute reaction conditions in CDC13 for 15 minutes at room temperature. After the reaction, a dark brown solid of the bis[60]fullerene adduct of

~~121 2,3,9,10-tetraiodomethyl-6,13-diphenylpentacene, 184 (Scheme 2.13) was recovered in~~

~~48%» yield, instead of the desired deprotected adduct 173.~~

Compound 184 is not stable for long durations. Upon standing in solution phase, molecular iodine is observed to precipitate from the solution. Nonetheless, the dark brown solid of 184 was characterized with lK and 13C NMR spectroscopies ((a) and (b) in Figure 2.13). The lH spectrum of 184 sows five well resolved signals (two doublets and three triplets) in the region of 7-8 ppm, characteristic of the phenyl groups of the cis isomer of 184 with C2v symmetry (see appendix for expanded spectrum). The singlet at

~~5.66 ppm in the lH NMR spectrum and the peak at 2.81 ppm in the 13C NMR spectrum confirmed the existence of the corresponding iodomethyl groups of the adduct 184.~~

~~Scheme 2.13: Synthesis of bis-C6o adduct 184 of 2,3,9,10-tetraiodomethyl-6,13- diphenylpentacene.~~

~~122 Figure 2.13: (a) !H and (b) 13C of 184.~~

According to Jung and Lyster212 the corresponding alkyl iodides (Scheme 2.12) and hexamethyldisiloxane can be produced from the reacted dialkyl ether, if the alkyl trimethylsilyl ethers (Scheme 2.12) are allowed to react with excess TMSI at an elevated temperature (50 °C) for longer periods of time. Hence, we think that the use of excess

~~TMSI combined with slightly longer reaction times (15 minutes) instead of six minutes,212 led to the formation of the iodo-substituted compound 184 instead of 173.~~

~~However, since iodine is a good leaving group in general, the iodo-substituted~~

~~[60]fullerene adduct 184 could be amenable to a cyclization in the following step.~~

~~123 2.2.1.4 Towards the Synthesis of [241 Cyclacene~~

Several bicyclo compounds synthesized via Finkelstein reactions followed by in situ nucleophilic substitutions, were reported by Kost and coworkers 213 For example, a mixture of 2,3-bis(bromomethylnaphthalene), 2,5-dicarbethoxy-l,4-cyclohexanedione

~~185, K2C03 and Nal in acetone was refluxed to synthesize bicyclo compound 186~~

Scheme 2.14 (a). In this reaction, 2,3-bis(iodomethylnaphthalene) is produced in situ following the Finkelstein reaction as described in Scheme 2.14 (b).214 At the same time, the acidic alpha protons of 185 were deprotonated by K2C03 producing an enolate anion that reacted with the iodomethyl groups via nucleophilic substitution Scheme 2.14 (c).

~~The electron-withdrawing groups (-C02Et) attached to 185 enhance the acidity of the alpha protons and direct the regioselectivity of the nucleophilic substitution.~~

~~CH2Br C02Et K2C03, Nal + C02Et CH Br Et0 C Acetone, reflux, 2 2 24 h, (38%) Et02C~~

~~CH2Br Nal~~

~~rii R Acetone, reflux, ^^ 45 min, (85%)~~

~~Scheme 2.14: Coupling reaction through nucleophilic substitution. In step (c)~~

~~124 iodomethylbenzene and 1,4-cyclohexanedione are shown for clarity.~~

~~Following Kost's procedure, an ODCB solution of the tetraiodomethyl~~

[60]fullerene adduct 184 (11.9 mg) and 1,4-cyclohexadione was heated to 60 °C in the presence of K2C03. Since 184 is neither very stable nor soluble in acetone, the reaction was performed in ODCB at a lower temperature. There was no observable change within two hours; but, as soon as two drops of DBU (l,8-diazabicyclo(5.4.0)undec-7-ene, a strong base) were added, a light brown colored suspension was formed. After stirring overnight and working up, a brown solid was recovered. The solid has extremely poor solubility in most of the common organic solvents and only a [60] fullerene peak was detected in the corresponding LDI mass-spectra.

Since the yield of 184 was low, we decided to study model-reactions with different conditions first, and then apply those conditions in the final step. For all the model-reactions, 1,2-diiodomethylbenzene 187 was chosen as our model for the

[60]fullerene adduct 184. Bearing in mind that 184 has limited solubility (good in ODCB and CS2, less soluble in toluene) and low stability, all of the model-reactions were performed in either ODCB, CS2 or toluene at relatively low temperatures (between RT and 60 °C).

~~2.2.1.4.1 Model Reaction with 1,4-Cyclohexanedione~~

1,2-Diiodomethylbenzene 187 was treated with 1,4-cyclohexanedione with varying conditions as shown in Scheme 2.15. Several trials were performed using K2C03 or DBU as base, with or without 18-crown-6 (a phase transfer catalyst) either in ODCB 125 or in toluene at various temperatures (RT-60 °C) for different lengths of time (lhour to 24 hours) to synthesize either octahydropentacenequinone 188 or hexahydroanthracenequinone 189. In most cases, the starting materials were recovered, implying that this procedure was not suitable for use with 184.

~~K2C03 or DBU + ODCB or toluene OR 18-crown-6 u CH,I RT-60 °C 187 lh-24h O 188 189~~

~~Scheme 2.15: Model reaction with 1,4-cyclohexanedione.~~

~~2.2.1.4.2 Model Reaction with 1,4-Pflra-Benzoquinone~~

Our next attempt was to try the Diels-Alder reaction of 187 with 1,4-para- benzoquinone in the presence of KI in DMF, following a procedure similar to the synthesis of 6,13-pentacenequinone (Section 1.1.1.5).39 We also tried the same reaction in the presence of one equivalent of [60] fullerene to check the reactivity of 187 towards

[60]fullerene. In the absence of [60]fullerene, we were able to synthesize our desired product 6,13-pentacenequinone (Scheme 2.16 (a)). In the presence of [60]fullerene, however, we observed formation of 164 (Scheme 2.16 (b)) suggesting an o- quinodimethane intermediate that is known to have high reactivity towards [60] fullerene as described above (Section 2.1.3). This result implied that these conditions are not useful for the desired cyclization of 184 due to interference from [60]fullerene.

~~126 O O~~

~~-a:: KI, 18-crown-6 187 ODCB, 2d, 110 °C~~

~~o O (b) 187 + C 60 KI, 18-crown-6 ODCB, 2d, 65 °C~~

~~Scheme 2.16: Model reaction with 1,4-para-benzoquinone.~~

~~2.2.1.4.3 Model Reaction with Catechol~~

Trahanovsky and coworkers reportedj21 5 the synthesis of 6,11-dihydro- dibenzo[b,f][l,4]dioxocin 190 upon heating a mixture of 1,2-dichloromethylbenzene, anhydrous K2C03 and catechol in DMF. Modifying their method by using 187 and 18- crown-ether in ODCB, we were able to synthesize 190 as a white solid (Scheme 2.17).

~~Despite its poor solubility, 190 was fully characterized by :H and 13C NMR spectroscopies. Unfortunately, the poor solubility of 190 discounted the viability of this method for the cyclization of 184.~~

~~£>H~~

~~.CH2I OH s=0 ^^CH2I K C0 , 18-crown-6 2 3 190 187 ODCB, 50 °C 17h,48%~~

~~Scheme 2.17: Model reaction with catechol.~~

~~127 2.2.1.4.4 Model Reaction with 1,4-Benzenediamine and Derivatives of 1,4-~~

~~Benzenediamine~~

~~Various reports suggest that 2-phenylisoindoline 191 can be synthesized from~~

~~aniline and 187 using different conditions.216 We synthesized 191 by the reaction of 187~~

~~and aniline using K2C03 and 18-Crown-6 in ODCB at 60 °C (Scheme 2.18 (a)).~~

~~Compound 191 formed in excellent crude yield (98%) and was characterized by NMR~~

~~spectroscopy and mass spectrometry. rrCH21 H2N^ rrvo ^TH2I KjCO^l8-Crown-6 ^^ ^-* 187 ODCB, 60 °C, 17h 191 (98%) Scheme 2.18: Model reaction with aniline.~~

~~We were also able to synthesize new compound 192 when 187 was reacted with~~

~~1,4-benzenediamine (Scheme 2.19). Due to poor solubility, it was difficult to achieve an~~

NMR spectrum of 192 with adequate signal to noise ratio. Nonetheless, 192 could still be characterized by mass spectrometry. We also performed the same reaction in the presence of [60] fullerene to check for possible side reactions, if any. However, no significant change in the result was observed upon the addition of [60]fullerene.

~~^^ CH2I K2C03,18-Crown-6 187 ODCB, RT-60 °C, 192 17h, (60%) Scheme 2.19: Model reaction with 1,4-diaminobenzene.~~

128 As the solubility of 192 was very low, we then tried the same reaction with diaminodurene (2,3,5,6-tetramethyl-l,4-benzenediamine) and ^//-diaminobiphenyl as described in (a) and (b) in Scheme 2.20, respectively. However, in both cases the solubilities of the new compounds 193 and 194 were poor. Thus, they were only characterized by LDI mass spectrometry.

~~H2N^ ^NH2 OC°H21———- ULMJ^ ^TH2I K2C03, 18-Crown-6 ^^V "Mf 187 ODCB, RT-60 °C, 193~~

~~^1/1/^ ^^\ 7=\ 7=\ (b) 18? K2C03, 18-Crown-6 " KJ^y^'^J^J^^ ODCB, 50-70 °C, 194 17h, (95%) Scheme 2.20: Model reaction with (a) diaminodurene and (b)/\p'-diaminobiphenyl.~~

Since solubility is expected to be one of the main issues for characterization of any cyclacene or related structure, we planned a different synthetic scheme to synthesize highly soluble diamino compounds by introducing longer alkyl chains at the 2,3,5,6- positions of the benzene ring of 1,4-benzenediamine, as shown in Scheme 2.21. In this regard, we were able to brominate dinitrodurene by refluxing it in CHC13 with NBS and

~~AIBN in the presence of light. New compound l,2,4,5-tetrakis(bromomethyl)-3,6-dinitro- benzene 195 was characterized by NMR spectroscopy and LDI mass spectrometry.~~

~~However, we were not able to synthesize the dinitro compound 196 in the subsequent~~

~~step using either alkylthiol or long chain alcohol under different reaction conditions 129 (including numerous bases at various temperatures) as reported for similar reactions.""~~

~~Thus, the synthesis of the diamino compound 197 and its reaction with 184 remain unfinished.~~

~~N02 N02 NBS, AIBN, CHCl3Br^^pBr ^^ Reflux, 3d, (34%) Br^^^^Br " "Jr HOc"^^~~

~~N02 195 N02~~

~~N02 xH, .s.n.a?. #x' xff HCl ^X^^V^X. Ml 1 17 N02 " 197 NH2 196 (X = S or O) Scheme 2.21: Attempted synthesis of highly soluble octadecyl substituted diamino benzene 197.~~

~~2.2.1.4.5 Model Reaction with 1,2,4,5-Benzenetetramethanethiol~~

~~We also considered the cyclization of 184 using 1,2,4,5-benzenetetramethanethiol~~

~~198 to form more flexible non-aromatic ten membered rings as linkers, similar to the synthesis of thiacyclophanes by Hanton and Sikanyika. 8~~

In a model reaction 5,7,12,14-tetrahydro-dibenzo[c,h][l,6]-dithiecin 199 was synthesized in70%> yield by combining 187 with 1,2-benzenedimethanethiol 200 using the weak base potassium fluoride (KF) in DMF, following the procedure of Miyawaki and coworkers.219 In order to establish the reaction condition more suitable for our ultimate goal, we were also able to synthesize 199 using a modified method involving

~~ODCB solvent and 18-Crown-6 at either room temperature or 50-60 °C (Scheme 2.22). 130 rvCH21 KA^m 54 tr -r s~~

~~^CH2I KF, 18-Crown-6 ^^^S 187 ODCB, 2h, RT 199 40% Scheme 2.22: Model reaction with 1,4-diaminobenzene~~

Compound 198 was then synthesized in two steps from durene involving the reaction between l,2,4,5-tetrakis(bromomethyl)benzene 201 and thiourea according to the procedure of Otsubo and coworkers (Scheme 2.23).22u Compound 201 was synthesized by the bromination of durene using NBS.

~~Br Br SH SH~~

~~NBS if^T ® (NH2)2SO, ethanol, 6h, reflux~~

~~CHC13, 17h F^^F (ii) H20; H2So4; 6h; reflux (60%) Br Br (55o/o) SH SH 201 198 Scheme 2.23: 1,2,4,5-benzenetetramethanethiol 198.~~

Tetrathiol 198 was reacted with bis-[60]fullerene adduct 184 using same procedure (Scheme 2.22) established to synthesize 199. An insoluble brown solid that was difficult to characterize was recovered (Scheme 2.24).

~~SH KF,18-Crown-6 ODCB, !7h,RT ^ Brown insoluble solid~~

~~*** 184 >*~~

~~Scheme 2.24: Reaction of bis [60]fullerene adduct 184 with 198.~~

~~131 2.2.2 Theoretical Study of Substituted Cyclacenes~~

To help improve our understanding of the physical properties of functionalized and unfunctionalized cyclacenes, we performed preliminary DFT calculations. Before selecting DFT, it was necessary to compare the merits of available and feasible computation methods suitable for studying the stability and electronic properties of larger and/or functionalized cyclacene structures. Cramer's preliminary studies184 of cyclacenes and CNTs (Section 2.1.1) provided some guidance to available methods. However, their multi reference method was beyond the scope of this study.

~~2.2.2.1 Evaluation of Methods using flOlCyclacene~~

~~To ensure agreement with established results, " [10] cyclacene 147 was chosen first as a test molecule. In order to evaluate the various computational methods,~~

~~[10]cyclacene was first optimized separately with a semi-empirical (PM3) method as well as with a DFT (B3LYP/6-31G*) method. The SPE, HOMO and LUMO energies and~~

2 respective gap (Egap), and the expectation value of total spin (~~) of the cyclacene were computed using unrestricted broken-symmetry single point energy calculations that employed both 6-31G(d) and 6-311+G(d,p) basis sets, separately, for comparison (Table~~

~~2.4).~~

~~All the calculations show close agreement (within 0.03% deviation) of the SPE values of [10] cyclacene when compared to those reported by Chen and coworkers (Table~~

2.4, Obs. 3). However, the total spin expectation values are found to be method dependant. The values of b before annihilation of the first spin contaminant of 132 [10]cyclacene varies as a function of basis set (9%>) and geometry optimization (~1%>), with respect to the reported values (Table 2.4, Obs. 3, e.g. 6% (for UB3LYP/6-

~~311+G**//PM3 for obs. 2) and 9% (for UB3LYP/6-311+G**//B3LYP/6-31G* for obs.~~

~~4)). This deviation for a after annihilation of the first spin contamination further increases up to 15%, when the calculation was performed using the triple-zeta basis set~~

(Table 2.4, Obs. 4). Moreover, irrespective of different HOMO and LUMO energy- values associated with [10] cyclacene, Egap is found to be almost the same (~2 eV) for all cases. It is also noticed that regardless of the method used for geometry optimization of

[10] cyclacene (semi-empirical vs. DFT), all the calculated values for different observations mostly depend on the basis set (6-31G* vs. 6-311+G**) used for SPE calculation (Table 2.4). Despite the apparent accuracy of the PM3 optimization relative to B3LYP/6-31G* for [10] cyclacene, it gave inconsistent results with the addition of substituents. As a result, further studies were conducted using UB3LYP/6-

~~311+G**//B3LYP/6-31G*.~~

2 b 2 a Obs. SPE//Opt. Energy HOMO LUMO gap (singlet) (eV) (eV) (eV) (eV) 1 UB3LYP/6-31G* -41797.9 1.67 5.21 -4.21 -2.22 1.99 //PM3 (0.002%) (1.21%) (0.97%) 2 UB3LYP/6-311+G** -41807.31 1.55 4.62 -4.58 -2.68 1.9 //PM3 (0.020%) (6.06%) (10.47%) 3 UB3LYP/6-31G*// -41798.87 - - - 1.65 J. 16 B3LYP/6-31G* 4 UB3LYP/6-311+G**// -41808.22 1.5 4.36 -4.77 -2.88 1.9 B3LYP/6-31G* (0.022%) (9.09%) (15.50%) 2 Table 2.4: The SPE, HOMO, LUMO energies, the HOMO-LUMO gap (Egap) and values beforeb and after3 annihilation of the first spin contamination for [10] cyclacene. Observation 3 taken from Chen and coworkers.18:> Parenthetical percentages are percent deviation with respect to obs. 3.L'5

~~133 2.2.2.2 Theoretical Studies for Substituted [lOlCyclacenes and [181Cyclacenes~~

Although, hexaphenyl substituted [24]cyclacene 170 was the final target for our synthesis (Figure 2.10), the absence of reported studies beyond [14]cyclacene, suggested a smaller molecule should be considers. Because the minimum number of carbocyclic rings needed to build a cyclacene from three pentacene backbones connected through three additional six membered rings is 18, we choose [18]cyclacene 202 and hexaphenyl substituted [18]cyclacene 203 for computational studies (Figure 2.14). Based upon our knowledge93116118 of enhancing acene stability through the use of alkylthio or arylthio substituents, hexamethylthio[ 18]cyclacene 204 and hexaphenylthio[ 18]cyclacene 205 were also considered. Thio-substituted [10] cyclacenes including 1- phenylthio[ 10] cyclacene 206, 1,1 l-diphenylthio[ 10] cyclacene 207 and decaphenylthio[ 10]cyclacene 208 were also considered for comparison (Figure 2.14).

~~HOMO and LUMO energies, the associated gaps (Egap) and the expectation value of total spin () of various cyclacenes with optimized geometries at the B3LYP/6-~~

~~31G* level and unrestricted broken-symmetry single point energies calculated using the~~

~~6-311+G(d,p) basis set are listed in Table 2.5.~~

134 >*. J*tr. •ttf'&ifo w**v m*m "—•»,# ~ifa.f '.*/- 1-phenylthio 1,11-diphenylthio 1,3,5,7,9,11,13,15,17,19- [10]cyclacene -[10]cyclacene -[10]cyclacene decaphenylthio[10]cyclacene 147 206 207 208 -•V ifr i *

^Jt „M *» jti is M **

«# Al *J *• Ji M*

~~E18]cyclacene ^ ^ 1,7,13,19,25,31- 1,7,13,19,25,31- lxil ,,,,-, hexamethylthio hexaphenyithio Hexaphenyl [18]cyclacene [18]cyclacene [18]cyclacene 203 204 205~~

~~Figure 2.14: B3LYP/6-31G* optimized cyclacenes.~~

~~It is apparent that cyclacene 203 with the most structural similarities to our targeted cyclacene 170, has an unusually high a value (12.22). In accordance with~~

Chen and coworkers,185 cyclacene 203 is thus predicted to be unstable given its substantial radical character. On the contrary, both sulfur substituted [18]cyclacenes 204 and 205 were found to have zero a values indicating no radical character. Hence, based on these calculations, cyclacenes 204 and 205 are expected to be more stable as compared to 203. Moreover, the HOMO-LUMO gaps for 204 and 205 are 58% lower than that of cyclacene 203 and 66%> lower than that of pentacene (Egap = 2.18). Thus, both 204 and 205 are viewed as promising targets.

~~135 Mol. Name HOMO LUMO F b a (eV) gap (eV) (eV) 202 [18]cyclacene -4.3 -3.54 0.76 0.2 0.04~~

203 1,7,13,19,25,31- hexaphenyl -4.67 -2.9 1.77 3.46 12.22 [18]cyclacene 204 1,7,13,19,25,31- hexamethylthio -4.31 -3.57 0.74 0.02 0 [18]cyclacene 205 1,7,13,19,25,31- hexaphenylthio -4.38 -3.64 0.74 0.01 0 [18]cyclacene 147 [10]cyclacene -4.77 -2.88 1.9 1.5 4.36

~~206 1 -phenylthio -[10]cyclacene -4.4 -3.35 1.05 0 0~~

~~207 1,11-diphenylthio -[10]cyclacene -4.46 -3.33 1.13 0.24 0.04~~

208 1,3,5,7,9,11,13,15,17,19- deeaphenylthio -4.76 -3.1 1.66 1.44 4.07 [10]cyclacene 2 Table 2.5: The HOMO, LUMO energies, the HOMO-LUMO gap (Egap) and ~~values beforeb and after3 annihilation of the first spin contamination, for respective cyclacenes using UB3LYP/6-31 l+G**//B3LYP/6-31G*.~~

~~It is also interesting to note that a single phenylthio substitution on [10] cyclacene~~

206 may theoretically improve the stability by reducing its spin character to zero, consistent with the general expectation of thio-substitution on acenes. Unexpectedly, cyclacene 207 with more than one thio- substituent has enhanced spin character and hence possibly it has decreased stability. Furthermore, cyclacene 208 with ten phenylthio substituents has an even larger a value with 99%> increase with respect to 207 with two phenylthio groups. As per this result, it can be inferred that there could be a limit of

~~136 thio-substitution of [ri] cyclacene to minimize the a values and minimize the radical~~

~~character for each value of n. Irrespective of length of the cyclacenes, however, lower~~

~~a values correlate with lower HOMO-LUMO gaps of the corresponding cyclacenes.~~

~~Additional DFT studies are required to solve triplet states and open-shell singlet states of~~

~~each cyclacene derivative studied here, for comparison.~~

~~2.2.3 Future Work to Synthesize Thio-functionalized Cyclacene~~

~~Based on indications from our theoretical data, we also started to synthesize 6,13-~~

~~sulfur-substituted end functionalized pentacenes from our previously synthesized pentacenequinone 182 using previously discussed synthetic procedures (Section 1.2.1).~~

~~For this purpose, we have planned to synthesize 6,13-pentacene-3,3'-bisthiopropanoic~~

acid 209 as shown in Scheme 2.25. The corresponding 6,13-dihydroxy compound 210 was synthesized by refluxing 182 in THF using NaBH4. The thio-substituted pentacene precursor 211 was prepared from 210 using either ZnBr2 or Znl2 in DCM. Subsequent

~~aromatization reactions to synthesize 209 have yet to be undertaken.~~

~~137 Scheme 2.25: Synthetic approach of thio-substituted pentacenes 209.~~

~~2.3 CONCLUSIONS~~

We reviewed predicted stabilities, HOMO-LUMO energies and electronic properties of unsubstituted cyclacenes based on theoretical studies. We also surveyed earlier attempts to synthesize various functionalized cyclacenes.

We proposed to synthesize phenyl substituted [24]cyclacene 170 via supramolecular assembly of c«-bis[60]fullerene adducts of a 2,3,9,10-substituted 6,13- diphenylpentacene. To accomplish this, we successfully synthesized target pentacene 175 as well as [60]fullerene adducts 174 and 184. However, a trimerization of 184 to a

~~[24] cyclacene precursor has yet to be achieved.~~

To complement our synthetic approach, we also performed preliminary calculations for unsubstituted and substituted cyclacenes using unrestricted DFT calculations. Based on our results it can be predicted that there may be a limit of thio- substitution of [ri] cyclacene to minimize the ~~values and minimize the radical character for each value of n. 138 CHAPTER 3~~

~~3. C60 AND CNT CHEMISTRIES~~

~~3.1 INTRODUCTION~~

~~3.1.1 Allotropes of Carbon - [601 Fullerene and Carbon Nanotubes~~

Carbon, due to its very unique chemical bonding, can exist in various stable allotropic forms. Diamond and graphite are two naturally occurring allotropes, while fullerenes and carbon nanotubes (CNTs) are produced artificially.

In 1984, mass spectrometry evidence of nanostructured canbons (C6o) was first observed by Rohlfing and coworkers during their study of carbon clusters formed from graphite using pulsed laser vaporization." However, the closed cage [60]fullerene

~~(truncated icosahedron) structure was first proposed in 1985 by Curl, Kroto and~~

Smalley,1'" for which they were awarded the 1996 Nobel Prize in chemistry. Only a minute quantity of Ceo was formed in Kroto's experiment, but Kratschmer, Fostiropoulos and Huffman soon thereafter discovered a carbon arc procedure to produce soot containing macroscopic quantities of Ceo, C70 and smaller amounts of larger fullerenes.222

~~Due to its resemblance with the geodesic structures created by the architect~~

~~Richard Buckminster Fuller, the molecule of C60 was first named as~~

~~"buckminsterfullerene". [60]Fullerene or C60 has a spherical cage-like structure with twelve isolated pentagons and twenty hexagons arranged to form a truncated icosahedron~~

~~139 as shown in Figure 3.1 (a).~~

The most common reaction of [60]fullerene is a 1,2 addition reaction across the bonds between two hexagons (i.e., a 6,6 bond). After addition of a first symmetric addend across a 6,6 bond, there are eight different bisadduct regioisomers that can form upon addition of a second symmetric addend at one of the other available 6,6 bonds. The corresponding isomers are typically named according to the nomenclature suggested by

~~Hirsch and coworkers (Figure 3.1 (b)).~~"'~~

~~(a) (b)~~

~~Figure 3.1: (a) Structure of [60]fullerene; (b) bisadduct nomenclature as developed by Hirsch.223~~

~~Carbon nanotubes (CNTs), on the other hand, are elongated, tubular macromolecules with a graphitic long-axis and hemispherical fullerene-like caped ends.~~

There are two main categories of carbon nanotubes, namely single walled carbon nanotubes (SWNTs) and multi walled carbon nanotubes (MWNTs). MWNTs were first discovered in 1991 by Iijima;m two years later SWNTs were independently observed by

~~Iijima224 and Bethune.225~~

140 SWNTs contain a single graphene sheet rolled into a cylinder with diameters that typically vary from 0.4 nm - 3 nm. ~ MWNTs consist of concentric cylinders of SWNTs with outside diameters varying from approximately 1.4 nm - 100 nm.226 The spacing between the concentric layers in a MWNT is about 0.34 nm which is similar to the interlayer spacing in graphite (Figure 3.2).

~~(a) (b) Figure 3.2: (a) single walled nanotube; (b) multi walled nanotube.~~

CNTs are known to be either metallic or semiconducting, depending on their diameters and spiral configurations (i.e., chiral winding angle). Based on the orientation of the rolling of a graphene sheet with respect to any arbitrary tube axis, nanotubes are classified into three categories: armchair, zigzag and chiral nanotubes (Figure 3.3). The varying configurations of nanotubes are distinguished by their chiralities which can be represented by a pair of integers (n,m) defining the tube's direction and diameter as per the two equations-" shown in Figure 3.3. Here, W is the diameter of the tube, 'a' is the

~~C-C bond length in the graphene sheet and '#' is the chiral angle of the~~ ~~carbon nanotube.~~

~~The three classes of CNTs have different electronic properties. For instance, armchair~~

~~141 nanotubes (n = m,6 = 30°) are metallic while zig-zag (m = 0, n > 0, 6 = 30°) and chiral (0~~

~~< \m\ < n, 0 < 6 < 30°) nanotubes are semiconducting.227~~

~~Figure 3.3: Images of (a) armchair, (b) zigzag and (c) chiral nanotubes, where chirality is defined by 6 and tube properties are defined by a combination of d and 6.~~

Since their discovery by Iijima in 1991,173 carbon nanotubes have been studied extensively because of their unique mechanical,"" thermal, electrical " ' and many other interesting properties. Polymer composites,2'' field-effect transistors and field- emission displays2'2 are among the many attractive areas of research for CNTs. Due to their unique properties, numerous ideas for applications of CNTs in various fields have been proposed including (1) electronics (i.e., wires, transistors, switches, interconnects, memory storage devices), (2) opto-electronics (i.e., light-emitting diodes, lasers), (3) sensors, (4) field emission devices (i.e., displays, microcopies), (5) batteries/fuel cells, (6) fibers, reinforced composites, and (7) catalysts.""

~~142 3.1.2 Physical and Chemical Properties of Can and CNTs~~

Ceo can be dissolved in several organic solvents including CS2 (7.9 mg/mL), o- dichlorobenzene (27 mg/mL) and toluene (2.8 mg/mL).23j Because it dissolves in solvents, chemical modifications of Ceo can be readily performed as applications demand.

Compared to fullerenes, however, direct solubilization of CNTs is much more challenging. In fact, suspensions rather than solutions of CNTs are typically sought. In suspensions, the CNTs are not present as individual tubes, but rather as collections or bundles involving relatively small numbers of tubes. There are two ways to make a suspension of the CNTs: (1) non-covalent-approach: CNTs can be dispersed in solutions with the help of surfactants (e.g. SDS)2'4 or through coating with polymers (e.g. polystyrene235), or (2) covalent functionalization: the tubes can be functionalized using a variety of typically harsh reaction conditions. These approaches work by disrupting attractive van der Waals interactions between tubes, essentially converting large particles composed of many tubes into smaller bundles.

[60]Fullerene can be chemically modified through hydrogenation, 6 redox chemistry (chemically^ or electrochemically '), photochemical reactions," nucleophilic240 and electrophilic additions,241 radical reactions,242 and cycloadditions - most commonly [4+2] Diels-Alder reactions (Section 2.1.3). Recent advances in

~~[60] fullerene chemistry show considerable potential for biological24"' and organic electronic (e.g., solar cell)244 applications.~~

~~The functionalization of CNTs include (i) end cap functionalization245 by oxidation using strong oxidizing agents such as nitric acid, sulfuric acid and hydrogen~~

~~143 peroxide to introduce carboxylic acid groups (-COOH) at the ends and at defect sites of~~

~~CNTs, and (ii) side wall functionalization such as hydrogenations,246 radical reactions,247 halogenations,248 alkylations,249 Friedel-Crafts acylations,250 arylations,251 addition~~

~~9S9 9S^ 9S4- reactions of nitrenes and carbenes, 1,3 dipolar cycloadditions and sylilation reactions.~~

A comprehensive review of chemistries appropriate for functionalization of C6o, larger fullerenes and CNTs is beyond the scope of this thesis. The interested reader is encouraged to locate literature reviews. "'' '"

~~3.1.3 Reactivity of C<;n towards Superacids~~

Miller and coworkers first reported the oxidation of electrophilic C6o by the reaction with fuming sulfuric acid (H2SO4.SO3) and chlorosulfomc acid (CISO3H) to produce sultonated (Figure 3.4) and chlorinated C60 adducts respectively.2^6 Fullerene radical cations form as intermediates in both reactions. With the help of different characterization methods such as FTIR, EPR, NMR and TGA, Miller and coworkers identified polysultones of C60 (C6o(S03)x) and chlorinated fullerene (C6oClx) as products of reactions run in fuming H2SO4 and CISO3H, respectively."5

~~Figure 3.4: Mono /?-sultone of C60, E = 700.33 Kcal/mol (PM3).~~

144 Cataldo first published a comparative study of electronic spectra of C6o, C7o and graphite in oleum (H2SO4.SO3) and triflic acid.258 According to this study, two characteristic bands for the radical cation of C60 (C6o+) in oleum occur at 930 nm and

~~1005 nm. The study also suggests that C60 is much more reactive towards oxidizing agent~~

~~(e.g., ozone) than C70.~~

Scharff and coworkers259 reported charge transfer complex of C60 (green colored solution formation), followed by the formation of C6o+ (yellow colored solution) depending on the increase in concentration of an oxidizer (SO3) in a superacid medium of oleum as well as in other superacid media such as HS03F.SbF5 (magic acid) and HSO3F.

Reed and coworkers reported the formation of stable HC6o+ and C60+ by the treatment of C60 with a carborane superacid, H(CBnH6X6) (where X = chlorine or bromine), whose conjugate base (CBuHeXe") is the exceptionally inert carborane anion.260

~~3.1.4 Reactivity of CNT towards Superacids~~

Dispersing SWNTs in various superacids is a common technique to solubilize them via direct protonation. Davis and coworkers first reported the dispersion of SWNTs up to 10 wt%> in different acids including H2SO4 with varying concentration of excess

~~SO3, chlorosulfomc acid and triflic acid/61 They found a novel type single phase nematic liquid crystal formation at sufficiently high concentration of SWNTs (~3.5 wt%) in 102%>~~

~~H2S04(with excess S03).~~

145 Ramesh and coworkers found that the liquid crystalline mesophase is preserved in the solid state of SWNT aggregates even after the removal of superacids.262 Ramesh and coworkers also demonstrated that diameter selective separation of SWNTs is possible by tuning the direct protonation sensitivity of SWNTs in CISO3H via addition of a non- superacid (methane sulfonic acid).26"'

Very recently, Davis and coworkers presented and explained a complete experimental phase diagram of SWNTs in different superacids and found that stronger acids yield a larger liquid-crystalline domain and more uniform fibers and films. 6

~~3.1.5 CNT Interactions with Latex Particles~~

The use of latex technology to exfoliate and disperse CNTs in a polymer matrix is a new but versatile, reliable and environmentally friendly approach that allows the production of conductive composites of CNTs.265 Wei and coworkers used this new technique of self-assembly of polystyrene (PS) latex particles and SWNTs in a FET to increase the electric field at the metal-CNT contact and thus transformed the conventional unipolar SWNT-FETs into ambipolar devices with improved gate capacitance. 66

Jurewicz and coworkers used plasticized colloidal latex particles (based on random copolymerization of butyl acrylate (BA), methyl methacrylate (MMA), and methacrylic acid (MAA) with particle size of 270 nm) as a template for the self-assembly of CNTs into ordered, three-dimensional networks. After releasing the latex particles, the

~~CNTs still retained the high conductivity within the networks/1. Similar SWNT-latex~~

~~146 based nano-composites using different latex beads have also been described in various other reports."~~

Over the past few years, considerable research has also been performed using both pristine and functionalized MWNTs to produce latex-MWNT based nano- composites.269 Castano and coworkers demonstrated the introduction of H-bonding interactions among monodispersed polystyrene latex nanoparticles with carboxyl- terminated groups (PSNC) and carboxyl-terminated functionalized MWNTs to produce stable nano-composites.270 A TEM image of the nano-composites is shown in Figure 3.5.

Paunov and coworkers reported the production of micro-structured hollow shells of MWNTs by self-assembling amino functionalized MWNTs (NH2-MWNT) and sulfate-polystyrene latex particles, followed by the dissolution and removal of latex particles using toluene.2 ' Uniform and spherical SEM images of the nano-composites before and after the dissolution of PS particles are shown in Figure 3.6.

~~147 __^ 1) Ultrasound 2) Oiluts with 3% HCl (oq) ' «* \\ j Mfott j 3) Cross-link CNT with glutwaM«hy~~

~~148 3.2 RESULTS AND DISCUSSION~~

~~3.2.1 Cfin and CNT Chemistries with Fuming Sulfuric Acid (FSA) and~~

~~Chlorosulfomc Acid (CSA)~~

~~3.2.1.1 Reaction of Can with Fuming Sulfuric Acid and Chlorosulfomc Acid~~

Miller and coworkers studied fullerene reactivity towards superacids by dissolving Ceo in FSA and CSA at room temperature.236'25' We were however interested in observing reactivity under more aggressive reaction conditions like boiling FSA and

CSA. To that end, separate mixtures of Ceo in FSA and CSA were refluxed for ten hours under a nitrogen atmosphere. In the case of the reaction of C6o and FSA, the boiling mixture (b.p. of CSA =142 °C), turned green immediately (similar to the observation in ref. 256). Within half an hour of refluxing, it first turned to brick red then to red, and finally to a dark orange colored mixture. After cooling, the reaction mixture was slowly quenched with ice cold water and a brick-red solid was recovered. The IR spectra (Figure

~~3.7) and the 13C NMR spectrum in DMSO-d6 showed similar features of polysultones of~~

~~C6o as described in earlier reports.256'25. Hence, it was concluded that the same chemistries that occur in FSA at room temperature also happen at elevated temperatures.~~

When C6o was refluxed with CSA (b.p. of CSA = 152 °C), the reaction mixture first turned to reddish brown, and finally to greenish brown. After ten hours of refluxing, the resulting mixture was carefully quenched with crushed ice. Most of the precipitated

149 solid redissolved in the acidic-aqueous media. Even after the addition of a considerable amount of water and subsequent centrifugation, only a very small quantity of yellow brown solid was recovered. The IR spectrum (Figure 3.7) of the recovered solid is different than that reported for chlorinated Ceo by the reaction of Ceo and CSA at room temperature,256 but a detailed analysis of IR stretching vibrations was not conducted.

~~i i ' I. i~~

*S0Q V/svertumbgrs (cm-1) figure 3 FT-1K Spectrum of PolySttlKmetgd CM, X. (a) (b)

~~V ^ * <^-"»' .*. / \ A r / As y~~

Wavenutnbet1 (cm 1} Rgureg. FT-IR Spectrum of Chlorinated Cm X (c) (d) Figure 3.7: IR spectra of (a) polysultonated C6o~2S 6 and (b) from the reaction by refluxing Ceo in FSA. The IR spectra of (c) the chlorinated C6o"25"6 and (d) the brown solid recovered from the reaction by refluxing Ceo in CSA. Figure (a) and (c) are reprinted with permission from [256]. Copyright 1994 MRS E-Proceedings.

~~150 3.2.1.2 Reaction of MWNTs with Fuming Sulfuric Acid and Chlorosulfomc Acid~~

Given the structural similarities between CNTs and C6o, especially at the end caps, and given that C6o shows high reactivity towards superacids, we were interested to explore the reactivity of CNTs towards select superacids. Several interesting reports of

SWNTs dissolved or dispersed in superacids exist (cf. Section 3.1.4). To the best of our knowledge, however, there are no reports of effective reaction or dissolution of MWNTs in superacids. Hence, we started to investigate the reactivity/dissolution properties of

~~MWNTs in FSA and CSA.~~

MWNTs were refluxed in both FSA and CSA for ten hours. The tubes were not soluble in either acid at room temperature, but were well suspended at reflux. In both cases, the tubes precipitated after cooling the reaction mixtures to room temperature and quenching with crushed ice. Black solids were filtered and washed with additional water.

There was no visual change to the MWNTs, except that the recovered black solids from the CSA reaction had a flake-like texture. TEM and AFM images of MWNTs treated with FSA showed no significant changes. However, in case of MWNTs reacted with

CSA, the TEM and AFM images showed evidence for reduced bundling and broken end caps. The TEM and AFM images of MWNTs before (a - c, g) and after (d - f, h) reaction with CSA are shown in Figure 3.8. Evidence for broken tips is clearly demonstrated in

~~Figure 3.8 (d) and (f) while the debundled nature of MWNTs is depicted in the AFM image shown in Figure 3.8 (h) as compared to the bundled pristine MWNTs in Figure~~

~~3.8 (g).~~

~~151 Figure 3.8: TEM images of (a - c) pristine MWNTs; (d - f) MWNTs reacted with CSA; and AFM images of (g) pristine MWNTs and (h) MWNTs reacted with CSA on graphite (courtesy Dr. Jun-Fu Liu).~~

~~3.2.1.3 Future Direction~~

~~From the above discussion, it is clear that both C6o and MWNTs react with CSA.~~

However, more analytical characterizations are needed. The Ceo adduct recovered from the reaction with CSA should be characterized by NMR and mass spectrometry to help elucidate its molecular structure. We found that MWNTs are reactive in boiling CSA but 152 unreactive in boiling FSA. Raman spectroscopy may prove useful to characterize

~~MWNTs after treatment with boiling CSA.~~

~~3.2.2 Self-Assembly of CNTs with Latex Nanoparticles~~

~~Polystyrene latex (PSL) particles can be self-assembled on a metal chip with a~~

~~Au/PMMA patterned surface using electrophoresis."72 Based on this result, our aim was to investigate whether there is any promising interaction between PSL nanoparticles and~~

CNTs. Depending upon the strength interaction between CNTs and latex particles, electrophoresis could be used to assemble CNT-latex composites on the pattered metal substrate, which would then be treated with organic solvent to dissolve the PSL leaving patterned CNTs. The detailed discussion of electrophoresis methods is beyond the scope of this thesis and readers are recommended to consult the literature.273'272

Evidence for the self-assembly of CNTs on polymeric latex particles and vice- versa already exists in the literature (cf Section 3.1.5). However, in this project we were interested in using an aqueous solution of carboxylic acid functionalized SWNTs provided by Nantero Inc., USA.2,4 For this purpose, we investigated the interactions between the nanotubes with three different PSL particles such as non-functionalized PSL, carboxylated PSL and amino terminated PSL.

~~The self-assembly of SWNT and PSL onto a solid substrate was first attempted using a 'drop-and-drying' method.275 A drop from the mixture of the solution of SWNTs~~

(provided by Nantero Inc., 0.05 mL) and one drop of latex solution was added onto a carbon substrate, and slowly dried overnight in a fume hood before imaging by SEM. 153 Initially, it became difficult to draw any conclusion due to the high concentration of latex particles used for all the samples. However, careful review of multiple images suggested that the amino terminated and carboxy terminated PSL appeared to have stronger interaction with the nanotubes than the non-functionalized PSL. This might be because of partial bond formation between amino (NH2) groups of latex and the carboxylic acid groups of acid treated SWNTs or perhaps due to H-bonding interactions between the PSL particles and the SWNTs. SEM images of the self-assembled SWNTs in various PSL particles on carbon substrates are shown in Figure 3.9. An interesting bridging effect of

~~SWNTs by attachment through two stacks of latex particles near any cleavage sites is shown in Figure 3.9 (b) and (c) and is probably due to either non-bonding (HCOO—H-~~

OOC) or bonding (-CO-NH-) interactions between COOH or NH2 groups of the functionalized PSL particles and COOH groups of SWNTs respectively. This bridging effect however is missing in the case of SWNTs assembled in bare PSL, consistent with the involvement of carboxy terminated SWNTs and amino or carboxylic acid functionalized PSL.

~~154 Figure 3.9: SEM Images of SWNTs (from Nantero Inc., USA) and (a) bare, (b) carboxylated and (c, d) amino terminated PSL composites on carbon substrates.~~

To understand the interaction between SWNTs and PSL particles better, we next attempted to build self-assembled monolayers of the SWNT-PSL composites on a carbon substrate. Both the solutions of SWNTs and latex particles were diluted. Besides the

'drop-and-drying' method, we also employed a 'dip-and-drying' technique where the self- assembly was attempted by dipping the carbon substrate into the latex-SWNT solution and then drying it slowly. In the first case, we were able to form self-assembled monolayers of the latex-SWNT composite, and in the later case, both multi and mono

~~155 layers were observed (Figure 3.10). For these experiments, we utilized amino terminated~~

~~PSL particles.~~

Figure 3.10: SEM images of self-assembled monolayers of SWNTs and amino terminated PSL composites on carbon substrates by (a and b) 'drop-and-dry' and (c and d) 'dip-and-dry' methods after diluting solution mixture of both SWNTs and PSL.

~~We also investigated substrate effects on the self-assembly of the SWNT-PSL composites. For these experiments, a dilute mixture of SWNTs and amino terminated~~

~~PSL was dropped on three substrates made of silica, mica and gold/aluminum respectively. The resulting self-assemblies of SWNT-PSL composites are shown in~~

~~Figure 3.11. The SEM images demonstrate that the self-assembly of the SWNT-PSL 156 composite is partially substrate dependent. On silica (Figure 3.11, a - c) and mica~~

~~(Figure 3.11, e - f) the arrangement and orientation of the self-assembled composites are more uniform as compared to that on the gold/aluminum substrate (Figure 3.11 (d)).~~

~~I:II SiO, il>> ICI~~

We are also aware of the fact that the purchased latex solutions (c.f. Experimental) with variable pH values might contain some impurities including surfactants, water soluble salts and polymers with low molecular weights. These can all affect the self- assembly of the SWNTs and PSL particles. Hence, we need to purify the latex solutions

~~157 for any further studies. Nevertheless, based on the above observations, we expect that the nano-composite made with functionalized SWNTs and amino terminated or carboxylated~~

~~PSL have high potential for self-assembly on select substrates. Furthermore, we needed to investigate an electrophoretic method to assemble both SWNTs and amino terminated~~

~~PSL particles on patterned metal substrates. Preliminarily, we self-assembled amino- terminated PSL on Au/PMMA patterned substrates with the help of our collaborators at~~

Northeastern University. The resulting SEM of electrophoretic self-assembly of amino- functionalized PSL (Figure 3.12, (a)) is not as clean as that for unfunctionalized PSL particles (Figure 3.12, (b)).

~~UpS*''~~

~~Figure 3.12: SEM images of electrophoretic self assembly of (a) amino functionalized PSL and (b) bare PSL. Experiments performed at Northeastern University.~~

However, the self-assembly of PSL particles via electrophoresis is known to be dependent on various conditions such as the (1) concentration, (2) conductivity, (3) pH value and (4) particle size of the samples, as well as the (5) time of electrophoresis and

~~158 (6) voltage applied for the experiment. Hence, similar experiments should be performed using a variety of conditions to maximize self-assembly behavior.~~

~~3.2.2.1 Summary and Conclusions~~

~~The self-assembly of carboxy functionalized SWNTs with bare and functionalized~~

PSL particles was studied. According to our preliminary SEM analysis, we predict that carboxylated SWNTs interact more strongly with amino and carboxy terminated PSL particles than with unfunctionalized PSL. To examine the corresponding nano-composites more carefully, we prepared self-assembled monolayers of the nanocomposites by controlling the initial concentration of the solution mixture containing SWNTs and PSL particles. In this respect, the 'drop-and-dry' method followed by a slow evaporation of the solvent seemed more effective than the 'dip-and-dry' method. According to our SEM analysis, the self-assembly of SWNTs and amino terminated PSL particles is modestly substrate dependent. However we are also aware of the fact that the purchased latex solutions (c.f. Experimental) with variable pH values might contain some impurities including surfactants, water soluble salts and polymers with low molecular weights.

These can all affect the self-assembly of the SWNTs and PSL particles. Hence, we need to purify the latex solutions for any further studies. For future work, electrophoresis conditions should be systematically varied in order to maximize self-assembly behavior onto patterned substrates.

~~159 EXPERIMENTAL~~

~~Analytical Instrumentation~~

~~XH NMR Spectra~~

~~:H NMR spectra were obtained on a Varian Mercury Plus 400 FT-NMR operating at~~

~~399.768 MHz or a Varian INOVA 500 FT-NMR operating at 499.763 MHz. All chemical shift (SH) values are reported in parts per million (ppm) relative to (CH3)4Si (TMS) unless otherwise noted.~~

~~13C NMR Spectra~~

~~13C NMR spectra were obtained on a Varian Mercury Plus 400 FT-NMR operating at~~

~~100.522 MHz or a Varian INOVA 500 FT-NMR operating at 125.666 MHz. All chemical shift (8c) values are reported in parts per million (ppm) relative to (CH3)4Si (TMS) unless otherwise noted.~~

~~Mass Spectrometry~~

~~Time-of-flight matrix assisted laser desorption ionization (MALDI-TOF-MS or LDI-~~

~~TOF-MS) mass spectrometry was performed on a Shimadzu Kratos Axima-CFR running in reflectron mode.~~

~~160 UV-Vis Spectroscopy and Kinetic Studies~~

UV-visible spectra were obtained on a Nikolet Evolution 300 spectrometer using 1 cm quartz cells. Dilute solutions (2.0 x 10-4 M) of pentacene derivatives were prepared using degassed spectroscopic grade dichloromethane. The cells were protected from light until each experiment began, at which point an initial spectrum was recorded. Each cell was then exposed to air by loosening the cap to allow for free exchange of air, while minimizing solvent evaporation. The cells were placed on a laboratory bench under conventional 32 W, SP35 fluorescent lighting (General Electric, 2850 lm). The solutions were repeatedly scanned at prescribed intervals until less than 5% of the starting acene remained.

~~UV-Vis-NIR Spectroscopy~~

UV-visible spectra were obtained on a Cary 500 UV/Vis/NIR Spectrophotometer covers the wavelength range of 3300 nm (near infrared or NIR) to 175 nm (ultraviolet or UV) using 1 cm quartz cells. Solutions of acene derivatives were prepared using concentrated sulfuric acid from J. T. Baker (ACS reagent grade). The cells were protected from moisture until each experiment was done using Teflon cap on.

~~Solid State FTIR Spectroscopy~~

~~Infrared spectra of [60] fullerene treated with super acids were acquired using a Thermo~~

~~Scientific Smart Orbit with diamond ATR accessory.~~

~~161 TGA~~

~~Thermo gravimetric analysis was obtained using a Thermo Gravimetric Analyzer (TGA),~~

~~TGA Q5000 V3.6 Build 253. Samples weighing between 5 to 15 mg were heated from 0 to 500 °C using either Ramp or Hi-Res-Dynamic mode.~~

~~Cyclic Voltammetry~~

~~Cyclic voltammetry (CV) studies of each pentacene derivative were performed using a~~

~~BAS-100B electrochemical analyzer in a three-electrode single-compartment cell with a~~

~~Pt working electrode, Ag/AgCl reference electrode, and a Pt wire as auxiliary electrode.~~

~~Tetrabutylammonium hexafluorophosphate, TBAPF6, was used as supporting electrolyte~~

~~(0.1 M), and HPLC grade dichloromethane was used as solvent (no further purification).~~

A scan rate of 100 mV/s was typically employed. The concentration of pentacene derivatives was typically 0.5 mM. The Pt working electrode required cleaning between samples, especially before and after characterization of S containing 1 and 2. HOMO and

~~LUMO energies and electrochemical HOMO-LUMO gaps were determined from the onsets of the first oxidation and the first reduction waves.~~

~~Chromatography~~

~~Sand was obtained from Fisher Scientific Co.~~

~~Silica Gel (230-400 mesh) was obtained from Natland International Co.~~

~~Thin Layer Chromatography Plates were obtained from Fisher Scientific Co.~~

~~162 Solvents~~

Note: All solvents were used without further purification unless otherwise noted. Solvent drying was carried out for tetrahydro furan, toluene, methylene chloride, ethyl ether and dimethyl formamide as needed by distillation from sodium metal (THF, toluene) from molecular sieves or by passing through a silica column in a dry-solvent delivery system.

~~Acetic Acid (CH3C02H) was obtained from VWR Chemical Co.~~

~~Acetic Anhydride ((CH3CO)20) was obtained from Fisher Scientific Co.~~

~~Acetone (reagent grade) was obtained from Pharmco.~~

~~Benzene (C6H6) was obtained from EM Science.~~

~~Carbon Disulfide (CS2) was obtained from EM Science.~~

~~Carbon Tetrachloride (CCI4) was obtained from Aldrich Chemical Co.~~

~~Chloroform (CHCI3) was obtained from Fisher Scientific Co.~~

~~Deuterated NMR solvents were obtained from Cambridge Isotope Laboratories.~~

~~1,2-Dichlorobenzene (ODCB) was obtained from Aldrich Chemical Co.~~

~~Dichloromethane (CH2CI2) was obtained from Fisher Scientific Co.~~

~~Diethyl Ether ((CH3CH2)0) was obtained from Pharmco.~~

~~A^./V-Dimethylformamide (HCON(CH3)2) was obtained from Fisher Scientific Co.~~

~~Dimethylsulfoxide (DMSO) (anhydrous) was obtained from Alfa Aesar Chemical Co.~~

~~1,4-Dioxane ((CH2CH2)202) was obtained from Aldrich Chemical Co.~~

~~Ethanol (anhydrous) was obtained from Pharmco.~~

~~Ethanol (95%>) was obtained from Pharmco.~~

~~163 Ethyl Acetate (CH3CO2CH2CH3) was obtained from Fisher Scientific Co.~~

~~Hexanes were obtained from Fisher Scientific Co.~~

~~Methanol (CH3OH) was obtained from Pharmco.~~

~~Tetrahydro furan (THF) was obtained from Fisher Scientific Co.~~

~~Toluene (PhCH3) was obtained from Fisher Scientific Co.~~

~~Reagents~~

~~Note: All reagents were used without further purification unless otherwise noted.~~

~~Aluminum foil (Al°) was obtained from Reynolds.~~

~~Aluminum trichloride (AICI3) was obtained from Aldrich Chemical Co.~~

~~1 -amino-2.3-dimethylbenzene (C8HUN) was obtained from Acros Organics Co.~~

~~Ammonium chloride (NH4CI) was obtained from Fisher Scientific Co.~~

~~Anthracene (C14H10) was obtained from Aldrich Chemical Co.~~

~~Antimony pentachloride (SbCls) was obtained from Alfa Aesar Chemical Co.~~

~~Azobisisobutyronitrile (AIBN) was obtained from Aldrich Chemical Co.~~

~~1,4-Benzenediamine (CeHg^) was obtained from Aldrich Chemical Co.~~

~~1,4-Benzoquinone (C6H4O2) was obtained from Acros Organics Co.~~

~~Benzoyl peroxide (BPO) was obtained from Aldrich Chemical Co.~~

~~Benzyl bromide (CeH5CH2Br) was obtained from Aldrich Chemical Co.~~

~~Benzylthiol (CyHgS) was obtained from Alfa Aesar Chemical Co.~~

~~3,4-bis(ethoxycarbonyl)furan (Cio H12 O5) was obtained from Aldrich Chemical Co.~~

~~Borane THF Complex (BH3:THF) was obtained from Acros Organics Co.~~

~~164 Boric Acid (H3BO3) was obtained from Fisher Scientific Co.~~

~~Bromine (Br2) was obtained from Acros Organics Co.~~

TV-Bromosuccinimide (NBS) was obtained from Aldrich Chemical Co. n-Butanol (C4H10O) was obtained from Fisher Scientific Co. p-fert-Butylbromobenzene (C6HsBrC4H9) was obtained from Alfa Aesar Chemical Co.

~~4-fe^-butylthiophenol (C10H14S) was obtained from TCI America Co.~~

~~Calcium chloride (CaCl2) was obtained from Fisher Scientific Co.~~

~~Catechol (C6H602) was obtained from Aldrich Chemical Co.~~

~~Cesium carbonate (CS2CO3) was obtained from Alfa Aesar Chemical Co.~~

~~Chloranil (C^CUO?) was obtained from Aldrich Chemical Co.~~

~~Chlorosulfuric acid (HSO3CI) was obtained from Aldrich Chemical Co.~~

~~Copper(I) Bromide (CuBr) was obtained from Acros Organics Co.~~

~~Copper(I) Iodide (Cul) was obtained from Alfa Aesar Chemical Co.~~

~~18-Crown-6 (C12H24O6) was obtained from Aldrich Chemical Co.~~

~~1,4-Cyclohexanedione (CeHg02) was obtained from Alfa Aesar Chemical Co.~~

~~1,2-Di(bromomethyl)benzene (CgHgB^) was obtained from Aldrich Chemical Co.~~

~~2.3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) was from Aldrich Chemical Co.~~

~~4,5-dichlorophthalic acid (C8H4CI2O4 ) was obtained from TCI America Co.~~

~~1,4-Dihvdro-1,4-epoxynaphthalene (CioHgO) was obtained from Aldrich Chemical Co. p'-diaminobiphenyl (p.p'-bianiline/benzidine) (C12H12N2) was obtained from Fluka~~

~~(Sigma-Aldrich Co.)~~

~~Diisobutylaluminum hydride (DIBAL-H) was obtained from Aldrich Chemical Co.~~

~~165 Dimethylacetylene dicarboxylate (DMAD) was obtained from Aldrich Chemical Co.~~

~~Diphenyl disulfide (C12H10S2) was obtained from Aldrich Chemical Co.~~

~~1,3-Diphenylisobenzofuran (C20H14O) was obtained from Aldrich Chemical Co.~~

~~1-Dodecylthiol (Ci?H?fiS) was obtained from Alfa Aesar Chemical Co.~~

~~[60]Fullerene (C60) was obtained from MER Chemical Co.~~

~~Hydriodic Acid (HI) was obtained from Aldrich Chemical Co.~~

~~Hydrobromic Acid (HBr) was obtained from Alfa Aesar Chemical Co.~~

~~Hydrochloric Acid (HCl) was obtained from EM Science.~~

~~Hydroquinone (C6H6O2) was obtained from Fisher Scientific Co.~~

~~Iodine (I2) was obtained from Aldrich Chemical Co.~~

~~Lithium aluminum hydride (LiAlH4) (LAH) was obtained from Aldrich Chemical Co.~~

~~Magnesium sulfate (MgS04) was obtained from Fisher Scientific Co.~~

~~Maleic Anhydride (C4H2O3) was obtained from Alfa Aesar Chemical Co.~~

~~Mercury (II) chloride (HgCb) was obtained from Fisher Scientific Co.~~

~~Ar-Methyl-2-pyrrolidone (NMP) (C5H9NO) was obtained from Aldrich Chemical Co.~~

~~1,4-Naphthoquinone (CioH602) was obtained from Aldrich Chemical Co.~~

~~Nitric Acid (HNO3) was obtained from EM Science.~~

~~Palladium on activated carbon (10%> Pd/C) was obtained from Aldrich Chemical Co.~~

~~Phenyllithium (CeHsLi) was obtained from Aldrich Chemical Co.~~

~~Phenylmagnesium bromide (C6H5MgBr) was obtained from Aldrich Chemical Co.~~

~~Phthalic anhydride (C8H4O3) was obtained from Aldrich Chemical Co. o-Phthalaldehvde (C8H602) was obtained from Aldrich Chemical Co.~~

~~166 Potassium borohydride (KBH4) was obtained from Aldrich Chemical Co.~~

~~Potassium carbonate (K2CO3) was obtained from Fisher Scientific Co.~~

~~Potassium hydroxide (KOH) was obtained from EM Science.~~

~~Potassium iodide (KI) was obtained from Acros Organics Co.~~

~~Sodium (Na°) was obtained from Aldrich Chemical Co.~~

~~Sodium bicarbonate (NaHC03) was obtained from Fisher Scientific Co.~~

~~Sodium bisulfite (NaHSOs) was obtained from EM Science.~~

~~Sodium bisulfate (NaHS04) was obtained from J.T. Baker Chemical Co.~~

~~Sodium borohydride (NaBH4) was obtained from Aldrich Chemical Co.~~

~~Sodium carbonate (Na2C03) was obtained from Fisher Scientific Co.~~

~~Sodium chloride (NaCl) was obtained from J.T. Baker Chemical Co.~~

~~Sodium dithionate (Na2S204) was obtained from Acros Organics Co.~~

~~Sodium hydride (NaH) was obtained from Aldrich Chemical Co.~~

~~Sodium hydroxide (NaOH) was obtained from EM Science.~~

~~Sodium Iodide (Nal) was obtained from Acros Organics Co.~~

~~Sodium Nitrite (NaN02) was obtained from Aldrich Chemical Co.~~

~~Sodium thiosulfate (NaS203) was obtained from J.T. Baker Chemical Co.~~

~~Stannous chloride (SnCL.) was obtained from Alfa Aesar Chemical Co.~~

~~Sulfuric Acid (H2SO4) was obtained from J. T. Baker, ACS reagent grade~~

~~1,2,4,5-Tetrabromobenzene (Ce^B^) was obtained from Aldrich Chemical Co.~~

~~Tetrabutylammonium bromide (TBAB) was obtained from Aldrich Chemical Co.~~

~~Tetrabutylammonium fluoride (TBAF) was obtained from Aldrich Chemical Co.~~

~~167 1,2,4,5-Tetramethylbenzene (C10H14) was obtained from Alfa Aesar Chemical Co.~~

~~2,3,5,6-tetramethvl-1,4-benzenediamine (CioHi6N2) was obtained from Aldrich Chemical~~

~~Co.~~

~~2,3,5,6-Tetramethyl-1,4-benzenediamine (C10H12N2O4) was obtained from Aldrich~~

~~Chemical Co.~~

~~Thioacetic acid (C2H4OS) was obtained from Aldrich Chemical Co.~~

~~Thionyl chloride (SOCI2) was obtained from Aldrich Chemical Co.~~

~~3-Thiopropanoic acid (C3H602S) was obtained from TCI America Co.~~

~~Tin (II) chloride (SnCL.) was obtained from Aldrich Chemical Co.~~

~~Titanium (IV) chloride (TiCU) was obtained from Acros Organics Co.~~

~~Trifluoromethanesulfonic anhydride (Tf20) was obtained from Acros Organics Co.~~

~~Triethylamine (C^HisN) was obtained from Aldrich Chemical Co.~~

~~Trimethylsilyl iodide (TMSI) was obtained from Alfa Aesar Chemical Co. p-Toluenesulfonic acid (CH3C6H4SO3H) was obtained from Aldrich Chemical Co.~~

~~Zinc bromide (ZnBr2) was obtained from Acros Organics Co.~~

~~Zinc iodide (ZnL.) was obtained from Acros Organics Co.~~

~~168 Syntheses~~

~~Note: All routine solvent evaporations were conducted on a standard rotary evaporator using vacuum pump pressure unless otherwise noted.~~

~~Chapter 1: Syntheses~~

6,13-Pentacenequinone (23): 10%> aqueous NaOH (5.96g, 149 mmol) solution was slowly added to the solution of o-phthalaldehyde (lOg, 74 mmol) and 1,4- cyclohexanedione (4.18, 37.3 mmol) in 460 mL Ethanol. The solution then first turned yellow to golden brown, and then dark brown, and finally a yellow solid precipitated out of the solution. After stirring the reaction mixture overnight, the crude reaction mixture was filtered and washed with ethanol, water, then with methanol using a glass fritted funnel until the washing was colorless. The residue was dried under vacuum to obtain

~~! 11.02g (95% yield) bright yellow solid of 23. H NMR (500 MHz, CDC13) 8 (ppm): 8.96~~

~~(s, 4H), 8.14 (m, 4H), 7.72 (m, 4H); 13C NMR (100 MHz, DMSO-d6): 8 (ppm): 183.21,~~

~~135.45, 130.78, 130.31, 129.99, 129.67; LDI-MS mlz: [M+ + O], 324, [M++l] 309, [M+]~~

~~308.~~

6,13-Dihydroxy-6,13-dihydropentacene (24): To a 1000 mL round bottom flask containing a suspension of 23 (5g, 16.2 mmol) in 600 mL THF and 20 mL water, kept in an ice bath, NaBH4 (12.3g, 324.4 mmol) was slowly added. The reaction mixture was heated to 50 °C until everything was in a solution phase. After overnight stirring at room

169 temperature and evaporation of THF, water was added to the reaction mixture and filtered. The resulting solid residue was first washed with copious amount of water followed by a small amount of cold methanol and CHCI3. The white solid recovered, has only one isomer of 6,13-dihydroxy-6,13-dihydropentacene, 24. lH NMR (500 MHz,

~~DMSO-d6): 8 (ppm): 8.12 (s, 4H), 7.95 (m, 4H), 7.48 (m, 4H), 6.63 (s, 2H), 5.81 (s, 2H).~~

~~13C NMR (125.68 MHz, DMSO-d6): 8 (ppm): 138.19, 131.67, 127.47, 125.44, 120.91,~~

~~66.98. LDI-MS m/z: 312[M+], 295 [M+-OH], 278 [M+-2(OH)].~~

~~6,13-Pentacene-3,3'-bisthiopropanoic Acid (88) : To a flame dry Ar purged 75 mL glass bomb was added 89 (O.lg, 0.2 mmol) followed by IBX (0.1719g, 0.6 mmol) and 15 mL~~

DMSO capped with the Teflon cap. The mixture was heated to 60 °C by dipping the glass bomb into an oil bath and stirred for 17 hours in the dark. The resulting blue purple solution was then cooled and transferred to a beaker containing 100 mL water and filtered through a fritted funnel and washed with plenty of water followed by very small amount of acetone, copious amount of CH2CI2, CHCI3 and hexane. After drying using water suction in N2 atmosphere, the resulting blue solid was passed through a silica plug column using CH2CI2 as a loading solvent. The polarity was rapidly increased with addition of MeOH and the blue band was collected (100%> MeOH), evaporated and dried

~~1 to get 88 (6.6% yield). HNMR (400 MHz, CD3OD) 8 (ppm): 9.64 (s, 4H), 8.08 (m, 4H),~~

~~8.00 (m, 4H), 2.42 (t, 4H, J= 7.09). LDI-MS m/z: 486 [M+]; UV-Vis (MeOH) ?w at 611 nm, 564 nm and 526 nm.~~

170 6,13-Dihydro-6,13-Pentacene-3,3'-bisthiopropanoic Acid (89) : To a flame-dry N2 purged 250 mL round bottom flask anhydrous ZnL. (5.12g, 16 mmol), dihydroxypentacene 24 (2.5g, 8 mmol) and 200 mL dry CH2CI2 was added. To the mixture was added 1.22 mL (17.62 mmol) of 3-thiopropanoic acid. The resulting pink colored reaction mixture was then stirred for a day. There was a white colored solid precipitated out of the solution with progress of reaction. The resulting solid was then filtered and thoroughly washed with CH2CI2 followed by water. The white solid residue was dried to give 3.2g (81% yield) of dithiodihydropentacene 89. 1HNMR (400 MHz,

~~CD3OD) 8 7.96 (s, 4H), 7.89 (m, 4H), 7.49 (m, 4H), 5.59 (s, 2H), 2.97 (t, 4H, J= 7.28),~~

~~2.68 (t, 4H, J= 7.28); !HNMR (400 MHz, DMSO-d6) 8 (ppm): 12.32 (bs, 2H), 8.03 (s,~~

~~4H), 7.94 (m, 4H), 7.53 (m, 4H), 5.67 (s, 2H), 2.91 (t, 4H, J = 7.21), 2.67 (t, 4H, J =~~

~~7.21); 13C NMR (100 MHz, DMSO-d6): 8 (ppm): 173.17, 135.37, 132.04, 127.52,~~

~~127.18, 126.39, 46.74, 34.34, 28.29; LDI-MS m/z: 490.4 [M+2]~~

~~6,13-S,S'-Pentacene-bisthioacetate or 6,13-S,S'-pentacenethiol Acetate Pentacene~~

~~(91): To a flame-dry N2 purged 50 mL round bottom flask a mixture of 0.06g (0.139 mmol) trans-92 and 0.063g (0.278 mmol) DDQ was stirred in dry toluene (10 mL) at 100~~

°C for 48 hours under as Ar atmosphere in the dark. After cooling to RT, the resultant green reaction mixture was filtered and washed with CH2CI2. After evaporation of the filtrate, the dark green residue was passed through a short column of silica gel using a mixture of hexanes/CH2Ci2 (1:1) as an eluent to collect a blue band, which after solvent evaporation yielded a deep blue solid of pentacene 91 (8.7 mg, 4%> yield). :H NMR (500

~~171 MHz, CDCI3) 8 (ppm): 9.31 (s, 4H), 8.00 (m, 4H), 7.43 (m, 4H), 2.59 (s, 6H); LDI-MS~~

~~+ m/z: 426 [M ]; UV-Vis (CHC13) Tw at 621 nm, 573 nm and 533 nm.~~

6,13-Dihydro-6,13-S,S'-pentacenethiol acetate pentacene (92): To a flame-dry N2 purged 250 mL round bottom flask anhydrous Znl2 (2.04 g, 6.4 mmol), dihydroxypentacene 24 (l.OOg, 3.2 mmol) and 200 mL dry CH2CI2 was added. To the mixture was added 0.5 mL (7.03 mmol) of thioacetic acid. Within 10-15 minutes reaction mixture turned into a pinkish solution. The reaction was monitored by TLC and was completed within 2 hours. The reaction mixture was quenched with water and then the organic layer was extracted by CH2CI2 and washed with water followed by saturated aqueous NaHC03 solution, brine and dried over CaCi2. After evaporation of the solvents, the residue was purified by silica gel column chromatography using n-hexanes/CH2Ci2

~~(1:1) as eluent to give £rcm.y-6,13-dihydro-6,13-S,S'-pentacenetliiol acetate pentacene~~

~~r (92) as a pale yellow solid (1.26 g, 91% yield). H NMR (500 MHz, CDC13) 8 (ppm):~~

~~8.06 (s, 4H), 7.82 (m, 4H), 7.47 (m, 4H), 6.57 (s, 2H), 2.39 (s, 6H); 13C NMR (100 MHz,~~

~~CDCI3) 8 (ppm): 194.27, 135.17, 133.01, 127.86, 127.54, 126.61, 46.14, 30.49; LDI-MS m/z: 428 [M+].~~

6,13-Dithiohydroxy-6,13-dihydropentacene (93): To a N2 purged 50 mL round bottom flask was added 92 (0.05g, 1.2 mmol) followed by K2C03 (0.082g, 0.6 mmol) and 15 mL methanol and stirred for 15 minutes. To the resulting greenish white solution was added

~~NaBH4 (0.091g, 2.4 mmol) and stirred for overnight. The reaction mixture was quenched~~

~~172 with water followed by filtered through a fritted funnel and dried to recover white solid of two isomers (with the ration of 76 : 24 analyzed from NMR spectra) of 93 (0.036g,~~

~~90%> yield). The same reaction without any NaBH4 addition however yielded only one~~

~~: isomer. Major isomer: H NMR (500 MHz, CDC13) 8 (ppm): 7.97 (s, 4H), 7.84 (m, 4H),~~

~~7.48 (m, 4H), 5.85 (d, 2H, J= 6.37), 3.45 (d, 2H, J= 6.37); Minor isomer: !H NMR (500~~

~~MHz, CDC13) 8 (ppm): 8.09 (s, 4H), 7.84 (m, 4H), 7.48 (m, 4H), 5.90 (d, 2H, J= 3.9),~~

~~2.67 (d,2H,/= 3.9).~~

6,13-Bis(«-ethylthio)pentacene (96): To a flame dry Ar purged 75 mL glass bomb was added 99 (O.lg, 0.25 mmol) followed by K2C03 (0.35g, 2.5 mmol) and 10 mL dry benzene, and stirred under Ar atmosphere. After 10 minutes chloranil (0.123g, 0.5 mmol) was added to the reaction mixture followed by capped with the Teflon cap. The mixture was heated to 60 °C by dipping the glass bomb into an oil bath and stirred for 17 hours in the dark. After cooling down to the RT, the mixture was filtered and the filtrate was evaporated, and passed though a short column with pure hexane as an eluent isolate the blue band. After evaporation the resulting dark blue solid was collected to give 96

~~J (0.017g, 17% yield).). H NMR (500 MHz, CDC13) 8 (ppm): 9.73 (s, 4H), 8.07 (m, 4H),~~

~~7.41 (m, 4H), 3.07 (q, 4H, J= 7.32 Hz), 1.18 (t, 6H, J = 7.32 Hz) ; LDI-MS m/z: 398~~

~~+ [M ]; UV-Vis (CHC13) ^ at 616 nm, 569 nm and 529 nm.~~

~~6,13-Bis(«-dodecylthio)-6,13-dihydropentacene (98): To a flame-dry N2 purged 250 mL round bottom flask anhydrous Znl2 (2.04g, 6.4 mmol), dihydroxypentacene 24~~

~~173 (1 .OOg, 3.2 mmol) and 140 mL dry CH2CI2 was added. To the mixture was added 2 mL of~~

1-dodecylthiol (7.16 mmol). The reaction mixture was stirred for 2 hours and quenched with water and then the organic layer was extracted by CH2CI2 and washed with water followed by saturated aqueous NaHC03 solution, brine and dried over CaCl2. After evaporation of the solvents, the oily residue was purified by the silica gel column chromatography using «-hexanes as eluent to give white solids of trans (81%>) and cis

~~l (19%) isomers 98 (0.92 g, 42% yield). Trans isomer: R NMR (400 MHz, CDC13) 8~~

~~(ppm): 7.86 (s, 4H), 7.84 (m, 4H), 7.47 (m, 4H), 5.46 (s, 2H), 2.73 (t, 4H, J= 7.41 Hz),~~

~~1.73 (m, 4H), 1.43 (m, 4H), 1.26 (m, 32H), 0.88 (t, 6H, J = 6.63 Hz); 13C NMR (100~~

~~MHz, CDCI3) 8 (ppm): 135.41, 132.69, 127.71, 127.51, 126.26, 48.23, 33.99, 32.08,~~

~~29.84, 29.81, 29.79, 29.72, 29.52, 29.49, 29.41, 29.33, 22.84, 14.27. Cis isomer: *H NMR~~

~~(400 MHz, CDC13) 8 (ppm): 8.18 (s, 4H), 7.88 (m, 4H), 7.48 (m, 4H), 5.64 (s, 2H), 2.54~~

~~(t, 4H, J= 7.41 Hz), 1.66 (m, 4H), 1.38 (m, 4H), 1.24 (m, 32H), 0.87 (t, 6H, J= 6.63 Hz);~~

~~13 C NMR (100 MHz, CDC13) 8 (ppm): 135.22, 132.63, 127.82, 126.54, 126.23, 48.23,~~

~~32.07, 32.04, 29.81, 29.80, 29.75, 29.66, 29.64, 29.50, 29.41, 29.18, 22.85, 14.27.~~

~~6,13-Bis(ethylthio)-6,13-dihydropentacene (99): To a flame-dry N2 purged 250 mL round bottom flask anhydrous ZnBr2 (2.16g, 9.6 mmol), dihydroxypentacene 24 (1.5g,~~

4.8 mmol) and 150 mL dry CH2CI2 was added. To the mixture was added 2.8 mL of ethylthiol (38.4 mmol). The reaction mixture turned to a light yellow brown solution and completed within 30 minutes confirmed by TLC test. To the reaction mixture was added

~~100 mL water and the organic layer was extracted with CH2CI2 followed by washed with~~

~~174 water, saturated NaHC03 solution and brine. After evaporation of the solvent the resulting solid was passed through a short silica column with hexane as an eluent to yield~~

~~[ off white solid of single isomer of 99 (1.83 g, 95% yield). H NMR (500 MHz, CDC13) 8~~

~~(ppm): 7.87 (s, 4H), 7.84 (m, 4H), 7.47 (m, 4H), 5.48 (s, 2H), 2.78 (q, 4H, J= 1A Hz),~~

~~13 1.41 (t, 6H, J= 7.4 Hz); C NMR (100 MHz, CDC13): 8 (ppm): 135.24, 132.64, 127.7,~~

~~127.43, 126.27, 47.98, 27.94, 14.32; LDI-MS m/z: 402 [M+ + 2], 401 [M+ + 1].~~

Diethyl-4,5-dithiobenzylphthalate (102): NaH (1.98g, 82.42 mmol) was added to a flame dry N2 purged 500 mL three necked round bottom flask equipped with reflux condenser, containing 140 mL dry toluene and dipped into a ice bath. To the stirring suspension of NaH was slowly and carefully added a solution of 10 mL benzylthiol (85.3 mmol) with controlling the temperature below RT. After finishing the addition of thiol the reaction mixture was heated to 60 °C and diethyl 4,5-Dichlorophthalate (101, prepared following reported procedure of Polec,152 lOg, 34.34 mmol) was added in small portions

(lg). When addition of 101 was completed the temperature of the mixture was allowed to reach 80 °C and 6.9 mL NMP was added drop wise. Finally the resulting milky reaction mixture was heated to reflux for 20 hours. Then at RT it was transferred to a separating funnel, along with 140 mL EtOAc and 140 mL water. The extracted organic layer was dried over CaCl2, then filtered and the solvents were evaporated to yield a white solid of

~~l 102 (11.53g, 72% yield). R NMR (500 MHz, CDC13) 8 (ppm): 7.5 (s, 2H), 7.3 (m, 10H),~~

~~4.32 (q, 4H, J= 7.07 Hz), 4.17 (s, 4H), 1.34 (t, 6U, J = 7.07 Hz); 13C NMR (100 MHz,~~

~~CDCI3): 8 (ppm): 167.04, 140.68, 135.94, 129.73, 129.15, 128.76, 128.37,127.7, 61.77,~~

~~175 38.02, 14.2.~~

l,2-Hydroxymethyl-4,5-dithiobenzylbenzene (103): To a flame-dry N2 purged 250 mL round bottom flask was added 102 (6g, 12.86 mmol) followed by 70 mL dry THF and 40 mL borane (IM solution) and stirred under Ar atmosphere for 5 days monitored by TLC.

To the mixture water was added and the organic layer was extracted with EtOAc. The resulting organic layer was dried over CaCL., filtered, then evaporated followed by triturated with hexane to get rid of greenish oily part and collect a white solid of 103. lH

~~NMR (400 MHz, CDC13) 8 (ppm): 7.31 - 7.22 (m, 10H), 7.18 (s, 2H), 4.61 (bd, 4H, J =~~

~~13 4.87 Hz), 4.12 (s, 4H), 2.48 (bt, 2H, J= 5.07 Hz); C NMR (100 MHz, CDC13): 8 (ppm):~~

~~137.85, 137.26, 136.99, 131.13, 129.22, 128.64, 127.42, 63.70, 38.38.~~

~~4,5-Dithiobenzylphthaladehide (104): To a flame dry Ar purged 250 mL two-neck flask equipped with a thermometer and a dropping funnel was added a solution of 20 mL dry~~

~~CH2CI2 and oxalyl chloride (1.5 mL, 17.25 mmol). The stirred solution was cooled to -78~~

°C, and a solution of 2.58 mL DMSO and 5 mL CH2O2 was added drop wise. A solution of 103 (3 g, 7.84 mmol) in a mixture of CH2C12 (15 mL) and DMSO (1 mL) was also added to the flask drop wise. The reaction was allowed to stir for 0.5 h, and then triethylamine (21 mL, 0.14 mol) was slowly added at -78 °C. The resulting mixture was stirred for 10 minutes and then allowed to warm slowly to RT. Ice-cold water (50 mL) was added to the reaction mixture, and the aqueous layer was extracted with CH2CI2 (2 x

~~25 mL), followed by washing with saturated NaHC03 and then dried over CaCl2.~~

~~176 Evaporation of solvent gave crude 104, which was triturated using hexane, then filtered and the solid residue was washed with hot water and dried to yield pure 104 in 93% yield~~

~~J (2.76 g). H NMR (400 MHz, CDC13) 8 (ppm): 10.41 (s, 2H), 7.72 (s, 2H), 7.39 - 7.27~~

~~13 (m, 10H), 4.28 (s, 4H); C NMR (100 MHz, CDC13): 8 (ppm): 191.23, 144.01, 135.34,~~

~~133.1, 129.15, 128.91, 128.8, 127.97, 37.7~~

2,3,9,10-Tetrakis(benzylthio)-6,13-pentacenequinone (105): To a 250 mL round bottom flask equipped with reflux condenser was added a 104 (2g, 5.3 mmol), 1,4- cyclohexanedione (0.3, 2.7 mmol) and in 100 mL Ethanol. The mixture was heated to 60

°C to dissolve all the solutes. 10%» aqueous NaOH (0.42g, 10.5 mmol) solution was slowly added to the solution. The reaction mixture first turned yellow to brick brown and a brown solid precipitated out of the solution. After stirring and refluxing the reaction mixture for 24 hours, the crude reaction mixture was filtered and washed with methanol, then hexane, water, then with methanol again using a glass fritted funnel until the washing was colorless. The residue was dried under vacuum to obtain 1.5g (71 %> yield)

~~l yellow brown solid of 105. H NMR (400 MHz, CDC13) 8 (ppm): 8.67 (s, 4H), 7.80 (s,~~

~~4H), 7.44-7.30 (m, 20H), 4.31 (s, 8H)~~

2,3,9,10-Tetrakis(benzyltho)-6,13-dihydroxy-6,13-dihydropentacene (106): To a 100 mL round bottom flask containing a suspension of 105 (0.5g, 0.63 mmol) in 120 mL THF and 4 mL water, NaBH4 (0.14g, 3.76 mmol) was added. Within 3 hours of stirring the reaction mixture turned to a solution phase and it was stirred for overnight at room

177 temperature and monitored with TLC. After evaporation of THF, water was added to the reaction mixture and filtered. The resulting solid residue was first washed with of water dried to yield 0.47g pinkish grey solid of two isomers (81:19) of 106 (92.6% yield).

~~l Major isomer: R NMR (500 MHz, CDC13) 8 (ppm): 7.8 (s, 4H), 7.62 (s, 4H), 7.33 - 7.23~~

~~(m, 20H), 5.73 (d, 2H, J= 7.07 Hz), 4.21 (s, 8H), 3.25 (d, 2H, J= 6.83 Hz); 13C NMR~~

~~(125 MHz, CDCI3) 8 (ppm) 137.06, 136.80, 135.79, 131.63, 129.28, 128.76, 128.11,~~

~~! 127.56, 124.49, 71.39, 38.72. Minor isomer: H NMR (500 MHz, CDC13) 8 (ppm): 7.86~~

~~(s, 4H), 7.63 (s, 4H), 7.33 - 7.23 (m, 20H), 6.06 (d, 2H, J= 5.12 Hz), 4.21 (s, 8H), 2.27~~

~~(d, 2H,J=5.37Hz).~~

~~2,3,9,10-Tetrakis(benzyltho)-6,13-bis(4'-f-butylphenylthio)-6,13-dihydropentacene~~

(108): To a flame-dry Ar purged 50 mL round bottom flask anhydrous ZnBr2 (0.57g, 0.25 mmol), dihydroxypentacene 106 (O.lg, 0.13mmol) and 5 mL dry CH2Ci2 was added. To the mixture was added 0.5 mL of ^-butylthiophenol (0.28 mmol). The reaction mixture turned to a dark yellow brown solution and was stirred for overnight. To the reaction mixture was added 20 mL water and the organic layer was extracted with CH2CI2 followed by washed with water, saturated NaHC03 solution and brine. After evaporation of the solvent and triturated with hexane, the resulting solid was purified by a silica column with hexane and CH2CI2 mixture (1:1) as an eluent to yield lemon yellow colored two isomers (cis : trans = 80 : 20, from NMR data) of 108 (0.097 g, 70% yield). Cis

~~l isomer: H NMR (500 MHz, CDC13) 8 (ppm): 7.42 (s, 4H), 7.42 - 7.24 (m, 20H), 7.18 (s,~~

~~X 4H), 5.5 (s, 2H), 4.19 (s, 8H), 1.39 (s, 18H). Trans isomer: H NMR (500 MHz, CDC13) 8~~

~~178 (ppm): 7.79 (s, 4H), 7.55 (s, 4H), 7.31 - 7.19 (m, 20H), 5.83 (s, 2H), 4.17 (s, 8H), 1.27 (s,~~

~~18H).~~

~~9,10-Bis(phenylthio)anthracene (110): To a stirring solution of diphenyl disulfide (0.5g,~~

~~2.3 mmol) and anthracene (0.41g, 2.3 mmol) in CH2CI2 (25 mL) contained in a flame-dry~~

N2 purged 50 mL flask was added 0.3 mL SbCl5 (2.3 mmol). The dark resulting green solution was stirred for 10 minutes at RT and 10 mL water was added to it. The organic layer was extracted using CH2CI2 and washed thoroughly with water and then saturated solution of NaHC03 and brine. The solution was dried over CaCl2 and evaporated. There were five different spots corresponding to the recovered crude product (0.93g, >100% crude yield) detected by a TLC test. All different five products including 9,10-

~~Bis(phenylthio)anthracene (110), 9-(phenylthio)-anthracene (111), 9-chloro-10-~~

~~(phenylthio)anthracene (112), 9-chloroanthracene (113) and 9,10-dichloroanthracene~~

~~(114) were isolated using a preparative TLC plates run in hexane.~~

~~J 110: H NMR (400 MHz, CDC13) 8 (ppm): 8.95 (m, 4H), 7.57 (m, 4H), 7.12 (t, 4H, J =~~

~~7.21 Hz), 7.05 (t, 2H, J = 1.21 Hz), 6.96 (d, 2H, J = 1A Hz); 13C NMR (100 MHz,~~

~~CDCI3): 8 (ppm); 138.46, 135.35, 129.99, 129.16, 127.81, 127.48, 126.61, 125.35,~~

~~LDI-MS m/z: 394 [M+].~~

~~l Ill: H NMR (400 MHz, CDC13) 8 (ppm): 8.82 (d, 2H, J= 8.38 Hz), 8.61 (s, 2H), 8.06~~

~~(d, 2H, J= 7.6 Hz), 7.53 (m, 4H), 7.09 (t, 2H, J= 111 Hz), 7.01 (t, 1H, J= 7.21 Hz),~~

~~179 13 6.92 (d, 2H, J= 7.6 Hz); C NMR (125 MHz, CDC13): 8 (ppm) 138.87, 135.16, 132.13,~~

~~130.37, 129.08, 129.01, 127.41, 127.01, 126.36, 125.74, 125.36, 125.02; LDI-MS m/z:~~

~~286 [M+].~~

~~112: !H NMR (400 MHz, CDCI3) 8 (ppm): 8.9 (d, 2H, J= 8.97 Hz), 8.62 (d, 2H, J= 8.77~~

~~Hz), 7.65 (m, 4H), 7.1 (t, 2H, J= 7.4 Hz), 7.03 (t, 1H, J= 7.4 Hz), 6.91 (d, 2H, J= 7.99~~

~~13 Hz); C NMR (125 MHz, CDC13): 8 (ppm) 138.51, 135.43, 132.80, 129.46, 129.21, 127.65,~~

~~127.30, 126.39, 125.62, 125.50, 125.25; LDI-MS m/z: 320 [M+].~~

~~: 113: H NMR (400 MHz, CDC13) 8 (ppm): 8.51 (d, 2H, J= 8.77 Hz), 8.41 (s, 1H), 8.02~~

~~13 (d, 2H, J= 8.57 Hz), 7.61 (m, 2H), 7.52 (m, 2H); C NMR (100 MHz, CDC13): 8 (ppm);~~

~~132.08, 128.68, 127.26, 126.96, 126.16, 125.82, 125.37, 124.91.~~

~~13 114: *H NMR (400 MHz, CDC13) 8 (ppm): 8.56 (m, 4H), 7.65 (m, 4H); C NMR (100~~

~~MHz, CDCI3): 8 (ppm); 129.31, 127.25, 125.37; LDI-MS m/z: 247 [M+], 246 [M+- H].~~

~~l,4,8,12,15,19-Hexa(4'-r-butylphenylthio)-6,10,17,21-tetrahydroxy-6,10,17,21- tetrahydrononacene (116): To a suspension of 117 (0.01 g, 7.21 x 10"3 mmol) in wet~~

~~THF (THF : H2O = 3: 0.1) in a 50 mL round bottom flask purged with N2 was added~~

NaBH4 (0.003 g, 0.08 mmol). The reaction mixture was stirred at room temp for 3 hours until everything goes into a yellow fluorescent solution (monitored with TLC), and then quenched with H2O. The resulting mixture was filtered, washed with H20, and dried to

~~180 yield yellow solid (0.011 g, 90% crude yield). MALDI-MS m/z: 1531 [M+-H], 1513 [M+-~~

~~OH - H]; UV-Vis (CHC13) A,™ at 422 nm.~~

l,4,8,12,15,19-Hexa(4'-^-butylphenylthio)-6,10,17,21-nonacenequinone (117): To a solution of 118 (0.2 g, 0.37 mmol) and 119 (0.14 g, 0.18 mmol) in 70 mL DMF stirred in a flame dry Ar purged 150 mL glass bomb was added KI (0.4 g, 2.4 mmol). The resulting reddish suspension was heated and stirred at 110°C for 13 hours. After cooling to RT, the reaction mixture was filtered and washed with copious amount of water, and then acetone followed by hexane and cold CH2CI2 to yield a clean bright red solid of 117 (0.03 g, 10%

~~l yield). R NMR (400 MHz, CDC13) 8 (ppm): 10.15 (s, 4H), 9.5 (s, 4H), 7.37 (bs, 16H),~~

~~7.30 (bs, 4H), 7.18 (bs, 8H), 1.3 (s, 36H), 1.17 (s, 18H); MALDI-MS m/z: 1523.5 [M+].~~

~~6,9-Bis(4'-Mmtylphenylthio)-l,4-anthracenequinone (118): To a clear solution of 120~~

(0.8 g, 1.35 mmol) and 1,4-benzoquinone (0.39 g, 3.6 mmol) in 56 mL DMF stirred in a flame dry Ar purged 150 mL glass bomb was added KI (1.57 g, 9.46 mmol). The resulting reddish suspension was heated and stirred at 110°C for 17 hours. After cooling to RT, 100 mL water was added to the reaction mixture and the resulting brown solid was filtered washed with water and dried. The recovered solid was purified by column chromatography using silica. Mixture of hexane and CH2C12 (3:1) was used as eluent to collect a dark red band which after evaporation and drying yielded the red solid of 118

~~[ (0.44 g, 61% yield). H NMR (500 MHz, CDC13) 8 (ppm): 9.20 (s, 2H), 7.36 - 7.33 (m,~~

~~13 8H), 7.08 (s, 2H), 1.3 (s, 18H); C NMR (125 MHz, CDC13) 8 (ppm): 184.49, 151.69,~~

~~181 140.18, 137.17, 134.69, 132.4, 131.62, 129.89, 128.91, 126.89, 126.61, 34.82, 31.36.~~

~~LDI-MS m/z: 536 [M+].~~

l,4-Bis(4'-<-buty!phenylthio)-2,3,5,6-tetra(bromomethyl)benzene (119): To a flame- dry N2 purged 250 mL round bottom flask equipped with a refluxing condenser was added 121 (0.5g, 1.08 mmol) and it was dissolved in 30 mL dry CHCI3 by stirring. The solution was charged with NBS (1.15g, 6.46 mmol) and AIBN (0.18g, 1.09 mmol). The mixture was heated to reflux for 3 hour by irradiating with a 250 W tungsten lamp and the reaction was monitored by NMR for completion. After cooling to RT succinimide which precipitated as a colorless powder was filtered and washed with CH2CI2. After evaporation of solvent from the filtrate, the crude product was suspended in 25 mL

~~MeOH and stirred for 5 min to dissolve un-reacted NBS and by-products. The resulting suspension was filtered and the insoluble material was washed with MeOH to give white~~

~~: solid of 119 (0.82 g, 97% crude yield). H NMR (500 MHz, CDC13) 8 (ppm): 7.3 (m,~~

~~13 4H), 6.94 (d, 4H), 4.99 (bs, 8H), 1.28 (s, 18H). C NMR (125 MHz, CDC13) 8 (ppm):~~

~~149.72, 144.71, 137.15, 132.4, 126.73, 126.34, 34.62, 31.39, 29.08.~~

~~l,4-bis(4'-f-butyIphenylthio)-2,3di(bromomethyi)benzene (120): To a flame-dry N2 purged 250 mL round bottom flask equipped with a refluxing condenser was added 122~~

(lg, 2.30 mmol) and it was dissolved in 70 mL CC14 with stirring. Bromine (1.48g, 9.25 mmol) was then added to the solution and it was heated to reflux for 3 hour by irradiating with a 250 W tungsten lamp and the reaction was monitored by NMR. After completion

~~182 the solvent and bromine was evaporated and the residual yellow solid was thoroughly washed with water and then dried to yield clean product of 120 (1.05g, 77%). *H NMR~~

~~13 (500 MHz, CDC13) 8 (ppm): 7.32 (m, 4H), 6.94 (s,2H), 4.95 (s,4H), 1.30 (s, 18H). C~~

~~NMR (125 MHz, CDC13) 8 (ppm): 151.68, 137.62, 136.91, 132.58, 132.07, 130.19,~~

~~126.887,34.92,31.53,27.91.~~

l,4-Bis(4'-f-butylphenylthio)-2,3,5,6-tetramethylbenzene (121): To a flame-dry N2 purged 250 mL round bottom flask was added 123 (2g, 6.84 mmol), followed by cesium carbonate (8.9g, 27.32 mmol) and copper iodide (0.26g, 1.36 mmol). To the mixture was charged by 30 mL dimethylformamide followed by 2.64 mL 4-r-butylthiophenol (2.6 g,

15.64 mmol). The resulting suspension was heated to reflux for 2 days. Upon completion, the reaction mixture was cooled, filtered through a very small silica column (1 inch) and the filtrate was washed with water and saturated solution of Na2S207. The organic layer was extracted using EtOAc, washed with brine and then solvent was evaporated to give the crude product which was further purified by column chromatography using hexanes

~~J to yield white solid of 121 (2.85 g, 90% yield). H NMR (500 MHz, CDC13) 8 (ppm):~~

~~13 7.22 (m, 4H), 6.87 (m, 4H), 2.50 (s, 12H), 1.27 (s, 18H). C NMR (125 MHz, CDC13) 8~~

~~(ppm): 147.88, 140.50, 134.83, 133.35, 126.14, 125.69, 34.46, 31.46, 20.16.~~

~~l,4-Bis(4'-*-butylphenylthio)-2,3-dimethylbenzene (122): To a flame-dry N2 purged~~

~~250 mL round bottom flask was added 124 (2g, 7.57 mmol), followed by cesium carbonate (9.85g, 30.23 mmol) and copper iodide (0.29g, 1.53 mmol) and then 30 mL~~

183 dimethylformamide and 4-£-butylthiophenol (2.9 g, 17.44 mmol). The resulting suspension was heated to reflux for two days. Upon completion, the reaction mixture was cooled, filtered through a very small silica column (1 inch) and the filtrate was washed with water. The organic layer was extracted using EtOAc and washed with brine and then dried to give the crude product which was further purified by column chromatography using hexanes to yield colorless solid of 122 (2.89 g, 88% yield). JH NMR (500 MHz,

~~CDC13) 8 (ppm): 7.32 (m, 4H), 7.19 (m, 4H), 6.97 (s,12H), 2.42 (s,6H), 1.30 (s, 18H);~~

~~13 C NMR (125 MHz, CDC13) 8 (ppm): 150.16, 138.03, 134.58, 132.05, 130.69, 129.65,~~

~~126.41,34.62,31.42,17.85.~~

~~l,4-Dibromo-2,3,5,6-tetra(methyl)benzene (123): To a flame-dry N2 purged 250 mL round bottom flask equipped with a refluxing condenser and dropping funnel was added~~

1,2,4,5-tetramethylbenzene (10.0 g, 74.62 mmol) and 60 mL CH2C12 followed by I2 (0.4 g, 1.58 mmol). To this stirred solution Br2 (9.6 mL, 0.19 mol) in 40 mL CH2CI2 was added drop wise. After the addition was complete, the resulting solution was heated to boiling for 1.5 hours. Upon cooling, 20 mL aqueous solution of NaOH (5M) was added to quench excess bromine. The product was collected by filtration, washed with water and dried to yield white crystalline solid of 123 (18.6g, 85%). lB. NMR (400 MHz,

~~13 CDC13) 8 (ppm): 2.48 (s, 12H); C NMR (100 MHz, CDC13) 8 (ppm): 135.26, 128.36,~~

~~22.52.~~

184 l,2-Dibromo-2,3-dimethylbenzene (124): To a 100 mL two neck flask equipped with reflux condenser was added CuBr (1.61g, 11.22 mmol), 1.4 mL HBr (48%) and the mixture was started to reflux. Meanwhile, to a 100 mL Erlenmeyer flask equipped with thermometer and ice bath, was added 125 (4.01g, 20.04 mmol) and 5.7 mL HBr (48%).

To the stirring mixture, aqueous solution of NaNX>2 (1.379g, 20 mmol in 3.2 mL H2O) was slowly added so that temperature remained below 5 °C. After addition was finished the temperature of the reaction mixture was allowed to reach RT and then it was slowly added to the refluxing dark red brown solution of CuBr and HBr. After addition was complete the reaction mixture was refluxed for additional 3 hours and then allowed to cool to RT. The organic layer was extracted with CH2CI2, washed with water, saturated solution of NaHC03, brine and dried over CaCl2. After evaporation the solvent the residual brown oil was purified through a silica column using hexane as an eluent to yield light orange colored crystalline semi-solid of 124 (4g, 76%> yield). *H NMR (500 MHz,

~~13 CDC13) 8 (ppm): 7.23 (s, 2H), 2.43 (s, 6H); C NMR (125 MHz, CDC13): 8 (ppm);~~

~~137.85,130.94, 124.43,21.12.~~

~~l-Amino-4-bromo-2,3-dimethylbenzene (125): To a flame-dry N2 purged 250 mL round bottom flask was added 127 (6g, 24.78 mmol), 64 mL ethanol and 21 mL (12.1 M) HCl.~~

~~The heterogeneous reaction mixture was refluxed for two days and then cooled to RT.~~

After evaporation of the solvent 100 mL ice cold water was added and saturated NaOH solution was portion wise added to neutralize the acidity. The organic layer from the neutralized solution was extracted using EtOAc, washed with water, brine, dried over

~~185 : CaCl2 and evaporated to yield 4.82 g brown liquid of 125 (97.1% yield). H NMR (500~~

~~MHz, CDC13) 8 (ppm): 7.21 (d, 1H, J= 8.54 Hz), 6.44 (d, 1H, J= 8.54 Hz), 2.34 (s, 3H),~~

~~13 3.52 (bs, 1H), 2.39 (s, 3H), 2.13 (s, 3H); C NMR (125 MHz, CDC13): 8 (ppm); 143.85,~~

~~136.11, 129.97, 122.72, 114.45, 114.28,20.11, 14.21.~~

~~N-(4-bromo-2,3-dimethylphenyl)-acetamide (126): To a flame-dry N2 purged 250 mL round bottom flask was added 127 (lOg, 61.26 mmol), JV-bromosuccinimide (NBS,~~

11.45g, 64.33 mmol), 60 mL CHCI3 and the mixture was stirred and refluxed for 24 hours with hood lights on. After cooling it down to RT, the reaction mixture was filtered and washed with small amount of CHCI3. The filtrate was evaporated and the solid residue was thoroughly washed with copious amount of hot water and dried to give a clean 126

~~! as light brownish white cotton like solid (13.23g, 89.3%). H NMR (500 MHz, CDC13) 8~~

~~(ppm): 7.43 (bs, 1H), 7.32 (d, 1H, J= 8.54 Hz), 7.12 (d, 1H, J= 8.54 Hz), 2.34 (s, 3H),~~

~~13 2.14 (s, 3H), 2.12 (s, 3H); C NMR (125 MHz, CDC13): 8 (ppm); 169.05, 136.93, 134.59,~~

~~132.57, 130.08, 124.23, 122.89, 23.86, 20.37, 15.46.~~

N-(2,3-dimethylphenyl)-Acetamide (127): To a flame-dry N2 purged 50 mL round bottom flask was added 1 mL l-amino-2,3-dimethylbenzene (8.25 mmol) followed by 3 mL acetic anhydride and the reaction mixture solidified within 2 minutes. The system was then charged with saturated solution of sodium acetate, filtered and the solid was thoroughly washed with water and dried to yield light brown solid of 127 (1.07, 79.4% yield). *H NMR (500 MHz, CDC13) 8 (ppm): 7.4 (d, 1H, J= 7.81 Hz), 7.09 (t, 1H, J =

~~186 7.81 Hz), 7.02 (t, 1H, J= 7.81 Hz), 2.29 (s, 3H), 2.19 (s, 3H), 2.14 (s, 3H); UC NMR~~

~~(125 MHz, CDC13): 8 (ppm); 169.08,137.45,135.38, 130.47, 127.67, 125.72, 123.03,~~

~~23.79,20.56, 13.89.~~

~~l,4,8,ll-Tetra(4'-f-butylphenylthio)-6,13-pentacenequinone (128): To a solution of~~

118 (0.3 g, 0.56 mmol) and 120 (0.33 g, 0.56 mmol) in 70 mL DMF stirred in a flame dry Ar purged 150 mL glass bomb was added KI (0.62 g, 3.73 mmol). The resulting reddish suspension was heated and stirred at 110°C for 17 hours. After cooling to RT, the precipitated bright red solid was filtered and washed with copious amount of water, and then acetone and dried to yield a orange red solid of 128 (0.18 g, 35%> yield). XH NMR

~~(400 MHz, CDCI3) 8 (ppm): 9.51 (s, 4H), 7.37 (bs, 16H), 1.3 (s, 36H); 13C NMR (125~~

~~MHz, CDCI3) 8 (ppm): 182.49, 151.59,-137.06, 135.22, 133.19, 132.37, 131.71, 131.21,~~

~~130.19, 127.66, 126.87, 34.81, 31.39; LDI-MS m/z: 965 [M+].~~

~~l,4,8,12,15,19-Hexa(4'-^-butylphenylthio)-6,10,17,21-nonacene (129): To a flame dry~~

Ar purged 50 mL round bottom flask was added 116 (0.01 g, 0.007 mmol) followed by lml 1,4-dioxane and anhydrous SnCl2 (0.13 g, 0.68 mmol). To this yellow suspension was added 0.1 mL concentrated H2SO4 and the resulting mixture was stirred at room temperature for 0.5 hour in the dark. Water was added to the resulting reaction mixture, then filtered through fritted funnel and dried over Ar atmosphere to yield a grey colored solid (0.004g, 37%). MALDI-MS m/z: 1464 [M+]

187 General Procedure for synthesizing Acene Alcohols: To a suspension of acene mono quinone (1 mmol) in wet THF (THF : H2O = 30: 1) in a 50 mL round bottom flask purged with N2 was added NaBH4 (12 mmol). The reaction mixture was stirred at room temp for

~~3 hours until everything goes into a solution phase and no starting materials left~~

(monitored with TLC), and then quenched with H20. The resulting mixture was filtered, washed with H2O, and dried to yield acene alcohol. In case of acene diquinone all the reagents were used with increase the ratio to twice with respect to the quinone. All acene alcohols were characterized by NMR and/or by LDI-MS or MALDI-MS

~~6,17-Dihydroxy-6,17-dihydroheptacene (137) : :H NMR (500 MHz, DMSO-d6): 8~~

~~(ppm): (Major Isomer): 8.61 (s, 2H), 8.28 (s, 2H), 8.0 (bs, 4H), 7.5 (bs, 4H), 6.73 (d, 2H,~~

~~J= 6.35), 5.97 (s, 2H, J= 5.86). (Minor Isomer): 8.61 (s, 2H), 8.25 (s, 2H), 8.0 (bs, 4H),~~

~~7.5 (bs, 4H), 6.22 (bd, 2H, J = 4.39), 6.13 (bd, 2H). MALDI-MS m/z: All [M+], 395~~

~~[M+- OH], 378 [M+- 20H].~~

~~8,19-Dihydroxy-8,19-dihydrononacene (138): MALDI-MS m/z: 512 [M+], 495 [M+-~~

~~OH], 478 [M+- 20H].~~

~~5,7,12,14-Tetrahydroxy-5,7,12,14- tetrahydropentacene (141) : *H NMR (500 MHz,~~

~~DMSO-d6): 8 (ppm): (Major Isomer): 8.00 (d, 2H, J= 7.21), 7.63 (m, 4H), 7.26 (m, 4H),~~

~~6.27 (m, 4H), 5.34 (s, 4H). Minor Isomer: 7.88 (d, 2H,J= 7.21), 7.63 (m, 4H), 7.27 (m,~~

~~4H), 5.8 - 5.6 (m, 8H).~~

~~188 7,16-Bis(4'-/-butylphenyl)-5,9,14,18-tetrahydroxy-5,9,14,18-tetrahydroheptacene~~

~~(144): MALDI-MS m/z: 710 [M+], 693 [M+- OH], 676 [M+- 20H].~~

~~l,4,12,15-Tetra(4*-f-butylphenyl)-8,19-bis(4'-r-butylphenylthio)-6,10,17,21- tetrahydroxy-6,10,17,21-tetrahydrononacene (146): MALDI-MS m/z: 1291 [M+], 1274~~

~~[M+- OH], 12 [M+- 20H].~~

~~General Procedure for Acid Treatment on Acene Derivatives: All the acene derivatives mentioned to study their properties by treatment of concentrated H2SO4~~

(Section 1.2.4) are first dissolved in concentrated H2SO4 and the solution are used to study their spectral properties. In case of NMR analysis concentrated D2S04 was used as the solvent and TMS was used as the reference in a coaxial NMR tube.

~~J 6,13-Pentacenequinone (23): H NMR (500 MHz, D2S04) 8 (ppm): 8.66 (s, 4H), 7.59~~

~~13 (bm, 4H), 7.39 (bm, 4H); C NMR (125 MHz, D2S04): 8 (ppm): 185.35, 144.58, 138.46,~~

~~136.89, 135.45, 123.232.~~

~~! 6,13-Dihydroxy-6,13-dihydropentacene (24): H NMR (500 MHz, D2S04) 8 (ppm):~~

~~8.65 (s, 4H), 8.53 (bs, 2H), 7.53 (bm, 4H), 7.34 (bm, 4H).~~

~~189 Chapter 2: Syntheses~~

Bis [60] Fullerene Adduct of 2,3,9,10-Tetrakis(benzyloxymethyl)»6,13- diphenylpentacene (174): To N2 purged 100 mL round bottom flask quipped with a refluxing condenser was added C60 (0.54 g, 0.75 mmol) followed by 35 mL carbon disulfide and stirred vigorously to dissolve all the Ceo- To the purple solution was added

175 (0.14 g, 0.15 mmol) and the resulting dark purple blue mixture was stirred and heated to reflux for 17 hours in the dark. After cooling down to the room temperature and followed by evaporation of solvent, CH2CI2 was added to it and filtered using a fritted funnel and vacuum flirtation. The resulting brown filtrate was evaporated again followed by purified using a silica column and CH2CI2 as an eluent to yield brown solid of 174

~~l (0.07g, 20% isolated yield). U NMR (500 MHz, CDC13): 5 7.72 (m, 2H), 7.66 (s, 4H),~~

~~7.65 (m, 2H), 7.52 (m, 2H), 7.68 - 7.27 (m, 22H), 7.08 (m, 2H), 5.75 (s, 4H), 4.73 (s,~~

~~13 8H), 4.54 (s, 8H); C NMR (125 MHz, CDC13): 5 156.10, 155.54, 147.70, 146.69,~~

~~146.56, 146.38, 146.30, 145.96, 145.70, 145.55, 145.53, 145.47, 145.45, 145.40, 144.85,~~

~~144.75, 143.26, 142.75, 142.71, 142.62, 142.40, 142.18, 142.12, 141.82, 141.76, 141.63,~~

~~140.20, 139.89, 139.19, 138.22, 137.74, 137.03, 136, 99, 136.44, 135.88, 130.14, 129.98,~~

~~129.25, 129.02, 128.62, 128.33, 128.11, 127.89, 126.21, 72.72, 72.23, 69.65, 55.28; LDI-~~

~~+ MS m/z: 911 [M -C60].~~

2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenyIpentacene (175): To a N2 purged 50 mL round bottom flask was added 183 (0.24 g, 0.25 mmol) followed by 10 mL dioxane. 190 To the stirring yellow-brown solution was charged with excess SnCl2 (lg, 4.43 mmol) followed by 2 mL HCl in the dark under N2 atmosphere. The solution immediately turned to a dark purple mixture. After 30 minutes upon quenching with water, a blue-purple solid precipitated. The solid was filtered and washed with water and very small amount (1 mL) of cold methanol and dried in vacuo to yield blue solid of 175 (0.2lg, 98% crude

~~! yield). H NMR (500 MHz, CDC13): 5 8.29 (s, 4H), 7.76 (s, 4H), 7.71 (m, 4H), 7.67 (m,~~

~~2H), 7.62 (m, 4H), 7.33 (m, 16H), 7.29 (s, 4H) 4.70 (s, 8H), 4.55 (s, 8H); 13C NMR (125~~

~~MHz, CDCI3): 5 139.70, 138.33, 137.16, 133.99, 131.90, 130.50, 128.97, 128.97, 128.82,~~

~~128.56, 128.49, 128.04, 127.88, 127.81, 125.58, 72.55, 70.72; LDI-MS m/z: 911 [M+];~~

~~UV-vis (CHC13) ^(mn): 600, 555, 516, and in ODCB 604 nm, 558 nm and 518.~~

3,4-Bis(hydroxymethyl)furan (176): To a flame dry N2 purged 250 mL two neck round bottom flask equipped with a refluxing condenser was added 3,4- bis(ethoxycarbonyl)furan (5g, 23.56 mmol) followed by 16 mL dry diethyl ether and allowed to stir. The flux containing the mixture was placed in an ice bath to decrease the temperature up to 0 °C and lithium aluminum hydride or LAH (3.58g, 94.33 mmol) was carefully added in three portions followed by 40 mL additional dry ether. The resulting suspension was stirred and heated to reflux for 17 hours. After cooling it down to RT, the unreacted LAH was quenched with very slow addition of saturated solution of ammonium chloride. When there was no effervescence, to the mixture was carefully added 100 mL ethyl acetate. The solid was filtered and the filtrate was thoroughly washed with water and brine. The organic layer was dried over calcium chloride and evaporated 191 l to yield colorless oil of 176 (2.75g, 90% crude yield). H NMR (400 MHz, CDC13) 8

~~13 (ppm): 7.36 (s, 2H), 4.53 (bs, 4H), 3.48 (bs, 2H); C NMR (125 MHz, CDC13): 8 (ppm):~~

~~171.34,140.89, 124.38,54.90.~~

3,4-Bis(benzyIoxymethyl)furan (177): To a flame dry N2 purged 100 mL two neck round bottom flask was added 176 (2.67g, 20.85 mmol) followed by 35 mL DMF and the mixture was kept stirring. After cooling 0 °C by keeping it in an ice bath sodium hydride

~~(1.15g, 47.92 mmol) was carefully added in three portions and stirred. After 15 minutes~~

5.4 mL benzyl bromide (7.84g, 45.87 mmol) was added very slowly at 0 °C. After finishing the addition the resulting milky white-yellow suspension was stirred for 17 hours. The reaction mixture was slowly quenched with addition of 200 mL water and the organic layer was extracted with diethyl ether (50 mL x 3 times) and dried over CaCl2.

~~After filtering, the solvent was evaporated to yield orange oil. The oil was purified when it was passed through a silica column using hexane and EtOAc mixture (70 : 30) to yield~~

~~! of 177 (5.78g, 90% isolated yield). H NMR (400 MHz, CDC13) 8 (ppm): 7.40 (s, 2H),~~

~~13 7.36 - 7.27 (bm, 10H), 4.51 (s, 2H), 4.46 (s, 2H); C NMR (125 MHz, CDC13): 8 (ppm):~~

~~141.94, 138.32, 128.54, 127.97, 127.78, 121.95, 72.26, 62.72.~~

~~3,4-Bis(benzyloxymethyl)-7-oxabicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylic acid dimethyl ester (178): To a flame dry N2 purged 50 mL round bottom flask was added~~

~~177 (4.09g, 13.24 mmol) followed by 1.7 mL dimethylacetylene dicarboxylate (1.97g,~~

~~13.86). The mixture was heated to 110 °C and stirred for 3 hours. After cooling it down to~~

~~192 RT the mixture was passed through a silica column using a mixture of hexane and EtOAc~~

~~(70 : 30) as the eluent to yield orange colored oil of the enoxide 178 (5.43g, 90% isolated~~

~~X yield). R NMR (500 MHz, CDC13) 8 (ppm): 7.36 - 7.27 (m, 10H), 5.68 (s, 2H), 4.46 (m,~~

~~13 4H), 4.28 (m, 4H), 3.73 (s, 6H); C NMR (100 MHz, CDC13): 8 (ppm): 163.22, 152.79,~~

~~148.81, 137.89, 128.55, 127.89, 127.87, 86.97, 72.55, 64.18, 52.40.~~

~~l,2-Bis(methoxycarbonyl)-4,5-bis(benzyloxymethyl)benzene (179): To a N2 purged~~

~~flame dried 3-neck 500 mL round bottom flask equipped with refluxing condenser was~~

added 140 mL dry THF and the flask was stirred vigorously at 0 °C using an ice bath at the bottom of the flask. To the flask was carefully added 12 mL TiCU (108.79 mmol) and immediately turned yellow solution with dense fume inside the flask. To the resulting bright yellow suspension was carefully added LAH (1.28g, 33.73 mmol) in 3 portions

and the mixture turned green suspension with black solid floating. To it was added 17 mL triethyl amine (11.3 mmol) and the reaction mixture was heated to reflux for 30 - 45 minutes. After cooling it back to RT, the solution of 178 (2g, 4.44) in 45 mL dry THF was

~~added to the mixture and it was again heated to reflux (strongly restricted to below 100~~

~~°C) and stirred vigorously for 24 hours. After cooling it down to RT it was quenched with~~

~~200 mL water and organic layer was extracted with ether and EtOAc mixture. The~~

~~organic portion was also washed with saturated solution of NaHC03 and brine. After~~

~~evaporation a brown thick brown oil of 179 was recovered with 90% crude yield (1.73g).~~

~~(The crude oil could also be purified either using chromatography or by crystallization to~~

~~give off-white crystalline solid. However, crude compound was used to do next step most~~

~~193 ! of the time). H NMR (400 MHz, CDC13) 8 (ppm): 7.83 (s, 2H), 7.39 - 7.28 (m, 10H),~~

~~13 4.60 (s, 4H), 4.54 (s, 4H), 3.91 (s, 6H); C NMR (100 MHz, CDC13): 8 (ppm): 168.07,~~

~~139.90, 137.79, 131.29, 128.96, 128.65, 128.02, 72.88, 68.97, 52.77.~~

l,2-Bis(hydroxymethyl)-4,5-bis(benzyloxymethyl)benzene (180): To a flame dried N2 purged 500 mL two neck round bottom flask equipped with a refluxing condenser was added 179 (8.63g, 19.88 mmol) followed by 250 mL dry THF and allowed to stir. The flux containing the mixture was placed in an ice bath to decrease the temperature up to 0

°C and LAH (3.02g, 79.57 mmol) was carefully added in three portions followed by 100 mL additional dry ether. The resulting suspension was stirred and heated to reflux for 17 hours. After cooling it down to RT, the unreacted LAH was quenched with very slow addition of saturated solution of ammonium chloride. When there was no effervescence the, to the mixture was carefully added 100 mL ethyl acetate. The solid was filtered and the filtrate was thoroughly washed with water and brine. The organic layer was dried over calcium chloride and evaporated to yield oily residue. Upon triturating with hexane white

~~J solid of 180 was recovered (5.2g, 70% crude yield). H NMR (400 MHz, CDC13) 8~~

~~(ppm): 7.42 (s, 2H), 7.37 - 7.28 (bm, 10H), 4.74 (bs, 4H), 4.59 (s, 4H), 4.53 (s, 4H), 2.69~~

~~13 (bs, 2H); C NMR (125 MHz, CDC13): 8 (ppm): 139.12, 138.15, 136.69, 130.47, 128.60,~~

~~128.05, 127.92, 72.76, 69.48, 64.01.~~

~~4,5-Bis(benzyloxymethyl)-l,2-benzenedicarboxaldehyde (181): To a flame dried N2 purged 100 mL two-neck flask equipped with a thermometer and a dropping funnel was~~

194 added a solution of 15 mL dry CH2CI2 and oxalyl chloride (1.2 mL, 13.97 mmol). The stirred solution was cooled to -78 °C, and a solution of 2 mL DMSO and 4 mL CH2CI2 was added drop wise. A solution of 180 (2.3 g, 6.07 mmol) in a mixture of CH2CI2 (12 mL) and DMSO (0.7 mL) was then added to the flask drop wise. The reaction was allowed to stir for 0.5 h at -78 °C, and then triethylamine (15 mL, 0.1 mol) was slowly added. The resulting mixture was stirred for 10 minutes and then allowed to warm slowly to RT. Ice-cold water (45 mL) was added to the reaction mixture, and the aqueous layer was extracted with CH2CI2 (2 x 20 mL), followed by washing with much diluted acidic water followed by saturated solution of NaHC03 and then dried over CaCL:. Evaporation of solvent gave crude 181, which was triturated using hexane, then filtered and the solid residue was again dissolved in CHCI3 and passed through very short silica column (0.5 inch) using CH2CI2 solvent. Upon evaporation and drying a golden yellow orange solid

~~X of pure 181 (2.14 g, 87% isolated yield) was recovered. H NMR (400 MHz, CDC13) 8~~

~~(ppm): 10.54 (s, 2H), 8.08 (s, 2H), 7.41 - 7.29 (m, 10H), 4.65 (s, 4H), 4.59 (s, 4H); 13C~~

~~NMR (125 MHz, CDC13): 8 (ppm): 192.29, 142.64, 137.50, 135.59, 130.90, 128.68,~~

~~128.14, 127.99,73.18,68.74.~~

2,3,9,10-Tetrakis(benzyIoxymethyl)-6,13-pentacenequinone (182): To a 500 mL round bottom flask equipped with reflux condenser was added a 181 (4.88g, 13.03 mmol), 1,4- cyclohexanedione (0.73, 6.5 mmol) and in 200 mL Ethanol. The mixture was stirred vigorously to make a homogeneous solution. 5%> aqueous KOH (1.45g, 25.6 mmol) solution was slowly added to the solution. The reaction mixture first turned yellow then

~~195 brown, then golden brown finally yellow brown solid precipitated out of the solution.~~

After stirring and refluxing the reaction mixture for 2.5 hours, it was kept stirring for additional 8 hours at 60 °C. After cooling the crude reaction mixture was filtered and washed with ethanol, then hexane, water, then with ethanol again using a glass fritted funnel until the washing was colorless. The residue was dried under vacuum to obtain

~~3.37g (66%> crude yield) yellow brown solid of 182. After purification with the silica column with CH2CI2 bright yellow orange solid was recovered (3.1 g, 60%> isolated yield).~~

~~! H NMR (400 MHz, CDC13) 8 (ppm): 8.92 (s, 4H), 8.17 (s, 4H), 7.40 - 7.38 (m, 15H),~~

~~13 7.37 - 7.31 (m, 5H), 4.80 (s, 8H), 4.64 (s, 8H). C NMR (100 MHz, CDC13): 8 (ppm):~~

~~183.09, 138.58, 137.94, 134.84, 130.98, 129.56, 129.49, 128.69, 128.05, 128.04, 72.95,~~

~~69.84. MALDI-MS m/z: 790 [M+ +1], 789 [M+].~~

~~2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenyl-6,13-dihydro-pentacene-6,13-diol~~

~~(183): To an Ar purged flame dried 100 mL round bottom flask was added the solution of~~

182 (0.2 g, 0.25 mmol) in 40 mL dry THF. The light yellow solution was stirred and cooled to -78°C using dry ice/acetone bath. Upon cooling, phenyllithium (1.8 M, 5.41 mL, 9.74 mmol) was added drop wise over a 5 minutes period. The resulting dark green solution was allowed to warm to RT slowly and stirred overnight. The reaction mixture was quenched with saturated solution of NH4CI (50 mL). The resulting orange brown solution was then extracted with CH2C12 (100 mL) washed with water and dried over

~~CaCl2. The solvent was removed in vacuo until only -10 mL remained, at which point hexanes (100 mL) was added, resulting in the formation of a yellow white precipitate.~~

~~196 The diol was isolated by vacuum filtration (0.23 g, 95%). The resulting crude product was not subjected to further purification and used as such. *H NMR (500 MHz, CDCI3): 5~~

~~8.43 (s, 4H), 8.00 (s, 4H), 7.40 - 7.28 (m, 20H), 4.81 (s, 8H), 4.561 (s, 8H). 13C NMR~~

~~(125 MHz, CDCI3): 8 142.59, 139.75, 138.25, 134.89, 132.09, 128.61, 128.26, 128.12,~~

~~127.89, 127.79, 127.47, 127.02, 125.11, 76.58, 72.75, 70.33. LDI-MS m/z: 945 [M+], 927~~

~~[M+-OH], 911 [M+-2(OHVJ.~~

~~Bis[60]Fullerene Adduct of 2,3,9,10-tetraiodomethyl-6,13-diphenylpentacene (184):~~

To a flame dried N2 purged 5 mL round bottom flask was added a solution of 174 (0.027 g, 0.01 mmol) dry CDC13 (1 mL) followed by 0.1 mL trimethylsilyl iodide or TMSI (7.19 mmol) and capped well and stirred for 10 minutes. A brown solid precipitated out of the solution was then filtered. The resulting solid after thorough washing with CHCI3, acetone and methanol followed by drying under N2 atmosphere yielded dark brown solid

~~l of pure 184 (11.9g, 43.4% isolated yield). U NMR (400 MHz, CS2): 5 7.73 (m, 2H), 7.57~~

~~(m, 2H), 7.48 (m, 2H), 7.43 (s, 4H), 7.24 (m, 2H), 6.98 (m, 2H), 5.66 (s, 4H), 4.64 (s,~~

~~13 8H); C NMR (125 MHz, CDC13): 5 155.88, 155.42, 148.02, 146.98, 146.94, 146.71,~~

~~146.67, 146.14, 145.93, 145.88, 145.81, 145.72, 145.17, 145.13, 143.64, 143.48, 143.17,~~

~~143.06, 142.70, 142.55, 142.25, 142.07, 140.56, 140.33, 138.98, 137.81, 137.37, 137.32,~~

~~136.97, 130.62, 130.11, 129.99, 129.53, 128.97, 128.39, 72.77, 55.45, 2.81.~~

l,2-Di(iodomethyl)benzene (187): To N2 purged 100 mL round bottom flask quipped with a refluxing condenser was added 1,2-di(bromomethyl)benzene (lg, 3.78 mmol) 197 followed by sodium iodide (2.83g, 18.88 mmol) and 50 mL acetone. The mixture was stirred and heated to reflux for 17 hours. The resulting orange colored mixture was filtered and washed with acetone. The filtrate was washed with water, saturated solution of sodium bisulfate and brine. The organic layer was dried over CaCb, filtered and evaporated to yield yellow crystalline solid of 187. *H NMR (500 MHz, CDC13): 8 7.27

~~13 (m, 2H), 7.18 (s, 2H), 4.54 (s, 4H); C NMR (100 MHz, CDC13): 5 137.37, 130.81,~~

~~129.00,2.13.~~

6,ll-dihydro-dibenzo[b,f][l,4]dioxocin (190): To N2 purged 50 mL round bottom flask quipped with a refluxing condenser was added 187 (0.4g, 1.11 mmol) followed by catechol (0.12g, 1.11 mmol), potassium carbonate (1.54g, 11.1 mmol), 18-crown-6

(0.0lg, 0.04 mmol) and 10 mL o-dichlorobenzene (ODCB). The mixture was stirred and heated at 60 °C for 17 hours. The grey colored mixture was quenched with water and the organic layer was washed with a saturated solution of sodium thiosulfate and brine. The organic layer evaporated and the solid was triturated with ethanol. The white solid was

~~J filtered and dried to yield 190. H NMR (400 MHz, CDC13): 8 7.42 - 7.13 (m, 4H), 6.86~~

~~13 - 6.68 (m, 4H), 5.14 (bs, 4H); C NMR (100 MHz, CDC13): 8 148.92, 135.33, 128.66,~~

~~128.17, 121.73, 114.99,69.17.~~

1,4-Benzene diisoindoline (192): To the solution of 187 (0.36g, 1.0 mmol) and 5 mL o- dichlorobenzene (ODCB) stirred in a N2 purged 50 mL round bottom flask quipped with a refluxing condenser was added 1,4-benzenediamine (0.05g, 0.5 mmol), followed by 198 potassium carbonate (1.38g, 10 mmol) and 18-crown-6 (O.Olg, 0.04 mmol). The mixture was heated at 60 °C and stirred for 17 hours. A white colored solid precipitated out of the solution next day. To the mixture was added hexane filtered through a fritted funnel using vacuum filtration and the white solid was thoroughly washed with acetone followed by water followed by acetone then methanol and hexane. Finally it is also washed with very small amount of CHC13 and dried to yield white solid of 192 (0.08g, 41 %> crude yield).

~~LDI-MS m/z: 312 [M+].~~

~~2,3,5,6-Tetramethyl-l,4-benzene diisoindoline (193): Compound 193 was prepared using same procedure described for 192 except 2,3,5,6-tetramethyl-l,4-benzenediamine~~

~~(0.08g, 0.5 mmol) instead of 1,4-benzenediamine to yield white solid of 193 (0.09g, 60%> crude yield). LDI-MS m/z: 365 [M+].~~

[l,l'-Biphenyl]-4,4'-diisoindoline (194): Compound 194 was prepared using same procedure described for 192, p'-diaminobiphenyl (or p,p'-bianiline) (0.09g, 0.5 mmol) instead of 1,4-benzenediamine to yield white solid of 194 (0.18g, 93%> crude yield). LDI-

~~MS m/z: 388 [M+].~~

~~l,2,4,5-Tetrakis(bromomethyl)-3,6-dinitro-benzene (195): To a flame-dry N2 purged~~

250 mL round bottom flask equipped with a refluxing condenser was added 1,2,4,5- tetramethyl-3,6-dinitro-benzene (2.0g, 8.9 mmol) and it was dissolved in 35 mL dry CCI4 by stirring. The solution was charged with NBS (9.52g, 80.69 mmol) and AIBN (0.07g,

199 0.44 mmol). The mixture was heated to reflux for 53 hours by irradiating with a 250 W tungsten lamp and the reaction was monitored by NMR for reaction completion. After cooling to RT, the colorless powder of succinimide was filtered and washed with CH2C12.

~~After evaporation of solvent from the filtrate, the crude product was first washed with hot water and MeOH. The solid was then purified by recrystallization from CHC13 to give~~

~~! white solid of 195 (0.77 g, 16% crude yield). H NMR (500 MHz, CDC13) 8 (ppm): 4.48~~

~~13 (s, 8H); C NMR (125 MHz, CDC13) 8 (ppm): 152.09, 131.17, 20.19; LDI-MS m/z: 540~~

~~[M+],460[M+-Br].~~

~~2,3,9,10-Tetrakis(benzoyloxymethyl)-6,13-dihydroxy-6,13dihydropentacene (210):~~

~~The di-hydroxy pentacene 210 was prepared from 182 (0.5g, 0.63 mmol) following same procedure described previously for the dihydroxy compound 230 to obtain 0.47g pinkish~~

~~l white solid with 94% crude yield. Major isomer: K NMR (500 MHz, CDC13) 8 (ppm):~~

~~7.94 (s, 4H), 7.81 (s, 4H), 7.38 - 7.29 (m, 20H), 5.76 (d, 2H, J= 7.56 Hz), 4.77 (s, 8H),~~

~~l 4.59 (s, 8H), 3.47 (d, 2H, J = 7.56 Hz). Minor isomer: R NMR (500 MHz, CDC13) 8~~

~~(ppm): 7.99 (s, 4H), 7.84 (s, 4H), 7.38 - 7.29 (m, 20H), 6.12 (m, 2H), 4.77 (s, 8H), 4.58~~

~~(s, 8H), 2.48 (m, 2H). LDI-MS m/z: 775 [M+ - OH], 758 [M+ - 20H].~~

~~2,3,9,10-Tetrakis(benzoyloxymethyl)-6,13-dihydropentacene-3,3'-bisthiopropanoic acid (211): The dihydro pentacene derivative 211 was prepared from 210 (0.2g,~~

~~0.25mmol) following same procedure described for 143 to yield pinkish yellow solid of only one isomer of 211 (0.19g, 76% crude yield). XHNMR (400 MHz, DMSO-d6) 8~~

~~200 (ppm): 8.00 - 7.92 (m, 8H), 7.37 - 7.25 (m, 20H), 5.60 (s, 2H), 4.71 (s, 8H), 4.53 (s, 8H),~~

~~+ + 2.81 (bs, 4H), 2.22 (bs, 4H); LDI-MS m/z: 862 [M - SCH2CH2COOH], 757 [M -~~

~~2(SCH2CH2COOH)].~~

~~Computational Methods~~

All coordinates were first constructed and optimized by Spartan '04 using MMFF94 force-field on a Dell Optiplex GX280 (Intel Pentium 4 x86, 32-bit, 2.79 GHz, 3 GB memory). Further semi-empirical or DFT geometry optimizations and subsequent single- point energies of all resulting coordinates were refined using Gaussian '03 (Linux) on a

~~Dell PowerEdge 2970 Server running 6 Dell PowerEdge R610 nodes (Quad-Core AMD opteron x86, 64-bit, 2.8 GHz, 24 GB memory) via a Dell PowerConnect 5458 Network~~

~~Switch, each operating OpenSuSE 11.2, unless otherwise noted.~~

~~Table 2.4~~

All model structures were initially constructed using Wavefunction's Spartan '04 suite of programs (zero-point energies uncorrected). Next, all the unsubstituted as well as functionalized cyclacenes were optimized using B3LYP with a double-zeta valence

(DZV) basis set (6-31G*). Afterwards the SPE calculations for all cyclacenes were executed using an unrestricted broken-spin symmetry (UBS) wave function and the DFT method with triple-zeta valence (TZV; 6-311+G**) basis set.

~~201 Table 2.5~~

There were certain difficulties regarding the convergence of the optimization of the cyclacenes 203, 204, 205 and 208 using higher level DFT calculation in the beginning. Hence, those cyclacenes were first optimized using a lower level semi- empirical method (PM3) and then refined using DFT with a DZV basis set ((B3LYP/6-

~~31G*). Further UBS DFT method with TZV (UB3LYP/6-311+G**) was used to calculate~~

~~SPE, HOMO, LUMO and (Table 2.5).~~

~~Chapter: 3~~

~~Morphological studies using Imaging Techniques~~

~~Transmission Electron Microscope (TEM) of Super Acid Treated Carbon Nanotubes~~

TEM samples were prepared by placing dispersions of carbon nanotubes after 30 seconds of low-power sonication on either holey carbon or holey silicon grids and then evaporating the solvent. The morphologies of SWNTs before and after super acids treatments were compared using a Zeiss/LEO 922 Omega Transmission Electron

~~Microscope (TEM) with accelerating voltages of 120 kV and 200 kV The system has magnification from 80X to 1,000,000X with a resolution line of 0.12nm.~~

~~Scanning Electron Microscopy of Latex- Carbon Nanotubes Composites~~

~~Three different latex particles were used to prepare the sample of latex- carbon nanotubes~~

~~202 composites for SEM imaging, such as polystyrene latex particles (from Duke Scientific~~

~~Corp.; particle size with 0.048 urn diameter, red fluorescing, 1%> solid), amino polystyrene latex particles (from Polysciences Inc.; particle size with 0.083 um diameter,~~

2.75%o solid), carboxy polystyrene latex particles (from Polysciences Inc.; particle size with 0.048 um diameter, 2.6%> solid). One drop of the latex solution was added to 0.05 mL single walled carbon nanotube solution obtained from Nantero Co. The mixture was allowed to sonicate in low power bath sonicator for two minutes. One drop of the sample were placed on to solid substrates (Polished carbon planchet (1/2" x 1/16", \polished) -

Ernest F. Fullam, Inc. Product # 17610) and evaporated slowly to dry. The SEM imaging was performed using Amray 3300FE field emission SEM with PGT Imix-PC microanalysis system provides three-dimensional visual interpretation and elemental analysis of a specimen surface. The electron optics allow a depth of focus nearly 300X that of the light microscope, as well as a magnification range from 15X to lOOkX at accelerating voltages from l-25kV.

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~~274Sivarajan, R.; Ruckes, T.; Sen, R.; Segal, B. M.; Ghenciu, E. G.; Ward, J. W.; (Nantero, Inc., USA). PCT Int. Appl. 2006,40.~~

~~275Duggal, R.; Hussain, F.; Pasquali, M.; Adv. Mater. 2006, 75, 29.~~

~~222 APPENDICES~~

~~Abbreviation~~

~~Spectra~~

~~223 ABBREVIATION~~

~~Ag20: Silver oxide~~

~~Alq3: Tris(8-hydroxyquinolinato)aluminium Aq: Aqueous Ar: Argon CASSCF: complete active space self-consistent field~~

~~(CH20)n: Paraformaldehide~~

~~CeF5H: Pentaflorobenzene CNT: Carbon nanotube CV: Cyclic Voltammetry~~

~~DFT: Density functional theory~~

DSC: Differential scanning calorimetry Eq.: Equivalent FET: Field effect transistors FTIR: Fourier transform infrared spectroscopy GIXD: Grazing incidence X-ray diffraction HOMO: Highest occupied molecular orbital HOPG: Highly ordered pyrolytic graphite IBX: o-idodoxybenzoic acid LUMO: Lowest unoccupied molecular orbital MALDI-MS: Matrix assisted Laser Desorption lonisation Mass Spectrometry MMFF: Molecular Mechanics Force Field MWNT: Multiwalled carbon nanotube LDI-MS: Laser Desorption lonisation Mass Spectrometry MO: Molecular orbital

~~224 NiO: nickel(II)oxide NiOx: off-stoichiometric NiO NH4PF6: Ammonium hexafluorophosphate NPB: AyV-bis(l-naphthyl)-AyV-diphenyl-1,1 -biphenyl-4,4-diamine~~

~~OLED: Organic light emitting diode~~

OSC: Organic solar cell OPV:Organic photovoltaic OTFT: Oraganic thin film transistor PCE: Power conversion efficiency (%) PMMA: poly(methyl methacrylate) PVP: poly-4-vinylphenol PQ: pentacene quinone Pd/C: Palladium on carbon Re: Rhenium RT: Room temperature SCLC: Space charge limited current STM: Scanning Tunneling Micrograph SWNT: Single walled carbon nanotube TGA: Thermogravimetric analysis

~~TPD:N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine TPP: triphenylmethyl perchlorate UV: Ultra violet VB: Valence-bond~~

~~225 6,13-Pentacenequinone (23) u Q U * CDC1, N ffl~~

~~O in CN~~

~~/"L~~

~~(Ht) 3UOUinb3U3DB;U3J-£X69 Mass Spectra~~

~~M lii &. W S«& O S3 O w Q~~

~~as \» J&* u» I *d as * rs m'\ ft S3 ft~~

~~= o s* '^^^SZT^*' -fiDL O w ' CD 53 ft~~

~~c*> o ) CD i O c_ 0) \ /)~~

~~CQ'~~

~~8 CO o \ ) oo CO CO \ /)~~

~~228 ™3sJ (j- x Z £ *• S 9 L 8 € OT _l I I I I I I I I I I I I I I I I 1 I I I I 1 I l_ J I I I I I I I I I I I I I I I 1 I I I I I I I 1 I I l_ NT-~~

~~™sa s'L »*s s'% o-6 s'€ eroi s*ox J I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I L S /»—"\ f \/*— 1~~

~~K % SJALI~~

o o fosza *

~~(£Z) 3uouinb3U3DB;u3j-£x69 6,13-Pentacenequinone (23)~~

* TMS | )#|iHWMWPKtf^^<^ "T I I I I I I I [ I I I I I T" 1 ' I ' ' ' ' I n—i—|—i—r 180 178 1£Q 150 Mff 135 128

~~Solvent: Cone. H20S,JWO4 2.5-~~

~~CD O c co 2.0- o a> .Q < 1.5- T3 CD (N .N "CO X = 628 nm £ 1.0- max~~

~~0.5-~~

~~0.0-~~

~~-1— -1 300 400 500 600 700 800 Wavelength (nm) L m NMR (500 MHz, CDC13) r ^ //~~

~~o, )—( o as~~

~~yj a O~~

~~t \ ) i ON~~

~~i g- a o ft~~

~~P-K &9 ft ft~~

~~o O • r =53F:~~

~~232 6,13-Dihydroxy-6,13-dihydropentacene (24)~~

~~i H20* *DMSO O HOv.H~~

~~N HO H rn CN o in~~

^—y JL „JL —1—i—i—i—i 1 1—i—i—i—|—i—i—i 1—|—i—i—i—i—]—i—i—i—i—]—i—i—i—i—|—i—i—i 1—|—i—i—i—i—[—i—i—i—i 1—i—r 937654323. ppan

~~a.oe 13C NMR (100 MHz, DMSO-d6)~~

~~mH o~~

~~M •~~

~~M O o~~

~~I H O HO e o~~

~~S3- - '~~

~~o ft~~

~~: : a ft ft * . j 4-^ GO o O~~

~~a -~~

~~234 6,13-Dihydroxy-6,13-dihydropentacene(24)~~

~~291 m¥tsaiu= 39913 mVJ Proftfes 1 -13? Ssnootti fit/ 20 -Bass** 80 Molecular Weight: 312.36 278.4 M+- OH = 296.36 JOOj M+-2 x OH = 278.35 C3 se~~

ats- cu IT) CO ft I 2 Outturn 273 rfV] PBSes i »3? Snt A> 2 CN 3114 1/3 t/5 60-J i 50-" 295.4 309 3 J / 1 2%4 310 3 314 6 I 305 4 201 313 4 3071 317 4 265 3 2943 -x / — *• ij- 'F I ' x 10 310 ill 312 30 3M 3SS 3» iff 3>« 31= 1 -I. 01 t sA »N&MW'„ i\ii.,.„.l Vj,« MS SO 280 2S£ 3ffl3 310 329 330 340 356 380 370 380 390 «0 Mass&harge m NMR (500 MHz, D2S04)

ON 6 a oI-*

~~O ft 13 ft ft yj ft - = o ;M; o~~

~~236 X HNMR (400 MHz, CD3OD)~~

~~ft S3 ft i o> I-* I a V3 £, &s 3 ft a~~

~~EC e o IS~~

~~00 00 B -~~

~~•5?~~

~~237 HOOC 3,3'-(Pentacene-6,13- diylbis(sulfanediyl))dipropanoic acid (88)~~

~~COOH 616 ra'4sun= 283493 mVJ Proffes 1-42S Sw»fe ft¥ 20 -Sssetane X Molecular Weight: 486.60 382.5~~

~~so + M - CH2CH2COOH = 413.53 ao 00 + m ft M - (2 x CH2COOH) = 398.58~~

~~30 34,1.4 397.4 20 -Ol*J;»J..i™r~~

~~1.0 3*6.2 486.5 3i7I ft 413.5 wir4^tJA 4^A^!v«>^^^ 340 3S6 380 370 430 410 420 _a*_ 44© 4S0 410 4S0 490 SCO UV-Vis Spectra Absorbance o o o o o o fO .b. m GO~~

~~239 3,3f-(6,13-Dihydropentacene-6,13-diyl)bis(sulfanediyl)dipropanoic acid (89) HOOC~~

~~Isolated product~~

~~i I i i i i 1 i i i i I i i i i I i i i i j i i i i 1 i i i i I i i i i I r O }.0D 2.SS 2.98 2.85 2.U 2.75 2.70 2.55 •sl-~~

~~^•^ —i—|—r—i—i—1—j—i—i—i—i—|—i—i—i—i—[—i—i—i—i—|—i—i—i—i—]—i—i—r 0^ 8.0 7.9 7-8 7,7 7.6 7,5~~

*MeOH *H20

JL. J ^j VuJUL ]J ll_ "I 1 1 1 1 1 1 1- -i—| 1 1—i 1—| 1—i 1—i 1 r- -1 1—i 1—i—| 1—i 1 1 1—i—i 1—i p S 7 6 5 4 3 2 10 3,3f-(6,13-Dihydropentacene-6,13-diyl)bis(sulfanediyl)dipropanoic acid (89) Isolated product HOOC DMSO S. i H O t/3

~~(N O o~~

~~Isolated product oi *DMSO HOOC~~

~~O o~~

~~WW i i i—i i i i in i—i—i—i—i—i—i—i—i—i—i' i i •( i 'i-i-i-i i i i «-.W...... , i i i i i i i i i i 3,3'-(6,13-Dihydropentacene-6,13-diyl)bis(sulfanediyl)dipropanoic acid (89)~~

NIB: 31 «nVfsu!iF t?4 ffi¥| Prunes 1-53 S«seft A- 20 -Basetoe 80 309 4 MM] 490 4 382 4 H00C 90- | 383 4 b »i "i 4!14 70- o »1 CN HOOC 39 4 !ZS 380 I 7 ®1 418 3 Molecular Weight: 488.62 504 4 4-J9: 1 i SI <90 400 410 43» 440 450 480 478 -SO 4

~~3824 490.4 383.4 "j ,Li 1. .. * i , i. 1 i ^ 340 380 380 4C» 420 440 «0 480 500 TGA~~

~~Weight |%) Os u>~~

~~S3-~~

~~\ // a o~~

~~\ // c/a S3~~

~~o- o X ft % //~~

~~00 CL % //~~

~~o- c o~~

~~>T3 > o~~

~~244 *H NMR (500 MHz, CDC13)~~

~~1"" ft~~

~~ft 1 as~~

~~•a 245 S,Sf-Pentacene-6,13-diyl diethanethioate (91)~~

~~%u *27 rrVfs«fr= 3>1S reV] Rrottes 1-25 Sn«* A¥ 20 -Basetwe ® 9 X CH =395 52 Molecular Weight: 426.55 30?-5 - H,CO = 395.52 *- -COCH = 383.51 +^ 3 4265 m - 2 x OCH3 = 370.53 m a~~

~~V^ \ UV-Vis (CHC13) lmax at 621 nm, 573 nm and 533 nm. 08- 0 07 +*- o 06 p. 05~~

~~o < 03^~~

~~01 oa H~~

~~01 350 400 450 550 B50 Wawelength(nm) 'H NMR (500 MHz, CDC1 ) w 3 o o Q f Tt~~

~~248 *H NMR (500 MHz, CDC13) U_~~

~~ST: C/5~~

~~o -a i o o « ft o ft S3 &9 ^ w *» ft 53 ft I ON til b *4 I a <^ a o • •-*• t. _ ft P ft~~

~~91 - o~~

~~ft o~~

~~s v.~~

~~249 13C NMR (100 MHz, CDCL)~~

~~m t/5 o ^ //~~

~~OS \ // GO GO o X~~

~~250 S,S'-6,13-Dihydropentacene-6,13-diyl diethanethioate (92)~~

~~•i o~~

~~OH I CN 428.2 1 50- I 322.1 «- 1 I SO- Molecular Weight: 428.57~~

20] 315.2| 352.0 414.2 »1 •"•»•"•"* » r-"" v*""w !»•••• 4*5 Wf^i» 310 1® 33§ 34S 353 3® 3?B mi 380 «0 410 4» 440 MasfcChaigie S,S'-6,13-Dihydropentacene-6,13-diyl diethanethioate (92)

~~120~~

~~238.3C*C 99.47% 108 —k.~~

~~< CN O m H CN SO- SB . 2B8.S2"C ^65.72%~~

~~SO'~~

~~\ \ \ 40 1QQ 150 200 250 300 350 400 Temperature f C) Univeraal V4.SA TA instruments w&<$ T f L I I I _1_J L__l_ _1 I I I 1_ _i L_i_ _i i i i i_ I i i TTTT r i I i i| - i~r n~~

~~6 * 0 H~~

~~* SPNLL iDQO *~~

mfid K-i £-£. %*£ s«i g-/. £•£, g-i «•/. o'B 1*8 2 "8 J I I I I I I I I I I I l_l I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I L x r M~~ oin Lfi o cDQO *

~~- - ffl rasa o e S"E: o f s"» o*s s*s Q-3 N _i i i i l i i i i l i i i i l i i i i l i i i i l i i i i l -•r—'•—•-iV" n H SH YT © 1 Q~~

~~H SH (e6)3W33KXU9dojp^qip-ex'9-^xo-lP^0!TOa-ei69 *H NMR (500 MHz, CDC13)~~

~~h-k * n I o M o » s~~

~~I ft~~

~~ft 53 p+ &s ft 53 ft~~

~~M —~~

~~254 6,13-Bis(w-ethylthio)pentacene (96)~~

~~"MrtL 45 m¥i«BH= 1838 mV] Prsftes 1-41 Snwsth Aw 20 so 398.3~~

~~+ M -CH2CH3: 369.52~~

~~«t Molecular Weight: 398.58 378.2 3?H I 20* 369. ! 278.3 338.3 oj I M,-, ji I^kl, UL 2* 260 290 3G0 320 540 38© 380 420 445 46© 489 500 «ass.*Gtaige 6,13-Bis(ff-ethylthio)pentacene (96)~~

~~UV-Vis (CHCI3) lmax at 616 nm, 569 nm and 529 nm~~

~~25- *- u 20- CN~~

~~1 5-~~

~~1.0.~~

~~0.5-~~

~~00-~~

~~353 4O0 503 550 800 653 700 WayeiengSh(nr»i) *H NMR (400 MHz, CDC13) o o o~~

~~•55- as L_ I dd 5/3 a ao ft~~

~~as u>~~

~~a o ft 53 P - s o ft 53 ft c 00~~

~~m * 1 257 13 C NMR (100 MHz, CDCI3)~~

~~ft o 53 ft~~

~~(••J o 00~~

~~1 258 *H NMR (400 MHz, CDC13)~~

*-4 — ON

~~I dd W5~~

~~o a ft o~~

~~Wl -~~

~~as u>~~

~~S3- a O ft 53 &s a ft 53 ft ^O 00~~

259 01 QZ 0C Of OS OS Of, as OS 001 BIT OJI OCX . I . . I I 1 I I I 1 I I I I I I I I I . I . . . . I . 1 . . 1 . . . ' I .... I . . . . I . I I I I I I . . I . . . . I . . . . I I I I Hoao *

~~SI U sz OE SI M SI i i i i i i i i i i i i i i i i i i i i i i i J I I I I I I L~~

~~)fiMmtii*mwi!t*iti0W^W*#H'iiwii>>*W'^l'W^itiAiiii«i»^f»i»WH.ifi*>tww> < U> \~~

~~o ™a tn m m on in HI in m sn sn~~

~~I.I..II. . I I . I I i I I . I . I I I I I I I I I I I I I I I I I I I I I .. .. I I I I I I~~

~~•***» «ta^4«%^*^. -^^V^MW^WWWVKA~~

~~H" -^ oi sv^-CK (86)3«33«l«3dojpA'qip-ex69-((>TOl^3P0P-w)s!a-ei'9 *H NMR (400 MHz, CDC13) *H NMR (500 MHz, CDC13)~~

~~ON h-k i dd~~

~~^ // I as <\ // GO u>~~

*» - "I O ^ // IS ft 53 ^ // ft 53 ft

~~1 262 13 C NMR (100 MHz, CDC13)~~

~~ON h-k~~

~~O u» I Cd e o 53- <^ 5T f~ o I JO ON o \» * h-k~~

~~o I o a o a OJ 53- a o fcfl o ft 53 O L ft 53 ft~~

~~« - o~~

~~"fl 263 6,13-Bis(ethylthio)-6,13-dihydropentacene(99)~~

~~"^S. H~~

~~%5T ',5 atyam= §49 mV) Ptafies MB Sm«* Ar 20 -tetlne » 309.3 Molecular Weight: 400.60 1001 3 .] 1~~

~~378.3 402.1~~

j 310.3 355.2 278.3 20 j 340,2 i I 3711 4CJ3J 10; oi : k I JUv >^i ii • Hi 250 280 270 280 29Q KB S10 320 330 340 350 3SQ 370 380 38© 400 410 42q ifessCtaffa 2,3,9,10-Tetrakis(benzyiltho)-6,13-bis(phenylthio)-pentacene (100)

~~o SPh U BnS SBn Q U N BnS SBn SPh o o in~~

_>LjLtA^,.J. ^JV • •• ,. Uj.* A JLWA-L fc. 1 • I ' 1—I—1—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—~i i i i i I i i i i I i i i i r I s Diethyl 4,5-Dichlorophthalate (101) um U N Cl^^^XOOEt

~~O COOEt TMS * o (N~~

~~£ w * CDC1,~~

~~JU- JU y* L»4ai~~

~~1 •p^ | | ^ p^^p^^,—"^—-J-iTTj .-JW—,w-^T^r-y-^ yi , p-^-^^^j—q p^^,^ i r t i P**™T*™*™T ™ ( i i i fpa m NMR (500 MHz, CDC13)~~

~~o - o n~~

g ft*

~~o - 1=3 a GO GO ft 53 \ /~~

~~5T > i 5T / O o o ST o ft o o w w o~~

~~•a 267 Diethyl-4,5-dithiobenzylphthalate(102)~~

~~BnS ^/^XOOEt~~

~~ro u BnS' TOOEt Q I _i 1 jJUUUl L 3,-7 ^.-aiis a.3 s 3L-3-4. a.-3-a a. 312 a. 3-»_ -*_=to 00 o CN o~~

~~CDC13 * U~~

II *^ ,N ' •» ii Trnw * t tfnr^ L^ •• I H Mlf 1»ltlB*1llM • TN^^» I I I I I I I I I I I I I j I I I I I I I 1 I j I I I I I I I I I J I I 1 I j I I I I I I I I I j I I 1 I I I I I I I 140 120 100 80 60 40 20 ppm *H NMR (400 MHz, CDC13)

~~o n~~

~~I * — w a o m - ft~~

~~s» •~~

~~dd dd i P P GO GO \ o o- ft c7 53 o n o- JX tow ft 53 o o N M — ffi ffi ft 53 ft~~

~~•X-~~

~~13 1 J 269 13~~

~~H C NMR (100 MHz, CDC13)~~

~~i MS~~

~~o a* ft 53 N o •4 O a ft o 53 N ft 53 ft~~

~~« 270 4,5-Dithiobenzylphthaladehide (104)~~

~~CDCI3* TMS * m u CDCI3* BnS~~

~~BnS N CHO~~

~~CN O o~~

~~_/\. I 1 I I 1 I I I 1 . I I I I . I I I I I I 11 I I I I 1.1 7.6 7.5 1.4 7.3 7.2~~

-L X .—iUl ^L lA^^. ~~i—1—1—1—1—1—1—1—I—1—1—1—1—j—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1— 10 987654321 ppm 4,5-Dithiobenzylphthaladehide (104)

~~u«r> Q BnS CHO~~

~~N BnS CHO~~

~~4T5 * CDC1,~~

~~J V~~

M^N^M**^* J-Jv** •W»fr^ 4*~ —i i i i I n i r- I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ISO ISO 140 120 100 SO 60 40 20 pp«n *H NMR (400 MHz, CDC13)

~~dd dd P 0 GO GO~~

~~"1 E~~

~~ft 53 «® 3~~

~~i 13 ft 53 4-t- o ft 53 ft >£ 53 m - *-• 53 O 53 ft O fa —~~

~~273 2,3,9,10-Tetrakis(benzyltho)-6,13-dihydroxy-6,13-dihydropentacene (106) H OH BnS SBn~~

~~m BnS SBn H OH * CDCl,~~

~~i-JW^—Jl r ^ . /L_aJuL_^sjJL~~

~~dd dd P P GO GO o as~~

~~Ml O~~

~~275 2,3,9,10-tetrakis(benzyltho)-6,13-bis(phenylthio)-6,13-dihydropentacene (107) H SPh BnS. SBn~~

~~c> u o u N~~

~~f- CN o o~~

~~T 1—1 1 1 1 1 1 1—I 1 ]—I 1 1 1—| 1 I !—I 1 1—I 1 I 1—I 1 1—I 1 1 1—I T" 7.8 7.7 7.5 7.5 7.4 7.3 7.2~~

~~-i—|—i—i—i—i—|—i—i—i—i 1—i—i—i—i—|—i—i—i—i—I—r- % 1 6 5 4 2,3,9,10-Tetrakis(benzyltho)-6,13-bis(4 -*-butylphenylthio)-6,13- dihydropentacene (108) um Q U N~~

~~t-- o r-- o (N s 2,3,9,10-Tetrakis(benzyltho)-6,13-bis(4^-butylphenylthio)-6,13- dihydropentacene (108) m u * CDCl ft~~

~~N BnS TMS * o BnS o 00 CN~~

~~W\IHJ ^Ju.~~

~~n—i—|—i—i—I—r-]—I—I—I—I—|—i—r—i—i—|—i—i—i—I—|—|—i—i—i—|—i—i—n—|—i—i—i—i—|—|—i—I—I—[ 7.8 7,7 7.6 7.5 7,4 7.3 7,2 7,1~~

-JL^JL hJh^V • ^thi ••' ' li *•"**' JU MM*Mf*Jv\wLfe«l JL ^^^^^«^^^ ~i 1—i—I 1—i—i r ~I I I I I I P H I 1 I r -i—i 1—r ppm 2,3,9,10-Tetrakis(benzyltho)-6,13-bis(4 -f-butylphenylthio)-6,13- dihydropentacene (108) u uft N

~~O CN~~

, A JJ 1—i—i—i—p" "i—i—i—I—i—i—i—i—r—i—i—r -]—TT—r~i—|—i—i—t—r "T I •''• T ••'••'• C •'•j'" "f •" f 7 4 3 i 9,10-Bis(phenylthio)anthracene (110)

~~r> r^N u ft * CDCl,~~

~~o oo O CN o~~

~~m u uft N~~

~~o o~~

.u.ii .^tAjihii il J II 1. I LJ li. J. L..1 LIJ]-lLij_ tl ill .. LJJ il „ iJH .kill .1 LllMl ill Li LL Ikili.. LLIni.li.Ji I IU I . l.l. i .•• p ii ji i i ' i ' "i r ' iLiiJMnkfcJjUJLJj.^iH.J^JtltftiliLLjlllnJ,..d>jiLh.JjjLMuilAil.LjiLiiJ I I 140 130 12 « 110 100 90 80 9,10-Bis(phenylthio)anthracene (110)

~~%ini )6 mV[sum= 849 mV] Profiles 1-8 Smooth Av 20 -Baseline 80 394.3 100'~~

~~90- ao- •- o 70- CN ON oo GO 60- CN~~

~~50-~~

~~40- 317.3~~

~~30] Molecular Weight: 394.55~~

~~20 31C .7 10-~~

~~0 it. 11 i>. , . 500 §00 700 800 900 1000 Mass/Charge *H NMR (400 MHz, CDC13)~~

~~93 53- ft 53 99 -|~~

~~CO 53 5T >-* n ft 53 ft o~~

~~its.~~

~~a n~~

~~283 13 C NMR (125 MHz, CDC13)~~

~~53- ft 53 vj~~

~~&S O ft 53 ft M~~

~~H •a~~

* o

~~r 284 9-(Phenylthio)-anthracene (111)~~

~~%M 13*6 IFVISJIT^ §824? n*l Pnrfies 1-13 Sraosti Aw » 80 2865 10S b r^N i a I »} oo CN~~

217.3 Molecular Weight: 286.39 J 242.5 I 254.3 I 28511 20' \ 178.3 1 193.3 2|L5 J261.2 |i| 3o?_3 Of i I - I m ;• « " 160 1» 200 221 240 X* 280 300 140 I Jv-—Uw-,—A., A-3 . WasKaarw 9-Chloro-10-(phenylthio)anthracene (112) m N * * Ov-O o * CDCl, 00 CN

~~bJ H~~

~~•g.~~

~~F n o o~~

~~287 9-Chloro-10-(phenylthio)anthracene (112)~~

Wri \ mVtsum= 23175 m>«/] PiBlfes 1-50 Swosift A* 20 -Baseline SO 320.3 1f»1 -1 » oo b CN o i a; ml 322.3 m\ 227.3 J m Molecular Weight: 320.84 209.3 228.2 242.5 284.5 301.3 152.3 3 -! I 193.3 #2.3 2|0.3 \ 2L sA.3 ^

~~0? _»_ 1—A, P—4 .i ri „r.)•?*!• ,.,. r~>»- UB tm ieo 280 320 2400 280 280 308 MO Mass Cra^ge 9-Chloroanthracene (113)~~

~~m U ft * CDCl, u N~~

~~O oo O CN~~

~~U N~~

~~o * CDCl, O o ON CN a~~

~~i WfflfI li I | I|I | i | II I IITT^ I I Ii r i i U 132 13 0 12 a 12 § 124 m~~

~~W»|lWI»i#W|il^ T 1 1 1 1 1 1— -i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 140 13© 120 110 ISO SS 80 7© ppm Mass Spectra o S _ 8 B fe S g 3 g g _ § I~~

~~I O 8 0) ^ /~~

~~~C8 0) §• w w * N> S —-8 \s /~~

~~~8 — bi W~~

~~L: \: —>> *» 2 -— U1 Fu~~

~~291 X H NMR (400 MHz, CDC13) us~~

~~m m~~

~~o ft o 53 o ft~~

•a

~~292 9,10-Dichloroanthracene (114)~~

~~N o * CDCI3 s? o CN~~

~~^^il^iUU^H^ ^^^•PP""""""""^""^ *f\. ^F^^^^^^^P"~~

~~_, , , r i—r 1—i—-|—r T—j—1—r 130 120 lit so SO PfWI 9,10-Dichloroanthracene (114)~~

~~%iai 90 s*ls«= 8*12 nrtfl Profiles 1-168 Swrt % 20 m 246.2 «• 90-~~

~~C3 248.2 ON b 1 CN~~

~~soJ o 40 ^ Molecular Weight: 247.12~~

~~as 247.2, 10 ^~~

~~o3 'Fx*JL^ , ^—^ „ „ v " -4i 225 230 235 2« 24S 250 258 260 265 WassiOmm Mass Spectra~~

*** ^ •*£? O O o O 8 3 8 i 8 OnN O +

~~J/5 C/)'~~

~~+ n 3s* 5£ in O- >"< O 53 pa • ^i p+ ft (-ft~~

~~ft- 2S ft v to 8 J 53 - GO GO ft~~

~~-1^ U>~~

~~• • O H^~~

~~II II r~~

~~296 Mass Spectra 4K* J%S £&5 e^ cs «3 e> <» ^S_S 4-^ 00~~

~~cr> 3~~

~~£ fD s n 09 0) ST~~

~~» fD era'~~

~~/en • 4» en w~~

§•

~~VOL. oS i 4>~~

~~US —k. r** CO 297 l,4,8,12,15,19-Hexa(4f-^-butylphenylthio)-6,10,17,21-tetrahydroxy 6,10,17,21-tetrahydrononacene(116)~~

~~Solvent: CHCl,~~

~~u 1.4 o 1,2 oo cu ON CN~~

~~VI a 1.0~~

~~?o.e~~

~~^max = 422 nm 0,4~~

~~0.2~~

~~0,0~~

~~31 350 450 an Wa»le*)gti(nm) *H NMR (400 MHz, CDC13)~~

~~r in~~

~~_ •B f=~~~

~~299 l,4,8,12,15,19-Hexa(4f-^-butylphenylthio)-6,10,17,21-nonacenequinone (117)~~

~~10?ra¥i8fjm=S38T6fflV| Froffel-SOiSiiiwIii~~

~~319,9 1«N~~

»i

~~•- 1523.5 o o Ji^ o Q- CO ifl VI VI C3~~

«H

~~1380.4 Molecular Weight: 1524.15 2S-J 30 L*3 1046. 1257.3 „ 1438.4~~

~~1 * *• P 0 ^ ^ !• Ms-^ .. ,-*FF-1 .- •. * 1" .' u ;• I" Jk*. ±m soo TOO an 1000 noe m 1380 1408 1500 UV-Vis Spectra~~

~~00 to~~

~~i W ft x~~

~~8 5T ^^ ft H* 53 5s 5T~~

~~I—* i 53 O 53~~

~~ft 53 ft •O S3 »<• 53 O 53 ft 301 1,4,8,12,15,19-Hexa(4W-butylphenylthio)-6,10,17,21-nonacenequinone (117)~~

~~Solvent: CHCl,~~

~~4.0x10~~

~~3.0x10""-~~

~~2.0x10"6-~~

~~6 < 1.0X10" - (N 08 c O Cl) 0.0- I 13 o 650mV -1.0x10 -~~

~~-2.0x10"6 -~~

~~-3.0x10* 1/2 1/2 E 0x=1387.5 E Red=-738~~

~~^.0x10 1 1 1 ' 1 ' 1 2000 1500 1000 500 0 -500 -1000 -1500 Potential (mV) 6,9-Bis(4'-^butylphenylthio)-l,4-anthracenequinone(118)~~

~~CO U Q U N~~

~~© oCO © CO~~

TMS *

~~il_ JIL~~

i i i i i r "I I I I I I J I I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I [ I I I I I I W8.& Qf Q5 gg 001 0ST 8§I .'.... I .... I .... I .... I .... I ... . . I i i i i l .... I i i i i l i i i i I i i i i l i i i i I i I I i.l •»•! m m*mtmwmmmm*m***4mmmm*m**\* mv mmtmi#WPT W m<«**m*#**+*mmimm

13Q3 *

3ZX 8ZT. OEX SET *€I SET iET itl Ctl *H Sfl 8tT 051 US" i i n li i ii h ii i h il i li il il i il il il i il il i il ii ii I ii ii li i ii li i ii Im i li il il m ill ii il ii i il i ii il ii il I il i ih m I il il h i ii h i ii h ii i h ii il i il il i il il i ) £ l**M*f*^*VV"'NyMW^^ fA«MSM<«M

~~6 (8XX)3«ouinb9U9D«jq;uB-i7'x-(o!il^u9qdiXxnq-;-ii7)sia-6 9 6,9-Bis(4'-/-butylphenylthio)-l,4-anthracenequinone (118)~~

~~71! »i¥(sijf]= 120B1 raV] ftttteM7&n«ftAaD-fes*«ffl 5S8i 1»1~~

~~C4 b J oIT ) Cu CO~~

~~Vi Vl m j C3 i~~

~~Molecular Weight: 536.75~~

~~4811 #3.0 435.0 525.1 I oj Ut^fmm>«)m)*Mlfm ^>^,v. , *.,y% > t i -A. Alt 4^M. .o^xV-w 3i0 » 380 » 420 460 « 900 526 540 560 580 600 6,9-Bis(4f-^-butylphenylthio)-l,4-anthracenequinone (118)~~

~~4.5 f~~

~~4.0- UV-Vis (CHC13): Xmax at 465 nm and 376 nm~~

~~3.5 u 3.0- o CU ft » 2.5- o CO vx~~

~~5 2.0~~

~~1.0-~~

~~0.5-~~

~~250 350 600 850 700 750 Wavatengthfnm) 6,9-Bis(4'-^butylphenylthio)-l,4-anthracenequinone(118)~~

~~Solvent: CHC13 2 E" 0x=1414.5 1.0x10"5-~~

~~5.0x10"6- -809mV 1 < 1316mV A/ c ~ __——-^ ^ 0.0- i— / / o ff -632mV //l513mV -5.0x10"6 -~~

~~1/2 /// ' nF Re d,=-79 /^W.0 D5 -1.0x10"5-~~

~~I i I i I i I i I i 2000 1000 0 -1000 -2000 Potential (mV) 6,9-Bis(4'-^butylphenylthio)-l,4-anthracenequinone (118)~~

~~120~~

~~100- 288.44X~~

~~< 00 o O CO H r: 80- ~® S~~

~~40 -1 1 r— -• ' 1— 200 300 400 Temperature fC) ifrcryersa^ V4.5A TA instruments l,4-Bis(4'-^-butylphenylthio)-2,3,5,6-tetra(bromomethyl)benzene (119)~~

~~CO u u * CDCl, N K o O CO~~

* J vJ J^V TMS T—I—I—I—I—I—I—]—I—I—I—I—I—I—I—I—I—l—I—I—I—I—r— -i—|—i—i—i—i—|—i—i—i—i—|—i—i—r 7.35 7,25 7.28 7.15 7.11 7.85 7.OS 6.JS

~~Ji JI_ _j_ — 1 • -iJli i 1 1 1 1 1 1 1 1 r -| 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 r -i 1 1 1 1—r 1 6 5 4 3 2 1 NMR (125 MHz, CDCL) 4- i H w O~~

~~cr d W - <^ O sr rr> «^ sr o I *>>~~

~~I «•*• rt>~~

~~P cr "I SI o o o o n fD er o cr N 3~~

V©

~~310 l,4-bis(4'-^butylphenylthio)-2,3di(bromomethyl)benzene (120)~~

~~N Br * CDCL Br o o ITi * CDCl,~~

~~jAMJ **ju*-*—f I I I I I ] I I I I I I I I I I I I I I I I I I I I 1 .A 7.3 7.2 7.1 7.9 6.3~~

~~XI jJU. 4 L-kJ L_l T 1 I | I I I I p "1 I | I I I I [ I I I I | I I I I | I I I I [ 5 4 3 2 ppm l,4-bis(4'-^-butylphenylthio)-2,3di(bromomethyl)benzene (120)~~

~~i t,* •^••'Swiil ill nimp,"Mi ||p, ifiMrt W"t*1 'I i""WI"W infill I ihTMl'H"! Iinfi* l""^"ll W"**"MIV**rW^ "~~

~~p¥*mmmn*mmwil//m}+^JP*l*mW m^*^K**+~~

~~150 140 130 120 110 10S Si BO 7Q SO SO 40 •ppm. l,4-bis(4'-^butylphenylthio)-2,3di(bromomethyl)benzene (120)~~

~~100~~

~~< CO O 80-I H CO~~

~~5» 60~~

2G 50 106 150 200 250 300 350 Temperature f C) y rsaversai V4.5A TA Instruments l,4-Bis(4'-^-butylphenylthio)-2,3,5,6-tetramethylbenzene(121) uCO Q U N a 2 o IT) J'U T—i—]—i—i—i—i—|—i—i—i—i—|—I—I—i—i—|—i—i—i—i—|—i—i—i—i—[—i—r 7.3 7,2 7.1 7.G 6.9

~~JUL i—i—i—i—i—i— T 1 1 1 1 1 1 1 1 1 1 1 1 r -•—•—r ""• 1 ' 2 l,4-Bis(4f-^-butylphenylthio)-2,3,5,6-tetramethylbenzene(121)~~

~~CO u ft U N~~

./v. — .A »—._ i -.^ 1 i • ' • ' i • ' ' • i • • ' ' i • • • • i • ' ' • i • i • > • • I . • • • I • • • • I • • • • ise 14 a uo lie no mc m m TO 60 50 m JO 20 pfm 5'K S'Z @'f S"» I , • I • _i_L j i i i—i—i—i_ • i • i I , , i .... i . l i , , i l , TT ^%j . TT" 1 w

~~«!"£. m"l Ol'i Sl"£ 0S'£ SC*i OC'i St'L i . J I I I I 1 1 1 1 1 L I . J I 1 1 1 L _l I I I I I I I I~~

z (^^X)^^ «3q-l^3«iip-e'z;-(0!q;i^u9qdi^nq-;-it7)sia-t7'x m as BS m 06 001 SIT mx OST I 111! I I I I I I I I I I I III I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ,i, , ,, i ,

~~I3Q3* n~~

SZl 85T OO Ztt KT SET SET fltl CU ffX SH BJ1 SST l. •. 111 • • 111 • 111 n 111111 • 11 • i • l • i • 11111111 • • '• 111•i• in11111111II1111••• 11• i•111111111111•i•11111111111111111111111111111 • 11•• • 1111111

•""V" *

~~ls>~~

~~N n o n~~

~~I 6 (33X)3«3z«3q-1^9« !P-e 3-(0!qil^ii3qdiXxnq-;-/t7)sie-t7'X m NMR (400 MHz, CDCL) o o o~~

~~cr N~~

~~fcs>~~

~~318 13 C NMR (100 MHz, CDC13)~~

~~o «4 o sr n ^L cr fD N fD :: fD~~

~~319 m NMR (500 MHz, CDC13)~~

~~i a fD sr cr fD 53 N fD fD~~

~~320 13C NMR (125 MHz, CDCL)~~

£3

~~cr ©~~

~~id •~~

~~-*• fD o & Q 5 fD N fD S3 fD~~

~~3 -~~

~~321 l-Amino-4-bromo-2,3-dimethylbenzene (125)~~

~~CO ft~~

~~N NH.~~

TMS *

~~.1 HI I^I'I i -i—i—i—i—i— "T" 1 13 C NMR (125 MHz, CDC13)~~

~~i a rs *-fD• 8 3 cr fD 3 N fD B fD~~

~~323 *H NMR (500 MHz, CDCL) u-i~~

~~•J o~~

~~S3 ©~~

~~in si m~~

~~«n o fD -3 sr~~

~~fD S3~~

~~•ci 0 Is) En as 'fe. if~~

~~324 N-(4-bromo-2,3-dimethylphenyl)-acetamide(126)~~

~~CO NHCOCH, 0 uft N~~

~~u * CDCl, CO~~

~~i o- 3 fD sr~~

~~tr fD | i O fD & 3 a fD~~

~~326 iEd~~

~~^WF^WB™M«^~~

13Q3 *

~~H303HN~~

~~(LZl) 3P!uiB;93V-(l^«3qdiXq;9uiip-e'z)-M s 8 S J I I I I I I I I I I I I I I I l_ I I I I _l I I I I I I I I I I L T "HN" • "• ' 'V •••~~

~~13Q3* fid~~

~~© 00 ©~~

~~fifi N n o o~~

~~1 1I3l d 6 (8ZT)3noumbauaoB|uad-ei'9-(°I llI^ l lAnq-;-4rtBj;9X-xx'8^ I 08 001 QZX §*X 031 08X~~

~~i i l i i i i I i i i i l i i i i I i i i i I i I I I I I I I I I I I I I I I I 1 I I I 1 I I I I t I I I I I I I I I I I I I I I I 1 I III I I I I 1 I I mm¥mmmwmm** I~~

~~SSI iSI 821 €?E OCX I£T £EI SET fCI SE1 SEX LIT .. I .... I .... I .... I .... I .... I ... ' ! | | | | ! | '.' I .... I .... I .... I ' fWWfW^~~

~~3UOU nb91I93B 1I3d 6 6 (8^X) ! ^ -ei 9-(o!q^ii9qdiA>nq-;-4t7)Bj;9x-xx 8^'l l,4,8,ll-Tetra(4'-/-butylphenylthio)-6,13-pentacenequinone(128)~~

~~%M. 4?1 IBV[SJTP Mm mV) Profiles 1-44 Sraocei to 20-BessiaeSI 965.0~~

*- +* 70-; o 319.8 o CO -i CO CM 50 j vx ] i 30 • 321 8 3 20- Molecular Weight: 965.40 gste 10; 304J 3518

~~f.fafaUjfan.&i i .I i rfa»jitewL«v^^*.w^V^^T^ J^>sa 350 « 450 500 » TOO m 9» 950 1000 l,4,8,12,15,19-Hexa(4f-/-butylphenylthio)-6,10,17,21-nonacene(129)~~

~~386 m¥lstfn= 181245 fa¥j Profiles 1-416 Smooth. Pa 20 -Basefie 80 287.4~~

~~CO 2S8.5 CO~~

~~i Vl SO; #1 Molecular Weight: 1464.18~~

~~30 J 21W 2&i 291.5 1483.3~~

~~-,miwiiiimim>M*mm**mm>(MmmMmwmmMa?M HAAJA. 400 500 i» 900 1000 11 1200 1300 V *H NMR (500 MHz, DMSO-d6) aC_~~

~~Cu { ^ "I o ^ I } ON *> - c I—k I \ // a- o X o*i ft \ // ns o&s \ // ft S3 re i //~~

~~a * K ffi in O o * r~ 332 6,17-Dihydroxy-6,17-dihydroheptacene (137)~~

~~ma. 83? roVfs«= 25S47® «t¥| Prafia 14MB SmeoS* Av 20 -BasHine 80. b -j~~

~~+ 60-3 M -OH = 395.48 OH + i M -2 x OH = 378.48 Molecular Weight: 412.48~~

~~80: 158.8 40:~~

~~20i 1 2557 1(1.8 223.8 „-,_ to- i 2377~~

~~o: ^,4„.,..r4..^. ••,,!PSH•< . "V 130 MO ISO 180 MS 2» 240 ^Ml)3»MI3i»li 4« 440 460 MassCtiarge 8,19-Dihydroxy-8,19-dihydrononacene(138)~~

~~%fat 2?rtVfsiirn= 1KK2ml/f 512 4 1001 j 31S6 b .j 478.3 o co CO 1 495 4 a 80- 1%~~

4 Molecular Weight: 512.60 + 1.8 M -OH = 495.6 462.3 30- + •i 1 M -2xOH = 478.6 aoj 314 f]' 1 ,311k If 330.2 364 1 3812 o: •sk^&lfes 320 340 400 «0 4*0 4» Mass-Claraa wtfd g*£ s'£ e*s s-» @*g 5-3 0" 9 5 "3 ®" £ 5"t O'B I I I I I L_l I I I I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I—I 1—I I I 1 I I I I I—I—I—I—L —, r*\ ^ r

~~3 O H* 03 O 1 a~~

~~(XH) 3U99BXU9do.ipAqiux9X -pl'Zl'L'S-£X0*VfoVsW±-pl'ZliL<'S 7,16-Bis(4W-butylphenyl)-5,9,14,18-tetrahydroxy-5,9,14,18- tetrahydroheptacene (145)~~

~~323 mVfsw- 1«1 si¥| RraEes 1-3? Sffloo8iAv2D -Basel* 80 719.5 100^ 287.7~~

~~vo CO ft 7G- CO~~

~~VI I VJ~~

~~i 219.8 M+-OH = 693.9 M+-2xOH = 676.9 i 693.2 \ Molecular Weight: 710.90 w2* 319.7 676.4 I 479,2 594.5 637.4~~

~~> r^r~v***i<»~*j*^^ ji^ i ^'tH^-Wiafj. m 460 sew m m Mass Spectra~~

~~8 S-^3 6-jjS 6JJ3~~

£1

~~337 UV-VIS Spectra of 9,10-Anthracenequinone (133), 6,13- Pentacenequinone (23), 7,16-Heptacenequinone (134) and 8,19- Nonacenequinone (135) in Concentrated H2S04~~

~~4- Anthracenequinone (187) CD O Pentacenequinone (23) '- c CD 3- .a Heptacenequinone (188) o Nonacenequinone (189) oo CO < CO •D • unit CD N 2- a To E~~

T T T 200 400 600 800 1000 1200 1400 1600 Wavelength (nm) n ^—-—— > UV-Vis Spectra © 5 fS B < & Normalized Absorbance ^ a) o C/J ^ ^ N3 CO ^ CD o o i b Ol b o b ^i *+•n _l_ _l_ _l_ _L_ _1 l_ V* _L_ h^ P>-Ss -* o rt> ^°oo GGO o^-; >»> B- s o ' :> ?P B 5 ^ np*s- &S i-S o a o O o 00 rt M CD 3 ^ < **• 1 CD_ « 00 3 o as CD c Z X "0 i—i o 3 CD CD n i—^ 1-+ o U) ICQ 3 "O 3 u> 0) i—i- <—i- © ^1 i 0) 0) 3 o O o CD o o a 3 o ' CD r& B- o Z3 13 3CD 3 3 CD CD CD Q. i-S Q. CL 00 i-S ro O o" o" o --»I— * o o ~~ "' ^^ f ^ a • h-' H* 1 3 V© VO ^ ts> H* **• o B- as o ^ ro O 3 •ai fD o o o & ^J *< ^ i 00 SJ ^1

~~i i~~

~~339 Plots of ^max-Values at Longest Wavelength of Solution of Acenemonoquinones (Red), acenediols (Blue) in Concentrated H2S04 and Reported Xmax of Acenes (Black)~~

~~Acenemonoquinones (133, n=3) (23, n=5) (134, n=7) (135, n=9) O Acenediols CO (136, n=3) E c (24, n=5) (137, n=7) c< (138, n=9)~~

Acenes R = 0.988 (Anthracene, n=3) R = 0.997 (Tetracene, n=4) (Pentacene, n=5) (Hexacene, n=6) (Heptacene, n=7) n (number of linearly fused benzenoid rings) [60] Fullerene adduct of o-quinodimethane (164)

~~Wnt 36? mV<5um= 58351 mW] RroHes i-159 Srr«* Pv » -Ba 720.8 t«1~~

~~•- -^ u cu Molecular Weight: 824.79~~

~~CM m 823.4~~

~~301~~

~~718.8~~

~~60® /OO 800 1CO0 1100 1280 *H NMR (500 MHz, CDC13) C/l ^•^ <^ O ^•^ *1 3 ^^ •roi rt» B rt> ^ f &a 3 rs aN*« <-f ^ o en o B- >-»* u B n ^1 U> \# T3 ^O r& h-^ B O o B "1 ro as H^ E~~

~~i i~~

~~VJ I—^ U>~~

342 waa 09 «£ m m OOT «' ozx ati eti 851 091 J i i i i I i i i i I i i i i I i i i i I i i i i I i i i i L J I I I I I I I I I I I I L i I i i i i I i «*WNWWN*lftftlMWrt|il 4#M«Wi»Mlll*WMHM«|^^ ttmpmi* •MM** ~ rmr i Til *lDQ3

~~odd g zx SEX SET mi S*T ssx _i i I I i i_ _J I I I I I I I I I I I _J I I l_ _l I L " l'*ll'PI^Jr,P^,?VlJ(^|W|l rttfdm^M***** mmtobWW^^ C/l~~

* p-*-

~~(t^Ll) 3U99B;u9divCu9qdip -ei'9"(l^9UI^xoi^zii9q)spiBj;9x-0l'6'e'3 J° P^ppy 9U9.i9nni[09]sra Bis[60]Fullerene Adduct of 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13- diphenylpentacene (174)~~

«»VN»=. Iifiio7 mVI Fssfes, i-3£» feaota fe»-testa e « 911.5 Molecular weight: 2352.33 b »i MW-2xC60 = 911.13 ft 5 to] 499.3 Vl ml 470 vx j f I 50-] *•* 3 469.: 7205 30- Si IJ 407.1 ©97.9 il H 379. 1 7€ i IW 5924 •I" I P 830.8

1 V2SX ,,few« 256 30© 350 iOO 4S3 9» 550 « 658 ?«S J3Q 880 850 W0 950 msM S'l. 0*S S*S 0"9 5*9 0*£ S"£ 0-8 J i i i I i i i i I i i i i I I I I I I i i i i I i i i I I I i i i I i i i i I i i i i_ nr

~~i i i I t i i i I i i i i I i i i i I t i i i I i i i i I i i i i I i i i i l i i i i I i i i i i i i i t I i i i i it i• i• i• nw r~~

~~o a URO URO N o o loao * o~~

~~URO URO~~

~~(SLl)3U33Bl«3dl^U3qdIP-€l'9~~

~~OBn OBn * CDCL C}~~

~~OBn OBn N LJU •sT im 130 12fi pp>£a~~

~~^^X^MJ^^m* •»• ,iW ri"^TiiiMip*-^^^j^niniLnîi 11 <*t 'I Pll, Î'l • •^•ilNll! ti. V I| 10IM » I •*! I I I I I Vi^^^pî~~

~~—1 1 I ! ! [— "T 1 1 1 1 1 1 1 1 1 1 1 1 1 1 r —]—i—i—i 1—|—i—i—i 1—[—i—r 140 130 12§ 110 100 ss SO ?» 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenylpentacene(175)~~

%irl 337.1 100" 1 OBn p^ OBn so- 3812 I . - 1 . . J C5 1 Y^^r^^Y^^^r^^r b 3 J.L o 7G- QJ t If /^^^^x^*^^^^ Q. ®SS- '' 1 p1h VI S© 1 [ OBn OBn VA ! * 31f Molecular Weight: 911.13 2a§1 | 463.2 ° 38- 3CE;1 i 4jfe.1 2S* ii 11 I. . 911.1 165.1 j. In 1 AUM? j £ lH. ^,« 11 • • Mi - JH ™ e .TJiiM If. Mjliif^^ i 230 300 «© 560 600 ?€» SB 900 1KB toss/Owge 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenylpentacene (175)

~~T 1 1 1 r 350 400 450 500 550 600 650 Wavelength(nm) cp346-0sec sre:cp346:Cycle01 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenylpentacene(175)~~

~~ON *-f~~

Wswlwgthjnn) -cp346-1-0sec sre«p34e-1-Osec -cp3461-30s8c sre cp34S-1-9Qs€C cp346-1*30s€C sre.cp346.1-30sec -—cp3461-SOsec sre cp346-1-BQs€c cp34b-4mn sre cfS4S-4mn sre — cp34S-8trsir sis cp346-8mm cj»j4b-*ffli sra cpJ4>Sm»n — ep34b limn sro cjjJW6-l2mir -cp346-l-i20sec?*e ep348-M23sac — cp34S20mn sre cp34B-20mir -gp346-13min «r« ep34G 13min — cp34&1Cmo we c|»346-1G«rai -cp346 17mm are cp34617*nin — ep346 24m n sre ej)34S 24mir - cp346-25mm sr# ep3

~~•- o a o m~~

an Wavatenqthtnm) -wMS-Qssi, STB i346-0**t ' k34e»24rrafi srt i346-25rr in — „34§-4i!rnn ss«1,348-SirHfi - c346 STUD sra c34E~9twi c34S-12mifts« c346-13srif, -— :34&-16mm sra c34S.17mm c34S 20mm OKJ c3*6 21 mn c34€ 28r»mw« c348 TSmvtt — S346 32miii sre c34633wn -e346-36min sre c346 37mm -C34g-40rr«isre c348-41jrin — ;346-34raifl sra c346-95mn -c346 44mm »e c3£S 4Smp -c34&^8r»msr« c3484?n"ir — r34S-S0fflin sft c 346.51 mm ~i,34S-S3srafs s*« i^sc-Stoim -CMG-fiQrun w* c34IMs1rnn — ,348-30**^ sf* (,346-80**.,, c34Bfi4miii ste c34frfi5inm - c34£-74min sre c348-75rnii :346-34ffljR sre cp34B»8£min e34S 94mm,3ie ,»3<£S 56mw 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenylpentacene(175)

~~1/2 4- E 0x = 636 mV~~

~~< H~~

~~-i—< C (1) s_ j— o -1360 mV~~

~~1/2 E Red = -1398mV~~

~~—' 1— —1 1 1 1 1 1 1 1 1 r 1500 1000 500 0 -500 -1000 -1500 Potential (mV) 3,4-Bis(hydroxymethyl)furan(176)~~

~~HOH2Cx > HOH2C~~

* CDCl,

~~J TW*» ri -» f ^ ^ ^J l—i 1—i 1—i 1 1—i 1—i 1 1—i 1—i [—i 1 1—i 1—i 1 1—i 1—i 1—i 1 1—i r- i—|—i I—I r—i 7.5 7.d 6.5 6.0 S.S 5.0 4.S 4.Q 3.5~~

~~352 X H NMR (400 MHz, CDC13)~~

~~- * n a n~~

~~i dd~~

~~o- x /- O dd \—/ dd P ft P 0 L~~

~~353 3,4-Bis(benzyloxymethyl)furan(177)~~

* CDCl, m OBn

~~N pa m OBn tf~~

~~y-^U/ * 'Jl li,H|. |M~~

~~T—i—|—i—i—i—i—|—l—l—l—l—|—i—r US 12S 127~~

~~• 11 ^jA*w******M*^w*»pr^iiii n*Mih »» ,**'**l*«l»HlHlHfcwH*lllWl>III^IHl|lMl»HHn^»*ll»M» **"' *rV*wAnt»lHpi»»>*iiid W»l|ll»>W~~

i' ' ' I I I i I | I I I t I I I I 1 I I I I I | I I I I I I I I I I I I' " I"' 140 138 120 Hi 100 Sfl 80 70 3,4-Bis(benzyloxymethyl)-7-oxabicyclo[2.2.1]hepta-2,5-diene-2,3- dicarboxylic acid dimethyl ester (178)

~~N OBn ffl C02Me ir> CO m XJC Si f C02Me * CDCL OBn * 1 .Lim~~

-i—i—i—i—i—i—i—i—i—j— -i—j—i—i—i—i—]—i—i—i—i—|—i—i—i—i—|—i—i—i—i—i—i—i—i— 7.0 €.S 6.8 5,5 5.0 4-5 4.8 EPas 3,4-Bis(benzyloxymethyl)-7-oxabicy cio [2.2.1] hepta-2,5-diene-2,3- dicarboxylic acid dimethyl ester (178)

~~OBn * CDCl, C02Me~~

~~C02Me~~

~~1. I I.. . I ... 12S.0 127.9 OBn~~

~~•^ w sr * o o o p 53 -o dd (Jl I~~

~~^ wa"~~

~~fD o o to to ST a> n> 3 fD cr~~

~~MS. & Ml fD~~

~~N fD~~

~~357 13 C NMR (100 MHz, CDC13)~~

~~I w vx m —~~

~~U1 — o o o~~

~~o 3~~

~~(Jl i C~~

~~O ^ fD 3 H 8 O r/ f o o ST to to CD CD a fD a. o * - — o a a fD N fD 53 fD~~

~~358 *H NMR (400 MHz, CDC13) Is) SI I dd VX a o >-« o p 3 fD~~

~~4-^ \* (Jl i a- VX /Si fD c 53~~

~~359 l,2-Bis(hydroxymethyl)-4,5-bis(benzyloxymethyl)benzene (180)~~

~~CO OBn OH u * CDCl, uO N~~

~~o IT) CO~~

~~138 136 137 136 13E 134 133 132 131 130 123 138~~

~~pA-^^fW M#tvfS* \iiKtA-*')V^//it**T^^ WKSA^Y*^ 1 I ' "T I I I I I I I I I I I I I I I I I I T" 1 I ' n • r -|—I—I—I 1—I—r 14© 130 120 110 188 SO 8§ 70 *H NMR (400 MHz, CDC13)~~

~~(Jl I dd *-• O & dd fD P 53 N *^< w ST o o 3 fD v53--~~

~~i o- fD 53 O N fD O 53 O fD a *-• o~~

~~p a fD 53-~~

~~0a0 fD~~

~~361 13 C NMR (125 MHz, CDC13)~~

~~i dd VX o —v ^- -o 'a* dd v dd fD 53 -V P H 53 O ( > ST rT -< ffi ffi 3 o o fD H U1 o~~

~~.6. I a* fD 53 N fD 53 fD a rs a*i - oH H o o a& fD 5T o fD~~

~~362 usfid 6"S S"S 0"9 S"3 »"£ S*£ 6*8 S'B I I i i i i I i i i i I i I I I I i_ I I I I I I I I I I I I I I I I I 1 I I I I 1 I I L. f*~"V ~v ~Y 1 }~~

13Q3 *

~~URO URO~~

(Z8X) 3uouinb9U93B;u9d-£x'9-(l^m3tti^xoiAzu9q)sp[Bj;9X-0Xt6'£6Z 13 C NMR (100 MHz, CDC13) o- -o N> w dd p P _/ o y 1 fD •1 -4 — 4} o= =o E sh — cr o fD P ( 01 — } © ST i } s o •O fD dd dd MS — P O P

~~U> i fD P <^ n fD P fD o -D o 3 P n P P * fD 00~~

~~364 Mass Spectra~~

~~i i ^ o an ° Q w ffi 5* W G- •1 to )-r' ^ II K VX II OO <-* .-* "cr fD "-J ON P N ST~~

~~3 fD <•*• 69 15 P- Q as -o u> m 1 P ^3 fD y j> P~~

~~\_ fD g' _} P =o fD~~

~~5 09 CO P \ J P P P %_ J fD O- -o H* td w 00 S3 P ts>~~

~~365 2,3,9,10-Tetrakis(benzyloxymethyl)-6,13-diphenyl-6,13-dihydropentacene-6,13-diol (183)~~

* CDCL

~~CO o o m~~

*b^irf^^^M-^^^r IU«*^ vW "*•»» ^^*T**i^MP.^Wr^"^^" I" %• M^*****. I N'l •**«* • tfj^IW " uti Mp irfl »iHW|

~~CO * CDCl,~~

~~l> m CO~~

~~U .^•Xw'Uwdw'**^ I 1 ' i 1 I I ~ -i—i—|—i—r n i i n -i—i—i—r T i i n T I i ~ 140 110 120 lie ISO so 80 7§ ppm Mass Spectra~~

~~368 waa o- i z £ . * SSL j i i I i i i i I i i i i I i i i ' I i i i i L I ' i I I I I I i i I i _i L~~

~~^*—— ii * .•.. «^»^^0V ^w^«"*^^^WH"* '* S1ALL 1 0"£ Z'l VL 9"L f£ I .... I .... I .... I .... I .... I .... ' .... I .... I .... I . .~~

~~4^ O O~~

~~N o~~

~~:(j78X) 9U99B;u9d|^u9qdip -ei'9-I^*3raoP°!*JW-0l'6'e'Z J° l3nPPV aujuaimtf [09ls!9 13 C NMR(125 MHz, CS2/acetone)~~

~~Acetone s - C dd ^•d* vx O F~^ m o> ^•O^ *1~~

~~^••rP i ^^ fD *S fD P fD ft > T3 ft P- ft fD P P ^•ri Hi n T3 fD o^s P N> rt- \» to U> n fpD 1—k ttl fD o ^~v e-K 1—^ fD 00 p*- J^ *! • • &^^s« P ft o~~

~~370 l,2-Di(iodomethyl)benzene (187)~~

~~CO u~~

~~O o m * CDCl,~~

~~M ^*, LL TMS * ->—r 2 ppis 13 C NMR (100 MHz, CDC13)~~

~~H • k w - C~~

£5

~~e • o p 3 fD o ^ p Q X X h^ h—i i—i oo~~

~~372 Z £ fr § 9 _i i I i i i i L . . . I i i i i I i . . . L _J I I I I I I I I~~

~~i *~Y ffl~~

SPNLL \DQ3 *

~~O O~~

~~N n © n~~

~~(06X) «POxoip[|76x] |j'q]ozu9qip-ojpA'qip-xxt9 13 C NMR (100 MHz, CDC13)~~

~~t^i —~~

~~HI *» — o>~~

~~a i-S p~~

~~H» cr fD P N O H1 H cr~~

~~ft o ©~~

^©

~~374 1,4-Benzene diisoindoline (192)~~

~~%int 1425 mV[sum= 712422 mV] Profiles i-500 Smooth Av 20 -Baseline 80 311.9 100;~~

~~90- a \ // '- 80; +^ u 70- Molecular Weight: 312.41~~

~~ft 60- CO 31 3.0 vx 209.9 vx 50 31(1. 8 40: 205.9 30-~~

~~20; 192.. 9 164.9 10; 1 .9 3 0 k. ,H-. P i i 4* ^-4 ijaiii^ 140 160 180 200 220 240 260 300 320 340 360 380 400 420 Mass/Charge 2,3,5,6-Tetramethyl-l,4-benzene diisoindoline (193)~~

~~ii mV?acn= £W mV; rtwhtes i-SW ikst* tet "Si -teefc« M 366.0 1001~~

~~90 \~~

~~80-" \\ // 363|S b I o ro] 204.7 263.8 ft CO ml Mcjlecular Weight: 368.51 vx vx 50~~

~~MX I 30 : 2S19 303.0 ! 1 ol -u.ti. Tl T V .ll, , 1i80 200 220 240 260 280 MO 380 340 360 W3 meaawm [l,r-Biphenyl]-4,4'-diisoindoline(194)~~

~~M<* mr «¥[&«= 12»P? ravi p»of3es i-t** SUXWBI m m Ssssino as 388.1 »i b 30-~~

~~ft- E~~

~~o 3 o a~~

~~I ft~~

~~C71 m~~

~~378 l,2,4,5-Tetrakis(bromomethyl)-3,6-dinitro-benzene (195)~~

~~7 1 tnV;SUBI= 898 mV] RroBas 1-99 Smsoft Aw 20 - »as NOn 458.6 100] I Br Br 4fe0.6 Br Br~~

NOo b ml 4430 Molecular Weight: 539.80 i 4932 u ml 537.1 ON ft i co in Vx vx a H 473.1 4p-6 DUi508.p-9s i 5531 570- 0j 410 420 430 **0 450 460 470 480 430 9M> 510 S20 530 54© SSO » 579 l,2,4,5-Benzenetetramethanethiol(198)

~~TMS * CO~~

~~N o oo CO o~~

* CDCl,

-JU_-J- i/^14M_ te^Ata^ta*«******tar«V -Ujlu T 1—|—i—i—i—r ~l—'—r H I I I J I II I | I I I I | ~i I i | i i 5 3 2 1 ppm ™M 0£ Qf os 09 Oi. 08 06 OEJT Oil SSI OET On _i i i i I i i i i I i . . . I . . . . I . i i i l_i i i i_I . . . i I . J I I I I I I I I I I I I I I I I I I I I I I L

~~I. I ' 1 ' f I "f* •" T nw 2~~

~~1DQ3 * 00 (Jl~~

~~N n n~~

~~(86x)i°ro3UBlP9mBjJ9J9uazu9a"SVz'x >H NMR (500 MHz, CDC13) £=~~

~~_ * • 1" * >1 SI 1 o SB O m - o >= o E~~

~~m - 43 as . w —J ' "" Ml _ cr w r cz v_ cr ft i-S o~~

~~h-k r O 382 Mass Spectra~~

~~ft p 3 K~~

~~2 S3 S3 N~~

fD o 3 *

~~o- ^o 2^ \ 3 o \\ // CD Q 8 ffi fe- V //ffi ^ °v v° cl K' -CK •& \\ // ^1 ^ /^ 4^ vo O- ^O ~j CO 0 0w~~

~~383 2,3,9,10-Tetrakis(benzoyloxymethyl)-6,13-dihydropentacene-3,3'- bisthiopropanoic acid (211)~~

~~OBn C°2H OBn H. S 'd *H20 i O *DMSO m~~

~~N OO CO o o~~

~~0* —A -feh -IS j*IP"~~

~~> 2 :^ >£»~~

~~(31~~

-S

~~385~~