Evolution of the Optical Spectra of the Acene Homologous Series: Neutrals and Dications up to Undecacene Dissertation der Mathematisch-Naturwissenschaftlichen Fakultät der Eberhard Karls Universität Tübingen zur Erlangung des Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) vorgelegt von M. Sc. Bin Shen aus Anlu, Hubei, China Tübingen 2018 Gedruckt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät der Eberhard Karls Universität Tübingen. Tag der mündlichen Qualifikation: 07.06.2018 Dekan: Prof. Dr. Wolfgang Rosenstiel 1. Berichterstatter: Prof. Dr. Holger F. Bettinger 2. Berichterstatter: Prof. Dr. Martin E. Maier Acknowledgments First of all, I wish to express my deep appreciation and gratitude to my supervisor Prof. Dr. Holger Bettinger, for giving me the opportunity to get into research in his group, and providing me with ideal working conditions. He is an easygoing professor, and I enjoy the freedom in working under his guidance. His constant support and encouragement inspire me throughout my PhD study. I am truly thankful to Prof. Dr. Martin E. Maier for his kind help of revising my thesis. Special thanks to all the group members (Florian Reicherter, Thomas Geiger, Christina Tönshoff, Klara Edel, Małgorzata Krasowska, Ralf Einholz, Peter Grüninger, Jennifer Hahn, Constanze Keck, Florian Höse, Michael Fingerle, Andreas Göttler, Matthias Müller, John Bauer) in the group for their kind help and the pleasant research atmosphere they created during my PhD. Additionally, I thank Thomas Geiger and Florian Höse for helping me with the translation of ‘Kurzzusammenfassung’. Moreove, I also thank Constanze Keck, Maximilian Winkler and Dovilė Rudalevičienė for their help during their practical courses in this group. I would also like to express my gratitude to Mr. Walter Schaal for his patient help on repairing the UV-Vis spectrometer, which made me obtain nice UV-Vis spectra in time. I am very grateful to Mr. Paul Schuler and Dr. Markus Kramer for their help on measuring NMR and EPR. I also wish to thank the China Scholarship Council for the fellowship. Last but not the least, I would like to mention and thank my family. Without their support and understanding, it wouldn’t be possible to achieve all these. Table of Contents Table of Contents Abbreviations .......................................................................................................................... III Abstract .................................................................................................................................... V Kurzzusammenfassung .......................................................................................................... VI 1. Introduction ....................................................................................................................... 1 1.1 Introduction ...................................................................................................................... 1 1.2 Structure and Reactivity ................................................................................................... 2 1.3 Acenes larger than Pentacene ........................................................................................... 7 2. Objectives of this Thesis ................................................................................................. 13 3. Synthesis of Undecacene Photoprecursor ..................................................................... 15 3.1 Introduction .................................................................................................................... 15 3.2 General Synthetic Approaches to undecacene photoprecursor ...................................... 16 3.3 Attempted improvement ................................................................................................. 21 4. Photodecomposition of Acene Precursor in Polymers ................................................. 25 4.1 Introduction .................................................................................................................... 25 4.2 Photochemical synthesis of undecacene 4-1 .................................................................. 25 4.3 Conclusion ...................................................................................................................... 30 5. Generation of Dications of Nonacene and Undecacene ............................................... 31 5.1 Introduction .................................................................................................................... 31 5.2 General approach to photodecomposition of acene photoprecursors in solution ........... 32 5.2.1 Photodecomposition of pre[9]acene......................................................................... 32 5.2.2 Photodecomposition of pre[11]acene....................................................................... 34 5.3 Generation of nonacene dication and undecacene dication in 96% H2SO4 .................... 35 6. Investigation of 2,3,9,10-Tetrafluoropentacene ............................................................ 43 6.1 Introduction .................................................................................................................... 43 6.2 Computational Investigation of the Removal of an Etheno Bridge ................................ 45 6.3 Photochemical Synthesis of F4PEN ............................................................................... 47 7. Experimental Section ...................................................................................................... 49 7.1 Instrument and Reagents ................................................................................................ 49 7.2 Computational Methods ................................................................................................. 49 7.3 Synthesis of the undecacene photoprecursor .................................................................. 50 7.4 Synthesis of the substitution 3-11 ................................................................................... 53 7.5 Photogeneration of undecacene 4-1 ................................................................................ 56 7.6 Synthesis of the dications of nonacene and undecacene ................................................ 56 7.7 Synthesis of the F4PEN photoprecursor ......................................................................... 57 8. References ........................................................................................................................ 59 I Table of Contents 9. Appendix .......................................................................................................................... 65 10. Cartesian Coordinates ................................................................................................ 75 Curriculum Vitae ................................................................................................................... 99 Publications ........................................................................................................................... 100 II Abbreviations Abbreviations PAH Polycyclic aromatic hydrocarbons OFETs Organic field-effect transistors OLEDs Organic light-emitting diodes OPVs Organic photovoltaics HOMO Highest occupied molecular orbital LUMO Lowest unoccupied molecular orbital Ea Activation energy E0 Sum of electronic and zero-point Energies NICS Nucleus-independent chemical shifts PMMA Polymethyl methacrylate DFT Density functional theory MRCI Multireference configuration interaction UV-Vis Ultraviolet–visible spectroscopy PEN Pentacene PFP Perfluoropentacene F4PEN 2,3,9,10-tetrafluoropentacene n-BuLi n-Butyllithium MeLi Methyllithium TEMPO 2,2,6,6-Tetramethylpiperidine-1-oxyl NMO N-methyl-morpholine N-oxide HRMS High resolution mass spectrometry NMR Nuclear magnetic resonance TMS Trimethylsilyl OTf Trifluoromethanesulfonate III Abbreviations TBAF tetrabutylammonium fluoride DCM Dichloromethane THF Tetrahydrofuran MeCN Methyl cyanide PS Polystyrene NIR Near Infrared eV Electron volt APPI Atmospheric pressure photoionization ESI Electron spray ionization TS Transition state DA reaction Diels-Alder reaction DMSO Dimethyl sulfoxide IV Abstract Abstract Acenes are a series of polycyclic aromatic hydrocarbons built up from linearly fused benzene rings. Undecacene, the largest member of the acene family to date, was generated in polystyrene matrix under cryogenic conditions from a photoprecursor with two α-diketone bridges. The electronic absorption spectrum of undecacene contains two strong absorptions in the UV-Vis range. The optical gap of undecacene follows the trends that were observed earlier for the shorter members of acenes. The optical gap of polyacene obtained from an exponential extrapolation is 1.23 eV. In addition, the dications of nonacene and undecacene were generated and investigated by dissolving the products of photodecarbonylation of α-diketone precursors in concentrated sulfuric acid. The exponential extrapolation of the optical gap to the limit of infinite chain length of the acene dication series (from tetracene dication to heptacene dication) arrives at 0.99 eV, in accord with the value obtained from data up to nonacene dication (0.98 eV) and undecacene dication (0.93 eV) respectively. Moreover, the tetrazine induced synthesis of 2,3,9,10-tetrasubstituted pentacenes from 6,13-etheno bridged precursors was studied computationally. The computational investigation of the mechanism and energies