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Design, Synthesis and Properties of Corannulene Based Blue Emitters and Carcerands Design, Synthesis and Properties of Corannulene Based Blue Emitters and Carcerands By Praveen Bachawala A Dissertation submitted to the Graduate School of University of Cincinnati in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Department of Chemistry McMicken College of Arts and Science Committee Chair: Dr. James Mack Abstract Corannulene (C20H10) – a curved polycyclic aromatic hydrocarbon synthesized in 1966 purely out of curiosity was synthesized first by Barth and Lawton to test the theory of aromaticity laid dormant until the discovery of fullerenes in mid-1980. Similarity in structure piqued the interest of researchers to find simpler route towards its synthesis which reached its peak in year 2000. Recently, corannulene was reported to be synthesized on a kilogram scale. However, its potential application for high emittance, thermally stable blue emitter needs has been limited. Major part of my thesis (chapter two) focuses on this aspect to examine the outer rim of corannulene and target which sites resembles more like ortho/para vs. meta unlike benzene. Functionlization of such sites with acetylene bonds would immensely help in designing highly efficient blue OLED’s with great thermal stability. We have identified two sites over corannulene’s outer rim 1,8 and 1,5 and functionalized them with acetylene bonds to extend conjugation of corannulene’s π-aromatic framework. Further enhancement in conjugation was possible by tethering terminal ends of acetylene bonds with chromophores such as phenyl, anthracene, corannulene and biphenyl to study absorption/fluorescence. Later data obtained was used to excite molecule with proper laser to examine their ability to emit intense blue fluorescence. Chapter three focuses on our attempts to find out how the structural changes of the linker length would contribute to better understanding the aspect of conjugation and its impact on the overall bulk photophysical properties of corannulene based materials. Such study would help us identify the right proportion of linker length needed to exhibit effective conjugation with corannulene and result in designing a blue emitter with robust potential. Chapter four demonstrates the use of corannulene as potential carcerands. ii iii Table of Contents Chapter Pg. 1. Introduction 1 Corannulene…………………………………………………………. 8 Synthesis of corannulene…………………………………………….. 12 References…………………………………………………………… 20 2. Understanding Conjugation through Diethynylcorannulene series – Synthesis, Structure & Properties 23 Synthesis of 1,8 & 1,5-diethynylcorannulene…………………………. 24 (4-bromophenyl)corannulene acetylene synthesis (15) ……………...... 28 Synthesis……………………………………………………………... 30 Purity of Iodocorannulene (18) …………………………………... 34 Purity of diethynylcorannulene (16 & 17) ………………………… 35 Results & Discussion………………………………………………... 38 Conclusions…………………………………………………………. 51 References…………………………………………………………… 53 3. Importance of Linker: Synthesis, Structure & Properties 54 Synthesis…………………………………………………………….. 55 [(3Z)-4-chloro-3-buten-1-yn-1-yl)]corannulene synthesis (34)……….. 57 Results & Discussion………………………………………………... 61 iv Conclusions………………………………………………………….. 71 References…………………………………………………………… 72 4. Corannulene Based Carcerands – Synthesis, Structure & Properties 73 Synthesis……………………………………………………………... 75 Results & Discussion………………………………………………... 83 Conclusions…………………………………………………………. 91 References…………………………………………………………… 93 5. Experimental Details 95 6. Spectra 124 v Acknowledgement My graduate school would certainly be incomplete without acknowledging the guidance, support of several people. First and foremost I would like to thank God for bestowing his kindness upon me and providing me the strength and courage to overcome obstacles in life. I certainly extend my deepest and utmost thanks to my dear wife Mallika for her constant support, patience and endless motivation in the most needed times of my Ph.D career. Words are certainly sparse to explain the constant support and helpful guidance by my research advisor Dr. James Mack. His strong passion and renewed excitement to explore has been the key to succeed in my career. He takes utmost care in molding a student as a whole and not just the academic aspects. I would like to extend my sincere thanks to my committee members Dr. Bruce Ault and Dr. David Smithrud in helping me approach the problem in completely different perspective. Further, I would like to acknowledge Dr. Necati Kaval (photochemistry/laser experiments), Dr. Jeanette Krause (crystallography) and Dr. Stephan Macha (MALDI experiments) for their helpful support in obtaining critical information to support my research. vi I would also like to thank Mack group members for their continued support. Also, I would like to thank Department of Chemistry, University of Cincinnati for their financial support as to perform my research. I would also like to thank my parents and sisters for their continued support in my highs and lows. vii List of Figures Figure Pg. Figure 1: OLED products and its increasing application…………………………….. 2 Figure 2: Stability & Importance of blue color……………………………………….. 3 Figure 3: Transition based on MO theory…………………………………………….. 4 Figure 4: Band-gap comparison of different π-conjugated system……………………... 5 Figure 5: Poly(p-phenylene-vinylene)…………………………………………………. 5 Figure 6: UV-Vis spectra of fullerene and difullerenylacetylene………………………. 6 Figure 7: Structural and chemical similarities of (1) with fullerene [C60] & benzene….. 7 Figure 8: Front & side view of bowl shaped corannulene (top left & bottom), Electron density map (top right) of corannulene (1)…………………………………... 9 Figure 9: Comparison study of multiethynylphenyl derivatives of (1)………………… 19 Figure 10: Target compounds to test conjugation with different chromophores……... 23 Figure 11: Two novel disubstiution patterns: 1,8 (16) & 1,5 (17) diethynylcorannulene. 24 Figure 12: Mechanistic pathway of Sonogashira coupling reaction……………………. 33 Figure 13: Absorption spectra of 1,8/1,5-diethynylcorannulene series………………... 39 Figure 14: Absorption spectra of 24, 25, and 26……………………………………… 40 Figure 15: Absorption from multiethynyl substituted corannulene (28 and 29)………. 42 Figure 16: B3LYP/6-31G* optimized structures of 20, 21, 22, 23, 24, and 25………... 43 Figure 17: HOMO to LUMO and HOMO-1 to LUMO+1 transition for 20, 21, 22 and 23…………..………………………………………………………… 44 Figure 18: HOMO to LUMO and HOMO-1 to LUMO transitions for 24 and 25…… 45 Figure 19: Fluorescence spectra with excitation at 300 nm…………………………… 46 viii Figure 20: Fluorescence spectra (excitation at 400 nm)………………………………. 47 Figure 21: Excitation of 16 & 17 at different wavelengths based on its zero order emission………………………………………………………………….. 48 Figure 22: Excitation of 20 and 21 at different wavelengths based on its zero order emission data……………………………………………………………. 48 Figure 23: Laser excitation at 325 nm………………………………………………… 49 Figure 24: Fluorescence spectra of anthrancene along with laser excitation at 405 nm... 50 Figure 25: Laser excitation at 325 & 405 nm…………………………………………. 50 Figure 26: Surprising similarity in absorption for 20 and 31…………………………... 55 Figure 27: Influence of linker over absorption of corannulene based compounds……. 62 Figure 28: Influence of linker length on absorption of 22, 23 vs. 38, 43……………… 63 Figure 29: Influence of linker length on absorption of tetrasubstitued corannulene derivatives…………………………………………………………………. 64 Figure 30: B3LYP/6-31G* optimized structures of compound 38, 43, 44 and 47……... 65 Figure 31: B3LYP/6-31G* calculated orbital transitions for compounds 38, 39 and 43 66 Figure 32: Interaction of corannulene’s core orbitals with substituents………………. 68 Figure 33: Fluorescence of compounds with enediyne linker with emission at 300 nm.. 69 Figure 34: Laser excitation at 325, 405 and 442 nm…………………………………... 70 Figure 35: Metal complexes of different types……………………………………….. 73 Figure 36: Open [6,6] 1,5-corannulene cyclophane and [6,6] 1,8-corannulene cyclophane……………………………………………………………….. 74 Figure 37: Closed [2,2] 1,5-corannulene cyclophane and [2,2] 1,8-corannulene cyclophane……………………………………………………………….. 75 Figure 38: Synthesis of corannulene trimer held by enediyne bridges (49)……………. 80 Figure 39: Absorption spectra for compounds 31, 49, 55 and its comparison with 1, ix 16 and 17…………………………………………………………………. 85 Figure 40: B3LYP-6-31G* geometry optimized structures of 31, 49 and 55………….. 86 Figure 41: B3LYP, 6-31G* calculated orbital transitions of 31, 49 and 55……………. 87 Figure 42: Fluorescence spectra for 31……………………………………………….. 89 Figure 43: Fluorescence spectra of 55……………………………………………….. 90 Figure 44: Fluorescence spectra with laser excitation for compound 49……………… 90 x List of Schemes Scheme Pg. Scheme 1: First synthesis of corannulene (1) by Barth & Lawton in 1966……………… 9 Scheme 2: Three step synthesis of corannulene using FVP……………………………. 10 Scheme 3: Second solution phase synthesis of corannulene (1) in 1996……………….. 10 Scheme 4: Semibuckministerfullerene synthesis……………………………………….. 11 Scheme 5: Importance of octabromofluoranthene towards synthesis of corannulene…. 11 Scheme 6: Large scale synthesis of corannulene (1)…………………………………… 12 Scheme 7: Total synthesis of Corannulene……………………………………………. 13 Scheme 8: Derivatives of Corannulene (1)…………………………………………….. 15 Scheme 9: Multiethynyl derivatives of corannulene (1)………………………………… 17 Scheme 10: Synthesis of 1,8-dialkyncorannulene (16)…………………………………. 25 Scheme 11: Different approach towards synthesis of 15 ……………………………… 29 Scheme 12: Synthesis
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