Thiophene-containing organic semiconducting heteroacenes for electronic applications [Elektronische Ressource] / Peng Gao

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Thiophene-Containing Organic Semiconducting Heteroacenes for Electronic Applications Dissertation zur Erlangung des Grades ‘Doktor der Naturwissenschaften’ am Fachbereich Chemie und Pharmazie der Johannes Gutenberg-Universität in Mainz Peng Gao Geboren in Shanxi Province / China Mainz 2009 Dekan: 1. Berichterstatter: 2. Berichterstatter: Tag der mündlichen Prüfung: 17, Feb. 2010 Dedicated to my family Table of Contents List of Figures ······················································································································ vi List of Schemes ··················································································································· xv List of Tables ···················································································································· xvii Glossary of Abbreviations ···························································································· xviii Chapter 1 Introduction and Motivation ············································································· 1 1.1 Semiconducting materials for organic field-effect transistors (OFETs) ············· 1 1.1.1 Oligoacenes vs. conjugated polymers ........................................................... 4 1.1.2 PAH acenes and heteroacenes .........................................................

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Thiophene-Containing Organic
Semiconducting Heteroacenes for
Electronic Applications


Dissertation





zur Erlangung des Grades
‘Doktor der Naturwissenschaften’

am Fachbereich Chemie und Pharmazie der
Johannes Gutenberg-Universität in Mainz



Peng Gao
Geboren in Shanxi Province / China
Mainz 2009



































Dekan:
1. Berichterstatter:
2. Berichterstatter:
Tag der mündlichen Prüfung: 17, Feb. 2010






Dedicated to my family
Table of Contents
List of Figures ······················································································································ vi
List of Schemes ··················································································································· xv
List of Tables ···················································································································· xvii
Glossary of Abbreviations ···························································································· xviii
Chapter 1 Introduction and Motivation ············································································· 1
1.1 Semiconducting materials for organic field-effect transistors (OFETs) ············· 1
1.1.1 Oligoacenes vs. conjugated polymers ........................................................... 4
1.1.2 PAH acenes and heteroacenes ........................................................................ 5
1.1.2.1 Why heteroacenes? ·················································································· 5
1.1.2.2 p-Channel heteroacenes ··········································································· 7
1.1.2.3 n-Channel heteroacenes8
1.2 Design principles of high performance oligoacenes ············································ 9
1.2.1 Energy levels of organic semiconductors ...................................................... 9
1.2.2 Tuning the HOMO level of p-channel oligoacenes .................................... 11
1.2.3 Tuning the LUMO level of n12
1.3 A summary of synthetic methods toward thiophene containing heteroacenes
········································································································································ 13
1.3.1 Synthesis of thiophene containing heteroacenes by sulfur-bridge
formation ................................................................................................................... 14
1.3.1.1 Formation of sulfur-bridges by triflic acid induced electrophilic
substitution ········································································································ 14
1.3.1.2 Introducation of thiophene rings by aromatic nucleophilic substitution
(S Ar) reaction ·································································································· 17 N
1.3.1.3 Introduction of thiophene rings by electrophilic cyclization reaction ···· 19
1.3.1.4 Intro thiophene ring by Hinsburg thiophene synthesis ··········· 20
1.3.2 Synthesis of thiophene containing heteroacenes by direct annulation of
thiophene units ........................................................................................................ 21
1.3.2.1 Friedel-Crafts-type alkylation and acylation reactions ·························· 21
i 1.3.2.2 Cadogan reductive cyclization on thiophene units ································· 23
1.4 Solid-state structure of full ladder oligoacenes ··················································· 24
1.5 Solution processed organic thin film field-effect transistors ····························· 26
1.5.1 Solution processing techniques .................................................................... 26
1.5.2 Basic operation ............................................................................................... 28
1.6 Motivation for the present work ··········································································· 29
1.6.1 Development of novel pentacene analogues: the sulfur approach ......... 29
1.6.1.1 What benefit can sulfur substitution bring to us? ··································· 29
1.6.1.2 Extended π-systems in conjugated oligomers for molecular
electronics-the longer, the better? ······································································ 31
1.6.2 Our approach toward design and synthesis of new thiophene fused
heteroacenes ............................................................................................................. 34
1.7 References ················································································································ 36
Chapter 2 Conjugated Sulfur Containing Heteropentacene Analogues for p-Channel
Organic Field-effect Transistors (OFETs) ········································································· 43
2.1 Introduction ············································································································ 43
2.2 Synthesis and characterization of benzo[1,2-b:4,5-b’]bis[b]benzo-thiophene
(BBBT) as pentacene analogues ·················································································· 45
2.2.1 Synthesis of benzo[1,2-b:4,5-b’]bis[b]benzothiophene (BBBT) derivatives
.................................................................................................................................... 45
2.2.2 Solid-state crystal structure and packing ................................................... 47
2.2.3 Powder X-ray diffraction (PXRD) analyses of BBBT films ....................... 50
2.2.4 Photophysical properties .............................................................................. 52
2.2.5 Electrochemical properties ........................................................................... 53
2.2.6 OFETs device fabrication based on BBBT derivatives .............................. 55
2.3 Synthesis and characterization of dithieno[2,3-d;2’,3’-d’]benzo[1,2-b;4,5-b’]di-
thphene (DTBDT) as pentacene analogues ······························································· 58
2.3.1 Synthesis of dithieno[2,3-d;2’,3’-d’]benzo[1,2-b;4,5-b’]dithiophene
(DTBDT) derivatives ............................................................................................... 58
2.3.2 Solid-state crystal structure and packing ................................................... 60
ii 2.3.3 Powder X-ray diffraction (PXRD) analyses of DTBDT films ................... 63
2.3.4 Photophysical properties ............................................................................... 65
2.3.5 Electrochemical properties ............................................................................ 67
2.3.6 OFET device fabrication based on DTBDT derivatives ............................ 68
2.3.6.1 Application of 2b for the semiconducting channels in OFETs from
solution ············································································································· 68
2.3.6.2 Device fabrication of 2c by controlled dip-coating technique ··············· 72
2.4 Electronic structure computation ········································································· 75
2.5 Conclusion ·············································································································· 79
2.6 References ··············································································································· 80
Chapter 3 Sulfur and Nitrogen-bridged Heteroheptacenes and Their Application for
p-Channel Organic Thin Film Transistors ········································································ 84
3.1 Introduction ············································································································ 84
3.1.1 Ladder-type heteroheptacenes ..................................................................... 85
3.1.2 Reactivity of carbazole under the condition of electrophilic substitution
reaction ...................................................................................................................... 86
3.1.3 How to solve the problem when carbazole was used as the nucleophilic
core to construct the new molecules? ................................................................... 88
3.2 Synthesis and characterization of sulfur and nitrogen-bridged heptacenes
with carbazole (Cz) as the central π system ······························································ 89
3.2.1 Synthesis of dibenzo[b,b']thieno[2,3-f:5,4-f']-carbazole (DBTCz) deriva-
tives ............................................................................................................................ 89
3.2.2 Synthesis of bisthieno[3,2-b]thieno[2,3-f:5,4-f']-carbazoles (BTTCz) ....... 93
3.2.3 Synthesis of diindolo[3,2-b:2',3'-h]benzo[1,2-b:4,5-b']bis[1]benzothio-
phene (DIBBBT) ....................................................................................................... 94
13.2.4 Structure proof of the heteroacenes by H NMR spectroscopy ............... 95
3.2.5 Solid-state crystal structure and packing properties revealing the alkyl
substituting effect on the solid structure .............................................................. 96
3.2.6 Powder X-ray diffraction (PXRD) analyses and film microstructure for
compounds DBTCz and BTTCz .......................................................................... 105
iii 3.2.7 Scanning electron microscopy (SEM): morphological characterization of
compounds DBTCz and BTTCz .......................................................................... 108
3.2.8 Photophysical properties ............................................................................. 110
3.2.9 Electrochemical properties113
3.2.10 OFET fabrication based on DBTCz derivatives ...................................... 115
3.3 Conclusion ············································································································· 1 19
3.4 References ·············································································································· 120
Chapter 4 Study of Structure-Property Relationship of Sulfur and (or) Nitrogen-
Bridged Heptacenes ·········································································································· 122
4.1 Introduction122
4.1.1 New electronically active organic molecular building blocks ............... 123
4.1.2 Single crystal to single crystal phase transition ....................................... 125
4.1.3 Sulfur-extrusion reaction in dibenzo- or dithieno[l,2]dithiin ................ 127
4.2 Synthesis and characterization of sulfur and (or) nitrogen-bridged heptacenes
with dithienopyrrole (DTP) and cyclopenta[2,1-b: 3,4-b']dithiophene (CPDT) as
the central π system ···································································································· 129
4.2.1 Synthesis of bisbenzo[b,b']thienodithieno[3,2-b:2',3'-d]pyrrole (27) and
bisbenzo[b,b']thienocyclopenta [2,1-b:3,4-b']dithiophene (32) ....................... 129
14.2.2 Structure proof of the heteroacenes by H NMR spectroscopy ............. 131
4.2.3 Solid-state crystal structure and packing of the new heteroheptacenes
and the unexpected single-crystal-to-single-crystal (SCSC) phase transition in
the crystal structure of BBTCPDT ....................................................................... 132
4.2.3.1 Solid-state crystal structure and packing of compound BBTDP ·········· 133
4.2.3.2 Single-crystal-to-single-crystal (SCSC) phase transition in the crystal
structure of compound BBTCPDT ·································································· 134
4.2.3.3 Temperature dependant study of the crystal structures ························· 137
4.2.4 Powder X-ray diffraction (PXRD) analyses and film microstructure for
compounds BBTDP and BBTCPDT .................................................................... 142
4.2.5 Scanning electron microscopy morphological characterization of 143
iv 4.2.6 Photophysical properties ............................................................................. 144
4.2.7 Electrochemical Properties .......................................................................... 147
4.3 Synthesis of thieno[2',3':4,5]thieno[3,2-b]thieno[2'',3'':4',5']thieno[2',3':4,5]
thieno [3,2-f][1]benzothiophene (TTTTTBT) and dibenzo[b,b’] thieno-
[2,3-f:,4-f’]bis[1] benzothiophene (DBTBT) ······························································ 149
4.3.1 Synthesis of thieno[2',3':4,5]thieno[3,2-b]thieno[2'',3'':4',5']thieno[2',3':
4,5]thieno[3,2-f] [1]benzothiophene (TTTTTBT)................................................ 149
4.3.2 Synthesis and characterization of dibenzo[b,b’]thieno[2,3-f:,4-f’]bis[1]-
benzo thiophene (DBTBT) via sulfur-extrusion reaction ................................. 150
4.4 MO calculation and electronic structure of heptacenes by varying the
heteroatoms ················································································································ 153
4.5 Conclusion ············································································································ 157
4.6 References ············································································································· 158
Chapter 5 Summary and Outlook ·················································································· 163
6.1 General procedures ······························································································ 169
6.1.1 Chemicals and solvents ............................................................................... 169
6.1.2 Chromatography .......................................................................................... 169
6.1.3 Inert atmosphere ........................................................................................... 169
6.1.4 Apparatus for analysis ................................................................................. 170
6.1.5 OFET devices ................................................................................................. 172
6.2. Synthetic procedures ·························································································· 174
6.3. Reference ·············································································································· 208
Appendix Single Crystal Structures ··············································································· 209
Acknowledgements ········································································································· 254
List of Publications ·········································································································· 256
Curriculum Vitae ············································································································· 258
v List of Figures
Figure 1.1. Examples of applications (a) radio-frequency ID tags; (b), (c) flexable
electronic papers ····································································································· 2
Figure 1.2. Evolution of OFETs performance with time for various p-channel
(pentacene, rubrene, other small molecules, and polymers) and n-channel
organic semiconductors. (v): vacuum deposition; (s) solution deposition; (sc):
single crystal. A range of mobilities for hydrogenated amorphous silicon
(a-Si:H) is shown as reference. ·············································································· 2
Figure 1.3. Classification of organic semiconducting materials in terms of their
structure characteristics and the boxes in orange color showing the train of
thought of this thesis. ····························································································· 3
Figure 1.4. Examples of conjugated polymers for OFETs application ····················· 4
Figure 1.5. Examples of conjugated oligomers for OFETs application ···················· 5
Figure 1.6. Structure of benchmark oligoacenes for organic semiconductors. ······· 6
Figure 1.7. Examples of heteroacenes for organic semiconductors. ························· 6
Figure 1.8. Representative heteroacenes as p-channel OFET materials. ·················· 8
Figure 1.9. nF8
Figure 1.10. Energy levels of organic semiconductors. ············································ 10
Figure 1.11. Empirical rationalization of energy levels of organic semiconductors.
(Left) Range of LUMO levels of typical n-type materials and HOMO levels of
typical p-type materials. (Right) First reduction potential (E ) windows for R1
modified n-type materials with both stable electron conduction and low
doping levels. ········································································································ 11
Figure 1.12. Examples of crystal structures showing the effect of planarization
induced by ring fusion. (a) 5,5’’-diperfluorophenyl-2,2’:5’,2’’:5’’,2’’’-quarter-
thiophene showing inter-ring torsional angles (Reproduced from ref [55].
Copyright 2006 American Chemical Society.); (b)
dibenzo[d,d ′ ]thieno[3,2-b;4,5-b ′]dithiophene showing planar structure.
(Reproduced from ref [37g]. Copyright 2005 American Chemical Society.) · 14
vi Figure 1.13. Herringbone (top) and π-stacking (bottom) arrangements of acenes,
showing HOMO orbital interactions (Spartan ‘04, Wavefunction, Inc.).
(Reproduced from Anthony.) ············································································· 25
Figure 1.14. Schematic presentation of a) drop-casting, b) spin-coating, c)
dipcoating, and d) zone-casting. ········································································ 26
Figure 1.15. Layouts of organic field-effect transistors (OFETs) (left: top-contact;
right: botom-contact) ··························································································· 28
Figure 1.16. Packing diagram of compounds perylo[1,12-b,c,d]thiophene and
fluorinated benzobisbenzothiophene, viewed from the direction showing
[a]inter-molecular contacts. (Reproduced from (a) Sun et al. and (b) Wang et
[b]al. ) ······················································································································· 30
Figure 1.17. Thiophene fused heteroacenes with increasing conjugation and their
band gaps ·············································································································· 33
Figure 1.18. General structure of new thiophene fused heteroacenes ··················· 34
Figure 1.19. Precursors designed for the symmetrically fused thiophene
containing heteroacenes ······················································································ 34
Figure 1.20. Precursor designed for the higher heteroacenes ································· 35
Figure 2.1. Five-ring fused heteroacenes as the pentacene analogues ·················· 44
1Figure 2.2. Expanded aromatic region of H NMR spectra of compounds (a) 1a
(500 MHz, 413 K, d -1,1,2,2-tetrachloroethane); (b) 1b (250 MHz, 300 K, 2
d -dichloromethane). ···························································································· 46 2
Figure 2.3. (a) Pitch angle (P) describing intermolecular slipping along the long
molecular axis (view down short molecular axis). (b) Roll angle (R)
describing intermolecular slipping along the short molecular axis (view
down long molecular axis). (c) Long and short molecular axes of 1. ············· 47
Figure 2.4. Thermal ellipsoid plot of 1a and 1b. The hydrogen atoms are omitted
for clarity. Thermal ellipsoids are drawn at 50% probability. (a) Crystal
stacking of 1a. View down the long molecular axis. (b) View down the b axis
of the stacking molecules of 1a. Dashed line illustrates short contact distance
(ca. 3.5 Å). (c) Crystal packing of 1b. Dashed lines illustrate short
vii