This thesis presents the synthesis, characterization, and device performance of a
series of cyclopentadithiophene (CPDT)-naphthalene (NDI) donor-acceptor (D-A)
ABA-type oligomers and copolymers. These oligomers composed of
CPDT-NDI-CPDT unit with various alkyl chains are successfully synthesized via
direct arylation using palladium complex catalyst. The corresponding copolymers are
synthesized by oxidative polymerization using FeCl3. All of oligomers and
copolymers are systematically characterized and analyzed by gel permeation
chromatography (GPC), 1H NMR and UV-vis-NIR absorption spectroscopies, cyclic
voltammetry (CV), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and
differential scanning calorimetry (DSC). GPC measurement shows that these
polymers are of relatively high molecular weight, Mn = 21800-76000. These
copolymers show deep-red absorption including near-infrared region (up to 1100 nm)
due to their quite narrow bandgap. Impressively, the electrochemical property of the
resulting copolymers exhibits lowest unoccupied molecular orbital (LUMO) at about -
3.7 eV, which has been considered as the favorable level as n-type materials for use in
organic photovoltaic devices (OPVs).
These copolymers exhibit only n-type property giving the highest electron
mobility of 3.7 x 10-4 cm2 V-1 s-1 in organic field-effect transistor because of its strong
intermolecular interaction. On the other hand, the copolymer with highly soluble
branched alkyl chain shows the highest power conversion efficiency of 0.25% in
organic photovoltaic device.
To investigate the versatile reactivity of C-H direct arylation, the copolymers
composed of above unit with benzothiadiazole, thiophene, or bithiophene are also
II
synthesized by direct arylation polymerization. All polymers have higher molecular
weight (Mn = 18000-52000) than the alternative polymers of dibromo-NDI and CPDT
obtained from similar reaction condition. The optical and electrochemical properties
of these polymers are measured by UV-vis-NIR spectra, 1H-NMR, GPC and CVs.

Table of content
Abstract I
Table of content III
Chapter 1. Introduction and purpose 1
1.1 Introduction 1
1.2 Organic semiconductors 1
1.3 Charge transport in organic semiconductors 4
1.3.1 P-type organic semiconductors 5
1.3.2 Ambipolar semiconductors 9
1.4 Application of conjugated polymers 11
1.4.1 Organic field effect transistors 11
1.4.2 Organic photovoltaics 16
1.5 Structure and property of conjugated polymers 20
1.6 Synthesis of conjugated polymers 25
1.7 Aim of this work 33
Chapter 2. Synthesis and Characterization of ABA Type Copolymers Comprising of Cyclopentadithiophene and Naphthalenediimide 34
2.1 Introduction 34
2.2 Synthesis 38
2.2.1 Synthesis of monomers 38
2.2.2 Synthesis of polymers 51
2.3 Optical and electrochemical properties 54
2.4 Thermal properties 65
2.6 Device characteristics of organic field effect transistors and organic photovoltaics 66
Chapter 3. Synthesis and Characterization of AB alternative copolymers by C-H direct arylation 74
3.1 Introduction 74
3.2 Synthesis of polymers 75
3.3 Optical and electrochemical properties 79
Chapter 4. Conclusions and Outlook 85
Chapter 5: Experimental section 87
5.1 General Procedures 87
5.2 Synthesis of cyclopentadithiophene (CPDT) 88
5.2.1 Bis(2-iodothiophen-3-yl) methanol (1) 88
5.2.2 Bis(2-iodothiophen-3-yl)methanone (2) 89
5.2.3 Cyclopenta[2,1-b;3,4-b']dithiophen-4-one (3) 89
5.2.4 4H-Cyclopenta[2,1-b;3,4-b']dithiophene (4) 90
5.2.5 4,4-bis(n-hexadecyl)cyclopenta[2,1-b;3,4-b']dithiophene (5a) 90
5.2.6 4,4-bis(2-ethylhexyl)cyclopenta[2,1-b;3,4-b']dithiophene (5b) 91
5.3 Synthesis of Naphthalenediimide (NDI) 93
5.3.1 2,6-Dibromonaphthalene-1,4,5,8-tetracarboxydianhydride (6) 93
5.3.2 N,N’-bis(n-hexadecyl)-2,6-dibromo-1,4,5,8-naphthalene diimide (7a) 94
5.3.3 N,N’-bis(2-ethylhexyl)-2,6-dibromo-1,4,5,8-naphthalene diimide (7b) 95
5.4 Synthesis of monomers 96
5.4.1 CPDT-NDI-CPDT 96
5.5 Synthesis of polymers 100
5.5.1 P(CPDT-NDI-CPDT) 100
5.5.2 P(CPDT-NDI-CPDT-BT) 102
Reference 105
Appendix 112

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