Theoretical Study On The Structures And Properties Of Conjugated Polymers And Molecular Design Of Organic Conductive Materials And Organic Solar Cell Materials

In this thesis, conjugated polymers, which are extremely attractive materials, are studied by density functional theory (DFT). We calculated the structures of monomer, oligomer and polymer, and then discussed the potential as organic conductive materials and organic solar cell materials. In addition, we also analyzed the effect of different donor-acceptor ratios on the results. The main content of this thesis as follows:In chapter 1, we introduced the research progress, the conductive mechanism and the design principles of the organic conducting polymer, which attract much attention due to the perfect electric property and extraordinary optical property. Then we also introduced the development and work principles of organic solar cell. In addition, the work we did and its significance are summarized.In chapter 2, a thorough introduction to the computation methods-Density Function Theory was included. In addition, we also introduced several analysis methods and theoretical measures, including atoms in molecular (AIM) theory, nature bond orbital (NBO), Nucleus-independent chemical shifts (NICS) and time-dependent density functional theory(TD-DFT).In chapter 3, The structures and properties of dibenzo[b,d]thiophene (DBT) based alternating donor-acceptor conjugated oligomers, in which thieno[3,4-b]pyrazine (TP), thieno[3,4-b]thiadiazole (TD), and [1,2,5]thiadiazolo[3,4-e]thieno[3,4-b]pyrazine (TTP) as acceptors, and their periodic polymers were investigated by the density function theory (DFT) at the B3LYP/6-31G(d) level. The bond length, electron density at bond critical points (BCPs) and nucleus-independent chemical shift (NICS) are analyzed and correlated with the conductive properties. NICS shows that the conjugation degree is increased with main chain extension. Research results show the conductive ability of compounds with 1:2 D-A ratio is better than that with 1:1 D-A ratio. The reorganization energies and energy bands also are considered. The results suggest that (BTDDBT)n and (BTPDDBT)n have small reorganization energy (0.163 and 0.152 eV, respectively) and quite low energy gap (0.73 and 0.56 eV, respectively), which indicate that they may be potential organic conductive materials.In chapter 4, A series of novel co-polymers which are obtained by combining 3,4-vinylenedioxythiophene(VDOT) with thieno[3,4-b]pyrazine(TP), furo[3,4-b]pyrazine(FP) and 6H-Pyrrolo[3,4-b]pyrazine(PP) are prepared. The structures and electronic properties of those polymers as well as their corresponding monomers and oligomers are studied by the density function theory (DFT) at B3LYP level with 6-31(G). The change of the bond lengths, bond critical point (BCP) properties, Wiberg bond index (WBIs) and nucleus-independent chemical shift (NICS) show that the conjugational degree is increased with main chain extension. To understand the effect of the ratio of VDOT to TP, FP and PP unit (V-P ratio) for electronic properties of investigated compounds, those compounds with the V-P ratio of 1:1,1:2 and 2:1 are analyzed. The results show that the conjugational degree of oligomers with 1:2 V-P ratio is the best and that of oligomers with 2:1 V-P ratio is the worst. The small electron-transfer reorganization energy indicates polymers with 1:2 and 2:1 V-P ratio may be potential electron transport materials. The band structure analysis shows that all of polymers with 1:1 V-P ratio which include (VDOT-TP)n, (VDOT-FP)n and (VDOT-TP)n have relatively narrow band gap and very large bandwidth. Therefore, those polymers can be considered as potential organic conductive materials. In addition, (VDOT-BTP)n and (VDOT-BFP)n have quite low band gap (0.73 and 0.87 eV, respectively) and suitable bandwidth which indicate that they may be good intrinsic conductors.In chapter 5, we designed nine new copolymers as donors for organic solar sells. Those polymers were based on benzo[2,1-b;3,4-b’]dithiophene (BDP) as donor and 2,1,3-benzothiadiazole(BT) as acceptor, and then incorporated thiophene, furofuran and pyrrole with ratios of 1:1 and 1:2. The abilities of stabilities in the environment, absorbing sunlight, and photovoltaic properties have been analyzed. The results showed that when BDPBT was combined with thiophene, furofuran and pyrrole, the abilities of exciton generation and dissociation were enhanced, the absorption peaks exhibited red shift in their absorption spectrums, the hole transfer (λh) and electron transfer (λe) reorganization energy reduced. Especially, (BDTBT-T2)n, which had relatively high open-circuit voltage compared with other eight polymers when PC61BM acted as an acceptor, indicated that it was a champion material for donors in bulk-heterojunction solar cell.