Novel Organic Optoelectronic Materials Based On Electron-Deficient Fused Heterocycle Building Blocks

Organic optoelectronic materials are the significant material foundation for organic thin-film transistors(OTFTs) and organic solar cells(OSCs). They are also the research objects in update themes for investigating the relationship between molecular structures and material properties. Accordingly, design and synthesis of new organic optoelectronic materials is of great significance. The study on organic optoelectronic materials containing electron-deficient fused heterocycle building blocks is among the key issues. This thesis focuses on the design and synthesis of organic molecules and polymers with a π-conjugated electron-deficient fused heterocycle backbone, and investigating the relationship between molecular structures and photoelectric properties. The works are divided as follows:Chapter one introduces the relevant physical basics necessary to understand the general processes in OTFTs and OSCs and to characterize them. The comprehensive overview of n-type organic semiconductors in OTFTs and conjugated polymer donor materials in OSCs are given, followed by the description of the aim and main contents of this thesis.Chapter two describes a series of novel naphthoylene(trifluoromethyl-benzimidazole)-dicarboxylic acid imides(compound 3a, 3b, 4a and 4b). These materials combine an enlarged planar π-conjugated naphthalene diimide(NDI) core with strong electron-withdrawing trifluoromethyl substitution for reducing their lowest unoccupied molecular orbital(LUMO) energy levels. The synthesis, optical and electrochemical investigations are reported and discussed. The OTFTs based on these materials showed typical n-type OTFTs behavior and compound 3a achieved an electron mobility as high as 0.10 cm2V-1s-1.Chapter three deals with the synthesis of two new conjugated polymers based on trifluoromethylated thieno[3,4-b]thiophene-2-ethyl carboxylate(PBDT-TTCF3 and PPDA-TTCF3). Trifluoromethylation reduces frontier molecular orbitals(FMO) energy levels of new conjugated polymers compared with their non-trifluoromethylated counterparts. Although trifluoromethyl group on the 3-position of thieno[3,4-b]thiophene can result in a significant twist of the conjugated main-chains from planarity and thus disrupt the effective conjugation in polymers with aryl repeating units, this steric hindrance can be relieved by using an alkynyl linker. Solar cell devices with PPDA-TTCF3 as a donor and PCBM as an acceptor have achieved a signicantly improved open-circuit voltage of 0.93 eV.Chapter four is based on a series of random copolymers(PR-TiI, PR-2TiI and PR-TVTiI) containing electron-deficient thieno[3,4-c]pyrrole-4,6-dione(TPD) and isoindigo(iI) building blocks. By varying the electron-rich building blocks, the resulting random copolymers with well adapted optical and electronic properties were generated. These copolymers all exhibit broad absorption and appropriate frontier molecular orbitals(FMO) energy levels. The solar cells devices based on copolymer PR-TiI as a donor and PCBM as an acceptor show a preliminary power conversion efficiency of 1.75%.Chapter five gives details on the synthesis of novel benzodipyrrolidone-based monomers and conjugated polymers. The study is based on comparison of N-alkylated and N-acylated π-conjugated systems containing electron-deficient benzodipyrrolidone building blocks. N-acylated materials have displayed significantly reduced the LUMO energy levels(about 0.3 eV) and improved reversibility of reductive doping compared with their N-alkylated counterparts. The benzodipyrrolidone-based polymers show typical n-type characteristics. The OTFT devices based on N-acylated P6 thin films have exhibited an electron mobility of 0.012 cm V-1s-1. Significantly, N-acylation may apply in other conjugated materials with lactam repeating units.Chapter six summarizes the thesis and outlines ideas for future work.