Synthesis And Properties Of D-A Polymers Based On Benzodithiophene

Conjugated polymers have persistently attracted attention owing to their wide application in organic photoelectric materials. D-A polymers containing electron donor and electron acceptor units in the main chains have excellent photophysical properties as well as the carrier transport properties. So conjugated polymers have become a hot research topic in OLEDs, solar cell materials and chemical/biological sensors.The research of this thesis was based on benzo[1,2-b:4,5-b’]dithiophene(BDT) with a highly conjugated plane. Terpyridine, with a extensive transition metal coordination ability, was used to modify benzodithiophene. D-A supramolecular polymers were formed by self-assembly of transition metal coordination. At the same time, two novel D-A polymers with narrow energy gaps were obtained via copolymerizing of benzodithiophene and highly conjugated strong electron acceptor benzodipyrrolidone. All synthesized monomers and polymers were characterized in detail, and their properties were studied systematically.(1) Synthesis and properties of D-A molecules of terpyridine-modified benzodithiophene. 2,2’:6’,2"-terpyridine was used to modified benzodithiophene in order to form molecular M1 and M2 containing the A-D-A electronic structure and bis-terpyridine units. Studies indicated that the molecular plane-conjugated degree and the intermolecular π-π stacking interactions had a great influence on the intramolecular charge transfer. The UV-Vis absorption peak of M2 had a redshift of 24 nm, reaching to 476 nm, and the fluorescence emission peak of M2 had a redshift of 32 nm, reaching to 553 nm compared with M1. The electrochemical energy gaps of M1 and M2 were 1.26 eV and 1.49 eV, respectively. The thermal decomposition temperatures were 335 ℃ and 430 ℃, respectively.(2) Synthesis and properties of D-A supramolecular polymers based on benzodithiophene. Alkoxy and thienyl groups were used to modify benzodithiophene, forming different units containing electron donating ability and molecular configuration. Then they formed A-D-A structure of supramolecular building units BDT-OR and BDT-Th, coupled with 2,2’:6’,2"-terpyridine. At last, metallo-supramolecular polymers P-BDT-OR and P-BDT-Th were synthesized under the induction of Ru2+. Studies indicated that owing to the existence of metal-ligand charge transfer, the D-A structures of the metallo-supramolecular polymers P-BDT-OR and P-BDT-Th were enhanced, intramolecular charge transfer abilities were increased, the UV-Vis absorption spectrums were red shifted, and energy gaps were reduced. UV-Vis absorption peaks of the supramolecular polymers, P-BDT-OR and P-BDT-Th, were 521 nm and 522 nm, respectively. Electrochemical energy gaps were 1.86 eV and 1.78 eV, respectively. The thermal decomposition temperatures were 300 ℃ and 389 ℃, respectively.(3) Synthesis and properties of D-A polymers consists of benzodithiophene and benzodipyrrolidone. Benzodithiophene modified by alkoxy or thienyl group was copolymerized with acceptor unit — highly-conjugated benzodipyrrolidone. Then polymers P1 and P2 were formed and their UV-Vis absorption properties, electrochemical properties and thermal stability were investigated. Research showed that UV-vis absorption peaks of P1 and P2 were 619 nm and 620 nm, respectively. Owing to the enhancement of the D-A structure after copolymerization, compared with monomer BDP, obvious redshift were occured. The electrochemical energy gaps of P1 and P2 were 1.57 eV and 1.51 eV, respectively. The thermal decomposition temperatures were 319℃ and 408℃, respectively.