A series of thienylene/phenylene-based polymers functionalized with electron-withdrawing or -donating groups: Synthesis and characterization

A series of polymers comprising alternating phenylene and thienylene repeat ing units and with electron-donating or -withdrawing groups attached on thi enylene units, i.e., poly[1,4-bis(3-X-2,5-thienylene)phenylene-alt-2,5-dioc tyl-1,4 (PBTX, X = OMe, H, Cl, Br, CN), has been synthesized and characteri zed. These polymers are highly fluorescent, among which PBTH shows the high est solution quantum yield, up to 94% relative to quinine sulfate. The abso rption and emission peak wavelengths of PBTOMe are bathochromically shifted and band gap (E-g) is lowered by the presence of electron-donating OMe gro up, in comparison with PBTH. The influence of electron-withdrawing groups, Br, Cl, and CN, on the absorption peak wavelength and E-g, on the other han d, is not so great. Nevertheless, the film of PBTCN shows an emission maxim um near to that of PBTOMe due to the strong interchain interactions. The ba nd structures as deduced from electrochemistry give information supporting the optical measurements. The IP of PBTOMe is decreased but EA is increased , resulting in a lower band gap than that of PBTH. The electronic structure s of PBTBr and PBTCl change slightly in comparison with PBTH, but both the IP and EA of PBTCN are greatly increased (by 0.5 eV), leading to an unchang ed E-g. The changes in electronic structure make PBTOMe a suitable candidat e as an active layer in LED device, as it should favor a balanced electron and hole injection, despite its moderate quantum yield. PBTCN can be used a s an excellent ETL material in multilayer devices as its EA is even higher than that of CN-PPV. The polymers are dopable by FeCl3 and I-2 except for P BTCN, in agreement with electrochemical results. PBTH shows a good conducti vity up to 4 S cm(-1) when doped by FeCl3. The doped samples are examined u sing XPS and the formation of charge-transfer complex is suggested. The oxi dization of both the S and O atoms in FeCl3-doped PBTOMe is also supported by XPS.