| Abstract
| - A series of polymers comprising alternating phenylene and thienylene repeating units andwith electron-donating or -withdrawing groups attached on thienylene units, i.e., poly[1,4-bis(3-X-2,5-thienylene)phenylene-alt-2,5-dioctyl-1,4-phenylene] (PBTX, X = OMe, H, Cl, Br, CN), has been synthesizedand characterized. These polymers are highly fluorescent, among which PBTH shows the highest solutionquantum yield, up to 94% relative to quinine sulfate. The absorption and emission peak wavelengths ofPBTOMe are bathochromically shifted and band gap (Eg) is lowered by the presence of electron-donatingOMe group, in comparison with PBTH. The influence of electron-withdrawing groups, Br, Cl, and CN,on the absorption peak wavelength and Eg, on the other hand, is not so great. Nevertheless, the film ofPBTCN shows an emission maximum near to that of PBTOMe due to the strong interchain interactions.The band 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 ofPBTH. The electronic structures of PBTBr and PBTCl change slightly in comparison with PBTH, butboth the IP and EA of PBTCN are greatly increased (by 0.5 eV), leading to an unchanged Eg. The changesin electronic structure make PBTOMe a suitable candidate as an active layer in LED device, as it shouldfavor a balanced electron and hole injection, despite its moderate quantum yield. PBTCN can be used asan excellent ETL material in multilayer devices as its EA is even higher than that of CN−PPV. Thepolymers are dopable by FeCl3 and I2 except for PBTCN, in agreement with electrochemical results. PBTHshows a good conductivity up to 4 S cm-1 when doped by FeCl3. The doped samples are examined usingXPS and the formation of charge-transfer complex is suggested. The oxidization of both the S and Oatoms in FeCl3-doped PBTOMe is also supported by XPS.
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