Synthesis and characterization of regioregular polymers containing substituted thienylene/bithienylene and phenylene repeating units

Abstract

Regioregular polymers poly(3-alkyl-2,5-thienylene-alt-1,4-phenylene) (PBTCn, n = 4, 8, 12) and poly[1,4-bis(3-alkyl-2-thienyl)phenylene] (PBTBCn, n = 4, 8, 12), which contain alternating phenylene and substituted thienylene or bithienylene repeating units, have been chemically and/or electrochemically synthesized and characterized. Their structures are consistent with that expected as indicated by NMR, FTIR, and microanalysis. The change in glass transition temperature and UV-vis and fluorescence spectra with modification of polymer backbone and increase of the alkyl chain length has been observed and discussed. The PBTCn, series shows better thermal stability in air, and the compounds in the series are partially crystalline. The PBTCn, polymers have liquid crystalline properties as shown by MDSC, XRD, and polarized optical microscopy. XPS study performed on both the neutral and doped states shows the formation of charge carrier in the polymer backbone when doped. The polymers are both p- and n-dopable as indicated by cyclic voltammetry. Electrochromism when the polymers are p-doped is also evidenced by the spectral changes in UV-vis-NIR region.