A poly(alkylsulfany)thiophene functionalized with carboxylic groups

Different routes, based on the Stille coupling, to the obtainment of a polythiophene bearing a carboxyhexylsulfanyl chain every two thiophene rings (PTCOOH) are here reported and discussed. Two PTCOOHs with different chain lengths were obtained: the shorter by hydrolysis of a polymeric ester precursor and the longer by direct Stille coupling from suitable monomers. They possess similar electrochemical properties but behave differently when aggregation and fluorescence are concerned. The PTCOOH obtained by hydrolysis is found to be fluorescent in a good solvent such as THF, and its fluorescence quantum yield decreases as the extent of aggregation increases. The polymer obtained by direct Stille coupling is less fluorescent, consistently with its proneness to aggregate. The PTCOOH obtained by hydrolysis is therefore more promising in view of the build-up of solid-state devices with exploitable fluorescence properties.