SPECTROSCOPIC PROPERTIES OF POLY(3-ALKYLTHIOPHENES) AND THEIR HEAD-TO-HEAD, TAIL-TO-TAIL COUPLED ANALOGS POLY(4,4'-DIALKYL-2,2'-BITHIOPHENES)

Electrochemical doping of new soluble conducting polymers, namely, poly(4,4'-dialkyl-2,2'-bithiophenes), has been studied 'in situ' and 'ex situ' by various spectroscopic methods. These compounds represent the 'head-to-head' and 'tail-to-tail' analogues of poly(3-alkylthiophenes). The pi-->pi* transition in poly(4,4'-dialkyl-2,2'-bithiophenes) is blue shifted with respect to that characteristic of poly(3-alkylthiophenes) suggesting a higher torsion angle between the adjacent substituted thiophene rings. The doping-induced bipolaronic bands (Vis-NIR) are, however, located in essentially the same positions as the doping-induced ones in poly(3-alkylthiophenes). This observation may suggest that during doping, more twisted poly(4,4'-dialky1-2,2'-bithiophenes) adopt a structure more similar to that of doped poly(3-alkylthiophenes). The changes in FT-IR spectra are also consistent with the bipolaron model since all the five expected doping-induced modes appear with the onset of the oxidation peak and grow in intensity with increasing potential.