Electronic Properties of Poly[3-(1,1-dimethylpropyl)thiophene] and Poly(3-cyclohexylthiophene)

Poly(3-alkylthiophene) (P3AT) with alkyl side chains longer than or equal to butyl is soluble in some solvents and fusible. However, conductive states of P3AT are unstable. In order to develop soluble conductive polymers with a stable conductive state, electronic properties of poly[3-(1,1-dimethylpropyl)thiophene] (P3DMPT) and poly(3-cyclohexylthiophene) (P3cHT) were compared with those of poly(3-octylthiophene) (P3OT). The photoabsorption spectrum of P3DMPT did not change before and after doping with NOBF4. This is due to its high oxidation potential. The oxidation peak in the cyclic voltammogram of P3DMPT was 1.65 V vs. Ag/Ag+, which is too high to be doped with NOBF4. Polaron peaks were observed after the doping of P3cHT. The polarons of P3cHT decayed faster than those of P3OT with time. However, the behavior of the electron spin resonance spectrum of P3cHT was different from that of P3OT: the spin concentration of P3cHT decreased, whereas the spin concentration of P3OT increased with time. The conductive state of P3cHT will decay through different mechanism of P3OT: their dedoping will be a reverse process of doping. The reverse dedoping processes of P3cHT will be due to the high oxidation potentials of P3cHT.