Temperature Depenndence of the Doping Effect of Poly(3-alkylthiophene) and Polaronic State

Abstract

The absorption spectrum of poly(3-alkylthiophene) such as poly(3-docosylthiophene) changes at the solid-liquid phase transition. This phenomenon can be interpreted in terms of the change of the effective conjugation length due to the existence of some twisted bonds between neighbouring thiophene rings on the polymer main chain in the liquid state. From measurements of the cyclic voltammogram in solid and liquid phases, the top of the valence band is confirmed to be located at a higher energy in the liquid state. Formation of polaronic states, even in the liquid state, has been clarified from the drastic change of absorption spectrum upon doping. A simple energy band scheme of poly(3-alkylthiophene) in the solid and liquid states is indicated.