An Interpretation on Existence of Thermochromism in Poly-(3-alkylthiophene) and Absence in Poly(3-alkylfuran): A Theoretical Study of Conformation Defect in Polymer Chain

抄録

The conformation defect in polythiophene and polyfuran has been studied based on their optimized geometries using the semi-empirical tight-binding SCF-CO (self-consistent crystal orbital) method. It has been demonstrated that the total energy, the ionization potential and the band gap energy increase with increasing torsion between rings for both polymers. From the viewpoint of the total energy, however, polyfuran is difficult to have the conformation defect in comparison with polythiophene. The π-conjugation length along the polymer chain is largely decreased due to the existence of the conformation defect in polythiophene substituted with alkyl side chain induced by the steric hindrance at high temperature but not in substituted polyfuran.