Two helical conformations of polythiophene, polypyrrole, and their derivatives

Abstract

Two stable conformations, a planar or nearly planar rod and a coil, have been located on the potential-energy surfaces of several conducting polymers: polythiophene (PT), poly(3-methylthiophene) (PMeT), polypyrrole (PPy), and poly(3-methylpyrrole) (PMePy). The planar structure is slightly more stable for PT, PPy, and PMePy, while the coil configuration is preferred for PMeT. This finding could explain the existence of the coil conformation for poly(3-butylthiophene) in solution and for doped PMeT and PPy in the solid phase. We have identified a quinoid coil form of PT by our calculations, which strongly supports the presence of a coil conformation of doped PT derivatives. The band gap and total energy as functions of the conformation of PT indicate that the thermochromic behavior of PT derivatives results from the change in conformation with temperature. Similar behavior is expected for PPy derivatives. Vibrational analysis for helical and planar conformations of PT has been carried out, which identifies experimental possibilities in distinguishing among the rod versus coil conformations.