SPECTROSCOPIC EVIDENCE FOR ASYMMETRIC POLARON STATES IN POLY3-(4-OCTYLPHENYL)-THIOPHENE!

The strong electron-phonon coupling present in conjugated polymers has been amply demonstrated in the existence of solitons, polarons and bi polarons. For the non-degenerate ground state systems, the early theor y of Campbell, Fesser and Bishop only considered Hamiltonians With exp licit electron-hole symmetry. As a consequence, two of the allowed opt ical transitions of polarons are degenerate, and in total three absorp tion features are expected below the bandgap transition. We report spe ctroscopic observation of a polaron state in a polymer from the polyth iophene family, poly3-(4-octylphenyl)-thiophene!. This polymer shows four distinct optical transitions below the bandgap. This, we suggest, is due to the broken electron-hole symmetry due to coupling between t he conjugated main chain and the aromatic side chain.