Polaron–excitons and electron–vibrational band shapes in conjugated polymers

The neutral excitations in poly(p-phenylenevinylene) are studied in conjunction with the vibronic structure of the lowest optical transitions. Combining the configuration interaction of Wannier-localized electron–hole pairs with an empirical description of electron–phonon coupling, we obtain the potential energy surfaces of monoexcited states and the Condon electron–vibrational spectra in absorption and emission. The S1→S0 luminescence band shape is found compatible with self-localization of S1 within about 10 monomers, driven exclusively by electron–phonon coupling. The singlet and triplet polaron–excitons are exchange–split by about 1 eV and differ substantially in terms of average electron–hole separation.