Fluorescence of an excitonic gas of long segments

The photophysics of polysilanes and poly(p-phenylenevinylene) indicates rapid energy transfer to, and fluorescence from, long segments that form a fixed dilute array in films. We model exciton formation due to π-electron dispersion forces between long segments and show that delocalization leads to bimodal emission, as observed in PPV. Dispersion preferentially stabilizes cluster states with small transition moments to the ground state.