Fluorescence studies on solvent-induced intramolecular charge separation in symmetric biaryls

Fluorescence studies on 5,5′-bi-benz[a]-pyrenyl reveal that the emitting state in polar solvents possesses a high dipole moment. Even in non-polar solvents such as n-hexane, dual fluorescence is emitted, with a structured twisted intramolecular charge transfer band. This puts an upper limit to the dipolar solvent fluctuations necessary to induce symmetry reduction and charge separation in the excited state. Theoretical guidelines to predict further cases of biaryls that exhibit charge separation in the excited state are derived.