Solvent and vibrational effects on linear and non-linear spectral properties of push-pull chromophores

The two-state model for push–pull chromophores is extended to self-consistently account for the coupling of electrons to molecular vibrations and for the interaction with the solvent. The exact solution of this model proves that sum over states (SOS) expansions of NLO responses and standard approaches to spectral properties fail for highly non-linear systems like push–pull chromophores. Alternative approaches are discussed.