Nonlinear optics of molecular donor–acceptor compounds

Molecular donor–acceptor–donor trimer is considered as a model system to study the effects of electron-intramolecular vibration coupling on the nonlinear optical properties. The static polarisability α and the static second hyperpolarisability γ are calculated and their dependencies on the model parameters are analysed. The compounds with molecules of low symmetry are predicted to have a potential for a high nonlinearity. Sharp changes of hyperpolarisabilities are expected upon neutral-to-ionic transition in the bis-tetrathiafulvalene-iodanil compound.