Theoretical design of organic chromophores with large two-photon absorption cross-sections

Design strategies and structure-property relationships for two-photon absorption in conjugated molecules are described on the basis of correlated quantum-chemical calculations. We first focus on stilbene derivatives with centrosymmetric structures. We found that derivatization of the conjugated molecule with electroactive groups in a quadrupolar-like arrangement leads to a large increase in the two-photon absorption cross section, δ. Next, we consider a noncentrosymmetric dipolar compound built by grafting donor and acceptor end-groups on stilbene. In this case also, the calculations predict huge enhancement factors in δ upon substitution. In both cases (centrosymmetric and noncentrosymmetric compounds), the quantum-chemical description provides rich insight into the mechanisms for the two-photon absorption phenomenon.