Relation between bond-length alternation and two-photon absorption of a push-pull conjugated molecules: a quantum-chemical study

The results of the semiempirical study of the structure/property relationships for the two-photon absorption cross-section (delta) of a series of prototypical pi-conjugated push-pull molecules are presented. The calculations of delta for the first charge-transfer (CT) excited state were performed as a function of the bond length alternation (BLA). The molecular hyperpolarizabilities (beta and gamma) were calculated using the finite-field (FF) method. The obtained data were analyzed based on the simple two-state models. A strong dependence of delta on the BLA parameter was noticed. (C) 2002 Elsevier Science B.V. All rights reserved.