Chain flexibility and nonlinear optical properties in polyenes within a two-state (VB-CT) model

We present a simple two-state model that justifies the dependence of first- order hyperpolarizabilities (ss) of push-pull polyenes on conformational di sorder. Particular relevance is given to the calculation of the vibrational properties (i.e. force constants, infrared and Raman intensities) which ar e used for the evaluation of the vibrational contribution to static molecul ar hyperpolarizabilities. The theoretical predictions are compared with exp erimental measurements of the quantities of interest on suitable molecules purposely synthesized. (C) 2001 Elsevier Science B.V. All rights reserved.