A COMPARATIVE-STUDY OF FIRST HYPERPOLARIZABILITIES OF THE ACIDIC AND BASIC FORMS OF WEAK ORGANIC-ACIDS IN WATER

Dynamic and static first hyperpolarizabilities (beta) of a series of b enzoic and cinnamic acids in water have been investigated. These acids exist in a mixture of acidic and basic forms in solution. The hyperpo larizability of the basic form is higher than that of the correspondin g acid form which is attributed to the red-shift of the absorption max imum of the basic form relative to that of the acid form. A ZINDO-corr ection vector (CV) method including solvent effects through a self-con sistent reaction held (SCRF) for computing beta reproduce measured val ues within experimental errors. Static oh initio hyperpolarizabilities within SCRF are slightly lower than the ZINDO/CV/SCRF beta's Semiempe rical as well as ab initio gas phase calculations show the correct exp erimental trend in beta but their magnitudes are much smaller than the measured values. (C) 1996 American Institute of Physics.