Prediction of Second-Order Optical Nonlinearity of Trisorganotin-Substituted β-Keggin Polyoxotungstate

Abstract

The dipole polarizabilities, second-order polarizabilities, and origin of second-order nonlinear optical (NLO) properties of trisorganotin-substituted beta-Keggin polyoxotungstate [XW9O37(SnR)3](11-n)- (X = P, Si, Ge, R = Ph; X = Si, R = PhNO2, PhCCPh) have been investigated by using time-dependent density functional response theory. This class of organic-inorganic hybrid complexes possesses a remarkably large molecular second-order NLO response, especially for [SiW9O37(SnPhCCPh)3]7- (system 5) with the static second-order polarizability (beta(vec)) computed to be 1569.66 x 10(-30) esu. Thus, these complexes have the possibility to be excellent second-order nonlinear optical materials. Analysis of the major contributions to the beta(vec) value suggests that the charge transfer from the heteropolyanion to the organic segment along the z-axis plays the key role in the NLO response of [XW9O37(SnR)3](11-n)-. The computed beta(vec) values increase as a heavy central heteroatom changes in the order Ge > Si > P. Furthermore, nitro substitution on the aryl segment and the lengthening of organostannic pi-conjugation are more important in enhancing the optical nonlinearity, especially for the latter factor. The present investigation provides important insight into the origin of the NLO properties of trisorganotin-substituted heteropolyoxotungstate.