Experimental demonstration of the relationship between the second- and third-order polarizabilities of conjugated donor-acceptor molecules

摘要

Abstract: The dependence of the second- and third-order polarizabilities ($beta and $gamma@) on ground-state polarization was measured for a series of donor-acceptor polyenes using electric field induced second harmonic generation and third harmonic generation, respectively. The changes in ground-state polarization, associated with the donor/acceptor strength or solvent polarity, were probed by x-ray crystallography, $+1$/H-NMR, electronic absorption, and Raman spectroscopies. The observed behavior of $beta and $gamma as a function of ground- state polarization agrees well with theoretical predictions. In particular, positive and negative peaks, as well as sign changes, were observed for both $beta and $gamma@. The dependences for $beta and $gamma are consistent with a derivative relationship between them. In addition, the third-order polarizability of a series of molecules possessing zero bond length alternation was found to be negative, in agreement with predictions based on the relationship between the polarizabilities and ground-state geometry. !19