2-PHOTON ABSORPTION AND 3RD-HARMONIC GENERATION OF DI-ALKYL-AMINO-NITRO-STILBENE (DANS) - A JOINT EXPERIMENTAL AND THEORETICAL-STUDY

The one- and two-photon optical absorption spectra as well as the freq uency dependent third-harmonic generation response of a side-chain pol ymer containing 4-dialkylamino-4'-nitro-stilbene (DANS) as its side gr oup have been measured over a wide range of frequency. A three-state m odel, based on an intermediate neglect of differential overlap/multire ference double-configuration interaction description of the excited st ates, provides a coherent picture of the dynamic response of DANS, but fails in reproducing the red shift observed when going from the linea r to the nonlinear absorption spectra; including vibronic coupling wit hin the Franck-Condon approximation improves the fit. (C) 1995 America n Institute of Physics.