THE USE OF ELECTRON CRYSTALLOGRAPHY TO DETERMINE THE STRUCTURAL DEPENDENCE OF NONLINEAR OPTICAL PROPERTIES IN ORGANIC MOLECULES. Z. X Zhang, C. Gilmore* U. Kolb I. G. Voigt-Martin, Institut fur Physikalische Chemie der Universitat Mainz, Jakob welder weg 11, D-55099 Mainz, Germany, *Department of Chemistry University of Glasgow, Glasgow G12 8QQ Scotland, UK

4-Dimethylamino-3-Cyanobiphenyl was characterized with respect to linear and non-linear optical properties in the crystal as well as solution. The crystal structure was completely solved by a combination of electron diffraction and computer modelling as well as an ab initio determination using maximum entropy combined with log likelihood statistics. From this model u and static second order polarisability [[beta]] were calculated. Their relevance to the values obtained by a combination of polarisation dependent measurements of Electric Field Induced Second Harmonic Generation (EFISH) and Hyper Rayleigh Scattering (HRS) in solution are discussed.

The molecular second order hyperpolarisability tensor was found to be dominated by one single component. The orientations of the dipole and the vectorial parts of the second order polarisability allow a deeper insight into the non-linear optical properties of the crystal.