STRUCTURAL DEPENDENCE OF NONLINEAR-OPTICAL PROPERTIES OF 4-DIMETHYLAMINO-3-CYANOBIPHENYL

4-Dimethylamino-3-cyanobiphenyl (4-DMA-3-CB) was characterized with re spect to linear and nonlinear optical properties in a crystal as well as in solution. The crystal structure was studied dependent on the cry stallization conditions. It is shown that the crystal structure exhibi ting NLO-activity can completely be solved by a combination of electro n diffraction and computer modeling. There are four molecules per unit cell in the space group Pna2(1) with dimensions a = 10.28 Angstrom, b = 22.64 Angstrom, c = 5.27 Angstrom. From this model structure the va lues and orientation of the dipole mu and static second order polariza bility beta can be calculated. Their relevance to the values obtained by a combination of polarization dependent measurements of Electric Fi eld Induced Second Harmonic Generation (EFISH) and Hyper-Rayleigh-Scat tering (HRS) in solution are discussed. The molecular second order pol arizability tensor was found to be dominated by one single component. The orientations of the dipole and the vectorial parts of the second o rder polarizability delivered by the semiempirical calculations are in good agreement with the results of the EFISH and HRS-measurements and allow a deeper insight into the nonlinear optical properties of the c rystal.