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H. Arai, Y. Higashigaki, M. Goto, and S. Yano
[Jpn. J. Appl. Phys., Vol.33, No.10, pp.5755-5788, 1994]
An alpha-cyanostilbene crystal showing optical nonlinearity was examined to be compared with a non-optically active crystal, with emphasis on the structural aspect. It was suggested that the introduction of bulky substituents such dimethylamino and methoxy groups into the cyanostyrene conjugation system was effective to get macroscopic optical nonlinearity, based on the chemical synthesis and structural analysis. It was also stressed that the quadrupole interaction in alpha-cyanostilbenes was one of the important factors responsible for a nonsymmetric molecular arrangement for the second order optical nonlinearity.