Syntheses, second-order NLO properties, and crystal structures of tetra-substituted ethylene, tri-substituted schiff-base, and diphenoxymethane derivatives

In order to obtain frequency doubler of the infrared semiconductor lasers, a series of push-pull ethylenes were synthesized. Among them, ethyl 2,2-bis(methylthio)-1-cyanoacrylate, ethyl 2-dimethylamino-2-methylthio-1-cyanoacrylate, and 2-dimethylamino-2-methylthio-1-cyanoacrylonitrile gave SHG with intensities of 5.5, 0.8, and 0.5 times, respectively, that of urea by a powder technique using an Nd: YAG laser as a fundamental wave. Their absorption edges located below 370 nm. The crystal structure analysis showed the distorted ethylene structure mainly due to the contribution of an intramolecular charge-transfer in their ground states. Their β values were calculated in an MNDO level. Diphenoxymethanes are expected to be Λ-shaped molecules and to favor columnar and non-centrosymmetric structures when packed in a crystal. Bis[p-(2,2-dicyanovinyl)phenoxy]methane, bis[p-(2-cyano-2-ethoxycarbonylvinyl)phenoxy]methane, and bis(p-bromophenylthio)methane gave SHG intensities 0.4, 1.4, and 0.1 times, respectively, that of urea.