Organic Second-Order Nonlinear Optical Materials with Transparency in the Blue Wavelength Region: Ethylene Derivatives Possessing Electron-Donor and Acceptor Groups

Abstract

Abstract A series of ethylene and methanimine derivatives possessing both electron-donor and -acceptor groups were synthesized in order to obtain frequency doublers of infrared semiconductor lasers. Their second-harmonic-generation (SHG) was investigated by means of a powder method and an electric-field-induced second-harmonic method. Three ethylene derivatives were found to be SHG active without any absorption in the blue wavelength region. X-Ray crystallographic analyses were made for two of them. It was found that strong donor and acceptor substituents tend to twist the central C=C double bond, thereby resulting in smaller β-values than those expected for non-twisted molecular structures. Based on the molecular and crystal structures, some strategies are presented regarding the synthesis of SHG materials of these push-pull ethylenes and methanimines.