Electronic Structures and Optical Properties of Organic DAST and DSTMS Crystal Materials

Abstract

The electronic structures and optical properties of 4-N,N-dimethylamino-4′-N′-methylstilbazolium tosylate(DAST) and 4- N,N- dimethylamino- 4′- N′- methylstilbazolium 2,4,6- trimethylbenzenesulfonate(DSTMS) were investigated using density functional theory based on the plane wave basis set. The results indicated that the two compounds showed similar band structures, and the top of the valence band and the bottom of the conductive band mainly originated from the N 2p states of dimethylamino and methylpyridine, respectively. In terms of the linear optical properties, the birefringence indexes, Δn, of the two compounds were very large(Δn0.5), and they exhibited good light transmission in the mid- and far-infrared regions. With regard to second-order nonlinear optical characteristics, the DAST and DSTMS crystals showed strong second harmonic generation(SHG) responses, and the corresponding SHG coefficients(d11) were about 150 pm V-1. Analysis of the band structures showed that the SHG responses of the two compounds were closely related to charge transfers between electron-donating and electron-withdrawing groups. Ethylene bridging also played an important role in the charge transfer process.