New Thiolated Nitrophenylhydrazone Crystals for Nonlinear Optics

Abstract

We investigate new 4-nitophenylhydrazone crystals with thiolated electron donors for nonlinear optical applications. The methylthiolated (SM) electron donor and the biphenyl sulfane (SB) electron donor, which promotes a herringbone packing motif, are incorporated with an acentric nonlinear optical core, nitrophenylhydrazone (NPH), which promotes a lambda-shaped packing motif in the crystalline state. SM-NPH (4-(methylthio)benzaldehyde-4-nitrophenylhydrazone) crystals show head-to-tail hydrogen-bonded chains, which outweigh the usual lambda-shaped packing of the nitrophenylhydrazone group. SB-NPH crystals (4-(phenylthio)benzaldehyde-4-nitrophenylhydrazone) show simultaneous lambda-shaped packing, based on the hydrogen bonds of nitrophenylhydrazone with the nitro electron acceptor group, and the herringbone-shaped packing of biphenyl sulfane groups. Polar SM-NPH chains pack in a centrosymmetric crystal structure, while SB-NPH crystals exhibit a large macroscopic second-order nonlinearity resulting from an acentric molecular ordering of two rotational isomers. In addition, SB-NPH crystals undergo an irreversible phase transition before melting, with the second phase being also acentric with a strong second harmonic generation efficiency.