New phenolic N-methylquinolinium single crystals for second-order nonlinear optics

Abstract Highly efficient nonlinear optical quinolinium single crystals are newly designed and synthesized. The quinolinium single crystals consist of a 2-(4-hydroxystyryl)-1-methylquinolinium cation possessing large molecular optical nonlinearity and a 2,4,6-trimethylbenzenesulfonate counter anion. The quinolinium crystals exhibit monoclinic acentric space group P2 1 symmetry, resulting in large macroscopic nonlinear optical response, which is comparable with those of highly nonlinear optical configurationally locked polyene crystals. Plate-shaped bulk quinolinium crystals with an area of up to 56 mm 2 are successfully grown by the solution growth method. Single quinolinium crystals exhibit a large transparency range (550–1600 nm) in the optical region and a relatively low absorption coefficient in the THz region.