New phenolic organic salt crystals with large optical nonlinearity

New phenolic organic salt crystals exhibiting large macroscopic second-order optical nonlinearities have been developed. Two molecular anions, 4-bromobenzenesulfonate (BBS) and naphthalene-2-sulfonate (N2S), were incorporated with highly efficient nonlinear optical 2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium (OMQ) cationic chromophores into crystals. Both OMQ-BBS and OMQ-N2S crystals demonstrated second harmonic generation, which confirms their non-centrosymmetric molecular arrangement. Particularly, the OMQ-BBS crystals possess a non-centrosymmetric space group symmetry Cc with a high-order parameter due to a small molecular ordering angle of approximately 21°, resulting in a very large macroscopic second-order nonlinear optical susceptibility, with the effective first hyperpolarizability of about 105 × 10^–30 esu. Furthermore, the non-centrosymmetric crystal phase of the OMQ-BBS crystals exhibits remarkable thermal stability up to its melting temperature of 304 °C.

Graphical abstract

Newly designed phenolic organic styryl salt crystal, 2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium 4-bromobenzenesulfonate (OMQ-BBS), exhibits a large macroscopic second-order nonlinear optical susceptibility (105 × 10^-30 esu).