Synthesis and crystal structures of imidazolium salts for quadratic optical nonlinearities

• A series of new organic salts based on imidazolium are developed for second-order nonlinear applications.
• Nine single crystals have been obtained, among which two crystals show acentric crystal structure.
• DITMS crystal exhibits a large macroscopic optical nonlinearity and excellent crystal growth characteristic.
• The growth of the bulk DITMS crystal has been investigated.

We have developed a new organic cation core structure, trans-1-[p-(N, N-dimethylamino) styryl]-3-methylimidozalium for second order nonlinear optical (NLO) applications. Among the eight crystals of imidozalium salts with various counter anions, trans-1-[p-[(N, N-dimethylamino) styryl]-3-methylimidozalium 1-naphthalenesulfonate (II) (DINS-1(II)) and trans-1-[p-(N, N-dimethylamino) styryl]-3-methylimidozalium mesitylenesulfonate (DITMS) exhibit acentric crystal structures. The former belongs to Pna21 space group, while the latter crystallizes in Pn phase. The macroscopic optical nonlinearity of the acentric crystals have been estimated by Kurtz and Perry powder test at various grain sizes. Compared to DINS-1(II), DITMS exhibits a relatively large second order nonlinearity benefiting from the almost parallel arrangement of the main molecular charge–transfer axis in lattice. The growth of the bulk DITMS crystal has been investigated.

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