An Optimal Arrangement of (H<sub>2</sub>C<sub>4</sub>N<sub>2</sub>O<sub>3</sub>)<sup>2–</sup> Groups in the First Non-Centrosymmetric Alkali Barbiturate Li<sub>2</sub>(H<sub>2</sub>C<sub>4</sub>N<sub>2</sub>O<sub>3</sub>)·2H<sub>2</sub>O Inducing a Giant Second Harmonic Generation Response and a Striking Birefringence
Donghong Lin, Min Luo, Chensheng Lin, Liling Cao, Ning Ye
Abstract
Ionic inorganic–organic ultraviolet (UV) nonlinear optical (NLO) materials have gradually become attractive because they can integrate their advantages into one. In this study, the first non-centrosymmetric alkali dihydro-barbiturate, Li2(H2C4N2O3)·2H2O, was successfully synthesized by a mild hydrothermal method. Li2(H2C4N2O3)·2H2O has a short ultraviolet cutoff edge (∼261 nm) due to the introduction of the inorganic Li ion. Besides, owing to being nearly coplanar and the π-conjugated organic (H2C4N2O3)2– groups being parallel to each other, Li2(H2C4N2O3)·2H2O exhibits a very strong second harmonic generation response (10.8 × KH2PO4) and a quite large birefringence (0.218@546 nm). These superior linear and nonlinear properties make Li2(H2C4N2O3)·2H2O a promising UV NLO material.