Chiral Lead-Oxyiodide Nonlinear Optical Crystals Constructed on l-Malate Groups.

The pursuit of nonlinear optical (NLO) crystals exhibiting an exceptional second-harmonic generation (SHG) response has been a persistent objective in scientific research. Herein, three chiral lead-oxyiodide NLO crystals, [Rb2I][PbI(LM)] (LM = L-OOCCH2CH(OH)COO) and A2[Pb2I2(LM)2] (A = Rb, K), have been rationally synthesized by introducing the l-malate group into halide perovskites to substitute partial halide anions. All of them contain highly distorted lead-oxyiodide polyhedra with large hyperpolarizability and anisotropic polarization. In particular, the highly distorted [PbI2O4] polyhedrons in [Rb2I][PbI(LM)] are shielded by more Rb+ cations and aligned into a uniform arrangement. As a result, their microscopic second-order susceptibilities are optimally superposed. Remarkably, [Rb2I][PbI(LM)] exhibits a very strong SHG response of 7.3 × KDP that is nearly three times those of A2[Pb2I2(LM)2] (A = Rb, K), as well as the largest among malates to date. Theoretical calculations demonstrate that their SHG responses mainly arise from highly distorted lead-oxyiodide polyhedrons. This study offers a viable strategy for the exploration of high-performance NLO crystals.