Near-room-temperature reversible switching of quadratic optical nonlinearities in a one-dimensional perovskite-like hybrid

The switching of quadratic nonlinear optical (NLO) effects between two or more NLO states of solid-state materials represents an intriguing new branch in the field of photoelectrics and optics. While structural phase transitions have shown potential in this field, near-room-temperature reversible NLO switches have rarely been reported. To exploit new NLO switching materials within the structurally flexible class of hybrid perovskites, here, we synthesize a one-dimensional perovskite-like hybrid, (MP)PbBr3 (where MP+ is a 1-methylpyrrolidinium cation), through a facile solution method, which exhibits strong second harmonic generation (SHG) activities with an intensity of ~1.6 times as large as potassium dihydrogen phosphate. Intriguingly, (MP)PbBr3 enables the near-room temperature reversible switching of SHG properties, showing a large NLO switching contrast of up to ~40 between its SHG-active and SHG-inactive phases, beyond most of its liquid counterparts. Further microscopic structural analyses reveal that the dynamic ordering of the organic MP+ cation and inorganic chain-like skeleton triggers its centrosymmetric (P63/mmc) to acentric (P212121) phase transition at 316 K upon cooling, resulting in a crucial contribution to its NLO switching properties. This work illustrates the potential of this material as a candidate for solid-state NLO switches and will promote the development of NLO materials within the family of low-dimensional hybrid perovskites.