Multi‐Stimuli Responsive Luminescence and Domino Phase Transition of Hybrid Copper Halides with Nonlinear Optical Switching Behavior

Abstract Although phase transition materials (PTMs) under external stimuli are of great research interest duo to their rich potential applications, it is still challenging to explore multi‐responsive PTMs. Herein, two different phases of organic–inorganic hybrid copper‐based halides, α‐ and β‐Gua 3 Cu 2 I 5 (Gua + =CN 3 H 6 + ), were synthesized by solvent evaporation method, which they crystalize in the noncentrosymmetric space group Fdd 2 with zero‐dimensional structure and centrosymmetric space group C 2/ c with one‐dimensional metal‐halogen framework, respectively. Interestingly, it is firstly demonstrated that Gua 3 Cu 2 I 5 simultaneously possesses reversible PL conversion and NLO switching properties in response to thermal stimulus. Strikingly, apart from heat, its structural phase transition can also be triggered by crystalline‐phase‐recognition (CPR) and mechanical force. These new findings may pave a path for future exploration of PTMs with multiple physical properties.