The weak electronic coupling in ionic hybrid metal halides (HMHs) is conducive to integrating the photoactivity of organic components and mechanical properties of inorganic components. Therefore, HMHs can function as a suitable platform to advance the photomechanical performance because of their great structural designability and wide composition diversity. Herein, notable photosalient effect is observed in 0D ionic (LH)2InCl5 (1, L = 4-styrylpyridine). Upon irradiating 450 nm light, 1 undergoes a rare single crystal-to-single crystal transformation to (L2H2)In(H2O)Cl5 (1a) along with distinct photochromic photoluminescence and various photomechanical responses, driven by the cascade photoinduced [2+2] cycloaddition of LH+ and water sorption by coordinatively unsaturated In3+. Detailed mechanistic investigation unravels the photosalient effect is initiated by the cycloaddition reaction and enhanced by the water sorption, which makes the phase transformation more energetically and kinetically favorable through decreasing Gibbs free energy (1.51 eV) and kinetical energy barrier (0.29 eV). Additionally, the partially reversible transformation between LH+ monomers and dimers endows 1a excellent photoswitch performance due to the variation of π electron conjugated degree for LH+. At last, by integrating powdered 1 with polymethyl methacrylate (PMMA), 1-PMMA hybrid matrix membrane exhibits fast and controllable responsive behaviors including bending and curling through controlling the direction of concentration gradient. This work demonstrates that ionic HMHs might funtion as a promising platform for advanced photomechanical and photochromic materials.
