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In this work, the single crystal to single crystal (SCSC) transformations in three mononuclear copper complexes [CuL22]Cl2·2H2O (1), [CuL12Cl2] (2), and [CuL22]Cl2·4H2O (3) (L1= di-2-pyridyl ketone, L2= di(pyridin-2-yl)methanediol) are realized by the irreversible dehydration and hydration reaction of L1and L2. Dark purple crystal 1is obtained by self-assembly of L1and CuCl2·2H2O in solvothermal reactions, in which the carbonyl group of L1undergoes a hydration addition reaction to form L2. On heating, 1transforms to 2by dehydrating water accompanied by the change of the color and coordination octahedron of CuIIions. In a saturated water vapor environment, 2can absorb six water molecules and transform to 3with the same color and coordination environment with 1but different lattice water. The SCSC process from 2to 3is reversible: 3can transform back to 2on heating like that of 1. Chroma rewritable behaviors in the structural transformation of the complexes make them visually identifiable temperature or water probes.

Multifunctional materials have always been an attractive research area, but how to combine multiple excellent properties in one compound remains a considerable challenge. Organic–inorganic hybrid compounds are widely used in the design of such materials due to their rich properties and flexible assembly. Herein, two new manganese(II)-based organic–inorganic hybrid compounds, (C6NH16)2MnBr4(1) and (C7NH18)2MnBr4(2), are prepared by the solution method. Compounds 1and 2both emit extremely strong green light under UV excitation, with high quantum yields of 45.93 and 50.98%, respectively. In addition, reversible solid-state phase transitions and obvious switchable dielectric properties are shown at 378/366 and 361/352 K, respectively. The coexistence of the dual stimulus–response characteristics of temperature and light in compounds 1and 2opens a new path for exploring more multifunctional phase transition materials.