Three polyoxometalate-viologen color-changing materials with excellent photo-, thermo- and amine-chromic properties

Three polyoxometalate-viologen (POMV)-based organic-inorganic hybrid compounds were constructed, namely [CuII(Cbipy)2(4,4′-bipy)](SiW12O40)·1.5C2H5OH·2.5H2O (1), (HCbipy)2·(β-Mo8O26) (2) and (HCbipy)2·(SiMo12O40) (3). Compound 1 shows a leaf like Cu-Cbipy chain with Keggin anions occupying the grid. Compounds 2 and 3 are discrete structures. These compounds exhibit color-changing properties by different external stimuli, such as photochromic and thermochromism as well as detecting organic amines and even UV-light. This article characterized the phase purity and stability of the compound using PXRD and FT-IR, and characterized the photochromic and thermochromic properties of the compound using UV-vis absorption spectrum, EPR, XPS and DFT calculations. And the compound was subjected to different amine atmospheres for amine discoloration research. Finally, the photochromic performance is applied to inkless erasable printing, where the desired pattern can be clearly printed through ultraviolet radiation. These observations provide valuable insights into design and synthesize electrostatic attraction drove POMV-based crystalline materials as color-changing materials.