A series of isopolymolybdate-viologen compounds: structures and photochromic, organic amine sensing, and double anti-counterfeiting properties

In this article, by introducing two isomers of [MoO] anions and a symmetrical viologen ligand, we synthesized three compounds 1–3 with different structures under solvothermal conditions, namely {Zn(1,3–bcbpy)(HO)[H(β-MoO)]}·2HO·2CHN (1), [Co(1,3-bcbpy)(HO)(γ-MoO)]·16HO (2) and {Ni(1,3-bcbpy)(HO)[H(γ-MoO)]}·4HO·2CHN (3) (1,3-bcbpy·2Cl=1,1′-bis(3-carboxybenzyl)-4,4′-bipyridine dichloride). The metal organic unit [Zn(1,3-bcbpy)] of compound 1 has a “bowknot-like” structure, while the free β-Mo anions are connected to the bow by hydrogen bonding. Compound 2 is a typical ABAB stacked 2D layer supramolecular structure, while compound 3 is composed of parallel 1D chains, which are connected to form a 2D layer structure through the coordination of Ni atom and the O atom of γ-Mo. Due to the reversible photochromic properties and excellent fluorescence quenching effect of compounds 1–3, we have successfully prepared flexible UV detectors based on 1–3. When 2 and 3 were exposed to amine atmosphere, they exhibited significant color changes for NH and ethanediamine. Based on this characteristic, we prepared amine colorimetric test paper. In addition, 1 can also be used as a new printing material medium, which can be practically applied to erasable inkless printing, and can also be used as a material with dual anti-counterfeiting properties.