Photo-, Thermo-, Electrochromic, Erasable Inkless Printing, Ions Detection, and UV Detector Properties of Viologen Compounds Based on Homomolybdate/Keggin POMs

Three POMs-based viologen compounds with different structures were successfully constructed under solvothermal and hydrothermal conditions, [Cu(1,4-cby)(2)(H2O)(0.5)(beta-Mo8O26)(0.5)]<middle dot>C3H7NO<middle dot>3H(2)O (1), [H-2(1,4-cby)(2)]<middle dot>(beta-Mo8O26) (2) (1,4-cby<middle dot>Cl = 1-(4-carboxybenzyl)-4,4 '-bipyridine chloride), [H-2(1,4-cbyy)(2)]<middle dot>(SiMo12O40) (3) (1,4-cbyy<middle dot>Cl = 1-(4-cyanobenzyl)-4,4 '-bipyridine chloride). Compound 1 is a structure with the number "eight-like" metal-organic chain with Cu as the nodes, and compounds 2 and 3 are fascinating structures connected by hydrogen bonding interactions. More importantly, compounds 1-3 exhibit a good response to both light and electricity and the thermal response of compound 1 was also studied. The reasons for the response of compounds 1-3 to external stimuli were analyzed through methods such as UV-Vis, EPR, and XPS. In addition, the transient photocurrent response results of compounds 1-3 are the same as those obtained from kinetic calculations. Meanwhile, the coated filter paper based on compound 3 has been successfully applied in erasable inkless printing and anti-counterfeiting, the test paper of 3 can also detect metal ions, and the films based on compounds 1-3 are a flexible and portable ultraviolet (UV) detector.