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 (H 2 O) 0.5 (β-Mo 8 O 26 ) 0.5 ]·C 3 H 7 NO·3H 2 O ( 1 ), [H 2 (1,4-cby) 2 ]·(β-Mo 8 O 26 ) ( 2 ) (1,4-cby·Cl = 1-(4-carboxybenzyl)-4,4'-bipyridine chloride), [H 2 (1,4-cbyy) 2 ]·(SiMo 12 O 40 ) ( 3 ) (1,4-cbyy·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.