Four Polyoxometalate‐Viologen Discoloration Materials for UV Probing, Inkless and Erasable Printing and Visual Detection of Hg2+

Abstract In this work, four POM‐based compounds containing viologen ligands were synthesized, namely {CuII(tybipy)2(DMF)2[H2(β‐Mo8O26)]2} ⋅ 4 C2H7N (1), (Htybipy)2 ⋅ (β‐Mo8O26) (2) (tybipy⋅Br=1‐Thiophen‐3‐ylmethyl‐[4,4’]bipyridinyl‐1‐ium bromide), [CuII(nibipy)2(4,4’‐bipy)] ⋅ (SiW12O40) (3), (Hnibipy)2 ⋅ (δ‐Mo8O26) (4) (nibipy⋅Cl=1‐(4‐Nitro‐benzyl)‐[4,4’]bipyridinyl‐1‐ium chloride, 4,4’‐bipy=4,4’‐bipyridine). In compounds 1 and 3, Cu2+ and mixed organic ligands modify POM anions. On the other hand, 2 and 4 are supramolecular structures only containing ligands and anions. Under Xe lamp with filter (300‐400 nm) irradiation, these four compounds showed good photoresponse and photochromic ability, which can be used in mixed matrix films for visible UV detectors. Compounds 1–4 also have photoluminescence property and show good fluorescence quenching effect. A suspension of four compounds can be evenly spread on filter paper as inkless and erasable printing materials. Compounds 1 and 2 were also used as Hg2+ fluorescence detectors. The fluorescence intensity of 1 decreased by ca. 90 % when the concentration of Hg2+ increased to 40 mM. Moreover, we also prepared composites 1/2@Hg2+,1@Cu2+, 1@Co2+ by introducing 1/2 and Hg2+, Cu2+ and Co2+ to detection paper respectively, which can act as photochromic materials with features of fast color recovery.