Three Anderson and octamolybdate based compounds modified by an asymmetric viologen: Photo-/thermo-chromic and luminescence properties

Abstract

In this work, POM anions and a viologen ligand were combined to construct appealing electron transfer chromotropic materials. Three kinds of POM-viologen hybrids were obtained in hydrothermal environment, namely [Cu2(1,4-Mbby)2(H2O)6(TeMo6O24)]·H2O (1), [Co2(1,4-Mbby)2(H2O)6(TeMo6O24)]·H2O (2), [Cu2(1,4-Mbby)4(H2O)2(β-Mo8O26)2] (3, 1,4-Mbby·Cl = (1-(4-Methyl-benzyl)-[4,4′]bipyridinyl-1-ium)chloridate). Among them, compounds 1 and 2 are isostructural, showing an infinite inorganic chain with Anderson anions linked by Cu/Co atoms. The 1,4-Mbby suspend on both sides of this chain. Compound 3 exhibits a Mo8 dimer with four 1,4-Mbby as “arms”. POM anions and viologen ligands form a classical donor-acceptor structure, which can promote electron transfer. Therefore, under thermal stimulation, compounds 1–3 show reversible thermochromic properties. Under light stimulation, 1 and 3 have good reversible photochromic properties. Moreover, compound 1 can detect aniline, and 3 can detect ammonia and ethylenediamine through discoloration. Interestingly, compounds 1–3 show luminescence characteristics. Especially, the bright blue fluorescence of 1 can be observed under the irradiation of a 365 nm ultraviolet lamp. Meanwhile, compounds 1–3 have good fluorescence quenching effect under illumination or heating conditions. In other words, these compounds can quickly sense light or heat with color change. This work broadens the applications of POM/viologen compounds in the fields of discoloration and luminescence.