Three photochromic materials based on POMs and viologens for UV probing, visual detection of metal ions and amine detection

Abstract

In this work, by using two kinds of viologen ligands, three POM-based compounds were obtained under hydrothermal and solvothermal conditions, namely, {Cu₂(Cbybpy)₆(Cl)₂[H₄(β-Mo₈O₂₆)₃]}·12H₂O (1), (HCbybpy)₂·(β-Mo₈O₂₆) (2) (Cbybpy·Br = 1-(2′-cyano-biphenyl-4-ylmethyl)-[4,4′]bipyridinyl-1-ium bromide) and (HtBbbpy)₆·(β-Mo₈O₂₆)₂·(α-Mo₈O₂₆) (3) (tBbbpy·Cl = 1-(4-tert-butyl-benzyl)-[4,4′]bipyridinyl-1-ium chloride). The structures were characterized by FT-IR spectroscopy, PXRD and single crystal X-ray diffraction. These three compounds exhibit dissociative structures, in which there is a bi-nuclear Cu cluster in 1. Compounds 1–3 have a photochromic ability under irradiation of a Xe lamp with a filter (300–400 nm), showing fast photoresponse and different degrees of color change. Therefore, compounds 1–3 can be used in mixed matrix films for visible UV detectors. Compounds 1–3 also have photoluminescence properties with a good fluorescence quenching effect under irradiation. The powder samples of 1–3 can also be simply treated by ultrasonic treatment with ethanol solution and deposited on filter paper, which can be used as inkless and erasable printing materials. Taking compound 2 as an example, we prepared its metal ion detection test paper and realized the visual detection of Hg²⁺, Cu²⁺, and Co²⁺. Compounds 1 and 2 exhibit amine-selective sensing in contact with different amine vapors, so they can be used as organic amine detectors.