Microwave-assisted ionothermal synthesis of a water-stable Eu-coordination polymer: a Ba2+ ion detector and fluorescence thermometer

A water-stable Eu-coordination polymer (CP), namely [HMIm]Eu(DHBDC)(2) (1) (HMIm = 1-hexyl-3-methylimidazolium; H2DHBDC = 2,5-dihydroxytelephthalic acid), was obtained using ionothermal synthesis. 1 represents the first coordination polymer capable of qualitative and quantitative detection of Ba2+ in aqueous solutions with a fluorescent enhancement that is visible to the human eye, which can be ascribed to the formation of fluorescent compound Ba(DHBDC) (2) during the detection process. Temperature-dependent photoluminescence (PL) makes 1 a potential material for a fluorescence thermometer. Furthermore, the detection process for Ba2+ using 1 turns the one-PL transition fluorescence thermometer into a two-PL transition fluorescence thermometer, increasing the accuracy of the fluorescence thermometer.