Water-Induced Turn-on of Lanthanide Photoluminescence Emission and Application in Colorimetric Sensing of Trace Water

To examine the water-induced photoluminescence turn-on and its potential application in trace water sensing, a new series of [LnIII(dmba)3(H2O)2]·2H2O, where LnIII = LaIII (I), PrIII (II), NdIII (III), SmIII (IV), EuIII (V), GdIII (VI), TbIII (VII), DyIII (VIII), HoIII (IX), and ErIII (X), were synthesized using dimethoxybenzoic acid (Hdmba). Their single-crystal structures and thermal and chemical robustness were investigated, and the effects of lanthanide contraction and noncovalent interactions were discussed. The photoluminescence and colorimetric properties of I–X were investigated. Their dependence on dehydration and rehydration was disclosed, from which the significant role of noncovalent interactions was proposed. Based on the dehydration–rehydration-dependent responses in the forms of photoluminescence emission and color, the turn-off (dehydration) and turn-on (rehydration) of the red emission of EuIII (V) were demonstrated. Using a mobile phone camera and freeware application, its use in the colorimetric sensing of trace water in polar organic solvents was successfully achieved. With respect to ethanol, acetonitrile, and acetone, linear correlations were established from 0 to 3–5% by volume of water with an R2 of over 0.98. The detection and quantification limits were less than 0.5 and 1.5%, respectively. The percentage recoveries were 92 and 110%. The underlying mechanism was postulated.