Barbituric acid-based ICT probe as a reversible optical sensor for trace moisture detection

The presence of trace amounts of water as an impurity in organic solvents and materials can critically influence chemical reactivity and material performance, necessitating simple, sensitive, and reversible moisture detection methods. Herein, a barbituric acid-based intramolecular charge transfer (ICT) chromophore (1) is reported as a dual-mode colourimetric and fluorometric probe for trace moisture sensing. Probe 1 exhibits pronounced and reversible spectral changes upon exposure to water in common organic solvents, including THF, acetonitrile, ethanol, and DMSO, with the highest sensitivity observed in THF. Systematic spectroscopic investigations reveal that the sensing response arises from hydrogen-bondassisted aggregation mediated by the acidic protons of the barbituric acid moiety. The interaction is fully reversible, as demonstrated by fluoride-induced deprotonation followed by reprotonation in the presence of trace water. A structurally related analogue (2), lacking acidic protons, shows markedly diminished sensitivity, confirming the central role of hydrogen bonding in moisture recognition. The probe enables naked-eye, reusable moisture detection on TLC substrates and can distinguish between dry and moist soil and leaf samples through fluorescence quenching. These results establish compound 1 as a simple and reversible optical probe for trace moisture detection based on hydrogen-bond-driven aggregation.