Hydrazone fluorophores with acidochromism, mechanochromism, and solvatochromism for moisture detection

Water monitoring in organic solvents is crucial but remains challenging. Karl Fischer titration can reach ∼1 ppm but relies on toxic reagents and bench-top equipment; most fluorescent probes, in contrast, cover <10 % (v/v) water and provide only a single read-out. Here we introduce two triphenylamine functionalized hydrazone probes, DHB and DHF, that overcome these limitations by simultaneously translating water stimuli into three independent, quantitative fluorescence signals-wavelength, intensity and RGB color-within a single measurement. Their photophysical properties, including large Stokes shifts and ICT characteristics, were thoroughly investigated using UV-vis absorption, fluorescence spectroscopy and DFT calculations. A strong TPA donor and hydrazone acceptor generate an ICT push-pull system whose emission is selectively quenched when water hydrogen-bonds to the carbonyl and imine sites, yielding ratiometric wavelength and intensity shifts. In THF, ACN, DMSO and EtOH the fluorescence response is linear from 10 to 80 % water (R² > 0.99); DHF achieves an LOD of 0.0016 % (v/v) in DMSO with a rapid response. The maximum RSD is 3.4 %, confirming acceptable repeatability. DHB is highly selective for water; common interferents such as glucose, and aldehydes elicit negligible fluorescence changes. Triple-mode readouts enable accurate quantification of water in liquor samples, while the intrinsic acidochromism upon exposure to TFA/TEA vapors, mechanochromism and solvatochromism of the hydrazone scaffold offer additional channels for anti-counterfeiting, stress sensing and pH detection, extending the utility of these probes far beyond water analysis and further expanding the family of hydrazone luminogens.