Solvatochromic fluorescent styryl pyrene probes for the quantitative determination of water content in organic solvents

A series of D-pi-A fluorescent styryl pyrene probes were synthesized through the Wittig reaction. The introduction of an electron-withdrawing substituent on the phenyl ring creates a push-pull system that shows solvent -dependent intramolecular charge transfer (ICT) and solvatochromic properties. Among these, the styryl pyr-ene probes with nitro (Py-NO2) and aldehyde (Py-CHO) substituents exhibited remarkable sensitivity to envi-ronment polarity. They show remarkable fluorescence changes from green to red, and blue to orange in nonpolar to polar organic solvents, respectively. The results were explained by the Lippert-Mataga and ET(30) models, which were supported by theoretical calculations by the density functional theory (DFT). Importantly, the fluorescence emission of Py-NO2 in organic solvents is sensitive to the presence of water in the range of 0-34.2% (v/v) in THF, 0-9.1% (v/v) in DMF, and 0-39.7% (v/v) in CH3CN. The limits of detection of water were established as low as 0.007%, 0.033%, and 0.036% (v/v) in THF, DMF, and CH3CN, respectively. Py-CHO showed somewhat higher limits of detection than Py-NO2 for the same solvents but exhibited a broad linear response to water content in EtOH between 3.3 and 63.6% (v/v) water content with the limit of detection at 2.350% (v/v). Thus, it is possibly useful as a sensor for the wide range detection of alcohol content in beverages. These push-pull styryl pyrene probes not only served as a new supersensitive fluorescent sensor for the quan-titative detection of low to medium-level water content in organic solvents but may also be useful in a broad range of applications.