A solvatochromic cyanostilbene derivative as an intensity and wavelength-based fluorescent sensor for water in organic solvents

A novel solvatochromic fluorescent cyanostilbene derivative 1 with a D-p-A structure was synthesized. The introduction of an electron-donating methoxy group and an electron-accepting nitro group into the p-conjugated cyanostilbene bridge offered an intense intramolecular charge transfer (ICT) process in molecules and endowed 1 with a prominent solvatochromic emission property. Compared with the moderate changes in its absorption spectra in the different solvents, the emission of 1 was strongly dependent on the solvent polarity and could be tuned from blue to red by changing the solvent from apolar toluene to polar dichloromethane (DCM). Significantly, 1 can function as an efficient intensity and wavelength-based fluorescent sensor for the detection of trace water in THF and dioxane, respectively. A low detection limit of 71 ppm in THF made it a supersensitive water sensor for practical applications. A remarkable red shift of about 45 nm in dioxane made 1 an efficient wavelength-based fluorescent sensor for water avoiding external disturbance, whose emission color can be easily observed and distinguished by the naked eye. Moreover, the easy-to-prepare test papers loaded with 1 provide a simple and low cost protocol for the qualitative and quantitative detection of the water content in organic solvents without resorting to instrumental analysis.