Rational design of a solvatochromic coumarin aldehyde for the development of an effective water and humidity sensor

Reported herein is the design, synthesis, and water detection application of a highly solvatochromic coumarin derivative (compound 1), whose solvatochromism derives from the presence of both an electron-withdrawing aldehyde (i.e., formyl) substituent, and an electron-donating diethylamino group. Although this compound has been previously reported as a component of larger architectures, its solvatochromic properties as a stand-alone fluorophore have not been reported. Our investigations revealed that compound 1 demonstrated a high degree of fluorescence responsiveness to polar protic solvents, with a particularly strong decrease in its fluorescence occurring in the presence of small amounts of water. This water-based responsiveness was further exploited in the development of a fluorescent water sensor, which responds to both the presence of liquid water and water vapour with rapid, sensitive (detection limits as low as 0.05% (water/acetonitrile; v/v)), and irreversible fluorescence quenching.