Detection and discrimination of water (H2O) and heavy water (D2O) by an off-the-shelf fluorescent probe

Coumarin based small molecule 6,7-dihydroxycoumarin or Esculetin (ES) has been used for the colorimetric and fluorogenic detection of trace amount of water in acetonitrile, acetone and 1,4 dioxane. The deprotonated (anionic) form of ES namely ES-F is reprotonated by trace amount of water. It was observed that the compound ES itself act as a water sensor through formation of hydrogen bonding interaction with the water. But, the probe ES-F shows high sensitivity in acetonitrile as low as the limit of detection (0.0167 wt%). ES-F found to be more sensitive for moisture detection as compared ES. Di-hydroxide group present in the ES play an essential role in sensing the moisture in the organic solvent and it was confirmed by a model compound. Further, taking advantage of basic nature of D2O, compound ES was used as an efficient optical sensor to detect D2O in organic solvents and H2O contamination in D2O. The response mechanism of sensor ES to D2O is based on deprotonation. The different spectral behaviour of ES with D2O and water also used to discriminate between D2O and H2O. The probe ES has many advantages such as economical, readily available, no multistep chemical synthesis, good sensitivity, fast response and used to discriminate D2O and H2O.