Signaling of water content in organic solvents by solvatochromism of a hydroxynaphthalimide-based merocyanine dye

• A new merocyanine dye based on 4-hydroxynaphthalimide 1 was prepared.
• Sensor 1 shows pronounced negative solvatochromism in response to solvent polarity.
• Ratiometry provides usable calibration plots for water content in organic solvents.
• Changes in λmax of absorption also provide tools for water content determination.

Determining the water content in organic solvents has attracted much research interest in view of its importance in various chemical processes. We investigated the signaling behavior of a benzothiazolium appended 4-hydroxynaphthalimide derivative 1 for the water content in water-miscible organic solvents such as tetrahydrofuran, acetone, dimethyl sulfoxide, acetonitrile, ethanol, and methanol using UV–vis and fluorescence spectroscopy. Probe 1 showed pronounced negative solvatochromism in common organic solvents and revealed excellent correlation between the 1/λmax value and Reichardt's ET(30) parameter. The response to the changes in water content in the surveyed organic solvents could be analyzed using a ratiometric approach. The dependence of the absorption maximum (λmax) on the changes in water content was also useful as a calibration plot. The fluorescence signaling behavior was less pronounced than that of the UV–vis signaling, but was still usable.

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