Revisiting the photochemistry 2,5‐dihydroxy benzoic acid (gentisic acid): Solvent and pH effect

In the present study, we have reinvestigated photochemistry of 2,5‐dihydroxy benzoic acid (DHBA) in a series of organic solvents of different polarities and the aqueous solution of varying pH from 1 to 14. The investigation was carried out using steady‐state and nanosecond (ns) time‐domain fluorescence measurement techniques at room temperature. Some hitherto not explored spectral features with new insight on different forms of DHBA are reported. It is found that DHBA exists as monoanionic and neutral forms in various polar protic, aprotic, and nonpolar solvents. In aqueous solution (pH 1 to 14), neutral, monoanionic, and dianion forms are found to be responsible for the observed optical spectral profiles. The observed significant Stokes shift in emission is attributed to species undergoing excited‐state intramolecular proton transfer (ESIPT) in different solvents. The analysis presented in this work elucidates and validate the presence of various species and conformers of DHBA. We have reinvestigated photochemistry of 2,5‐dihydroxy benzoic acid (DHBA) various organic solvents and aqueous solution of varying pH. Some hitherto unexplored spectral features with new insight on different forms of DHBA are reported. It is found that it exists as monoanionic, dianionic, and neutral forms depending upon solvent and pH. Significant Stokes shift is attributed to excited‐state intramolecular proton transfer (ESIPT). The analysis presented in this work validates various species and conformers.