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.

Automated summary

This study reinvestigated the photochemistry of 2,5-dihydroxy benzoic acid in various organic solvents and aqueous solutions with different pH values. Different forms of DHBA were identified in different solvents and the observed significant Stokes shift in emission was attributed to excited-state intramolecular proton transfer.