D. Banerjee, A. Mandal, S. Mukherjee
2003
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Journal
Journal of the Indian Chemical Society
Abstract
The absorption and emission properties of 4-hydroxy-3-formylbenzoic acid (HFBA) have been studied in some nonpolar and weakly polar solvents in relation to 4-methyl-2,6-diformylphenol (MFOH) at room temperature and 77 K. The excited state intramolecular proton transfer (ESIPT) is evidenced by a large Stokes shifted emission (∼11448 cm - 1 ) which is likely to originate from the enol tautomer. The stable molecular structure in the ground state of HFBA is found to be an intramolecularly hydrogen bonded closed conformer from which proton transfer takes place in the first excited singlet (S 1 ) state. Proton transfer in the ground and excited state of HFBA has also been studied in dioxane/cyclohexane and tetrahydrofuran/cyclohexane solvent mixtures using steady state spectroscopy. At 77 K, HFBA exhibits phosphorescence in dioxane and only in presence of a base in n-hexane and 3-methylpenpruetane (3MP). It has been proposed that like MFOH, phosphorescence occurs due to the rotation of the formyl group present in HFBA.