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SOLVENT EFFECTS ON THE ELECTRONIC ABSORPTION AND FLUORESCENCE SPECTRA OF INDOLE‐4‐CARBOXYLIC ACID: PROTOTROPIC EQUILIBRIA IN AQUEOUS SOLUTIONS
Author(s) -
Krishnamurthy Mannam,
Mishra Ashok K.,
Dogra Sneh K.
Publication year - 1987
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1987.tb05387.x
Subject(s) - chemistry , deprotonation , protonation , indole test , photochemistry , excited state , molecule , carboxylic acid , dipole , fluorescence , ground state , singlet state , absorption (acoustics) , absorption spectroscopy , aqueous solution , solvent , stereochemistry , organic chemistry , materials science , ion , physics , quantum mechanics , nuclear physics , composite material
— The absorption and fluorescence spectra of indole‐4‐carboxylic acid in various solvents have indicated that the ‐COOH group is more planar with respect to the indole ring in the first excited singlet state (S 1 ) than in the ground (S 0 ) state. Relatively large Stokes' shifts indicate that polarisability and dipole moment of the molecule are increased predominantly upon excitation. Prototropic reactions in the S 0 and S 1 states are the same. The ‐COO ‐ and ‐COOH+ 2 groups are not coplanar in the S 0 , but coplanar in the S 1 state. pH‐dependent fluorescence spectra have revealed that both protonation and deprotonation of the ‐COOH group increase the basicity of the molecule upon excitation.