P116
STEADY STATE AND TIME RESOLVED SPECTROSCOPIC STUDIES IN
DIFFERENT ENVIRONMENTS IN INDOLE-2-CARBOXYLIC ACID
AND INDOLE-5-CARBOXYLIC ACID:
A CASE OF EXCITED STATE PROTON TRANSFER
Prakriti Ranjan Bangal and
Sankar Chakravorti
Department of Spectroscopy
Indian Association for the Cultivation of Science
Intramolecular excited state proton transfer in Indole-2-carboxylic acid (I2C) and Indole-5
carboxylic acid (I5C) were investigated in various solvents in acidic, basic and in neutral media
by steady state and time resolved fluorescence spectroscopy. Hidden dual fluorescence of I2C
in polar and nonpolar solvents and distinct dual fluorescence of I5C in nonpolar solvents and
broad structureless fluorescence band in polar solvent are assigned to be arising out from
Franck-Condon excited state and from proton transferred excited state i.e. from zwitterionic
form, respectively. The excited state proton transfer equilibrium constant was calculated from a
fluorescence band shape analysis and its large solvent dependence arises primarily from local
solute-solvent interaction. Only mono-exponential fluorescence decay giving the lifetime
irrespective of the emission wave number was resolved (time resolution 500ps) and this provide
proton transfer to be considerably faster than fluorescence decay. Quantum chemical
calculations with AM1 Hamiltonian have been performed to confirm experimental findings
qualitatively.
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