  Photophysical and photochemical dynamics of ground state and excited state
proton transfer reaction is reported for Pyrrole 2-Carboxyldehyde (PCL). Steady
state absorption and emission measurements are conducted in PCL. The
theoretical investigation is done by using different quantum mechanical methods
(e.g. Hartree Fock, DFT, MP2, CCSD etc.). The reaction pathway and two
dimensional potential energy surfaces are computed in various level of theory.
A transition state is also reported in gas phase and reaction filed
calculation. It is established that PCL forms different emitting species in
different media. A large Stokes shifted emission band, which is attributed to
species undergoing excited state intramolecular proton transfer, is observed in
hydrocarbon solvent. Intermolecular proton transfer is observed in hydroxylic
polar solvent. Experimental observations yield all possible signatures of
intramolecular and intermolecular proton transfer in excited state of PCL. The
origins of these signatures have been explained successfully using
corresponding quantum mechanical theories.
