Study of Proton Transfer Reaction Dynamics in Pyrrole 2-Carboxyldehyde

TL;DR

This study investigates the proton transfer dynamics in Pyrrole 2-Carboxyldehyde using experimental spectroscopy and quantum mechanical calculations, revealing different proton transfer mechanisms in various solvents and identifying key reaction pathways.

Contribution

It combines experimental and theoretical approaches to elucidate excited state proton transfer mechanisms in PCL, providing detailed reaction pathways and potential energy surfaces.

Findings

PCL exhibits different emission species depending on the solvent.

Large Stokes shift observed due to excited state intramolecular proton transfer.

Intermolecular proton transfer occurs in polar hydroxylic solvents.

Abstract

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.