Experimental investigation by UV–VIS and IR spectroscopy to reveal electronic and vibrational properties of pyrrole-2-carboxyldehyde: A theoretical approach

An effort to explain the ground state and excited state photophysics of pyrrole-2-carboxyldehyde (PCL) and its related compounds in ultraviolet–visible (UV–VIS) and infrared (IR) region has been reported in this paper. We have observed the mid-infrared absorption by using FTIR methods and obtained spectrum of PCL solid samples in the wavenumber region ranging from 450 to 4400 cm−1 with resolution 4 cm−1. Vibrational modes for observed dominant bands have been successfully explained with ab initio Density Functional Theory calculations. The experimental and theoretical data show the existence of intramolecular hydrogen bonding between H6…O11 of pyrrole and formyl group of PCL in ground state in nonpolar medium. From the values of different dipole moment, change in energy, heat formation, Gibbs free energy in both ground state and excited state optimized energy calculation, it shows that there is high possibility of intramolecular and intermolecular proton transfer from pyrrole group (NH) to formyl group (CO) in the excited state.