Nature of stokes shifted dual fluorescence in 2-acetyl-pyrrole: Tuning between intramolecular hydrogen bonding and ESIPT pathways

Abstract

Possibility of ground/excited state intramolecular proton transfer (GSIPT/ESIPT) have been studied in 2-acetyl-pyrrole (2AP) by theoretical (TDDFT, CASSCF) calculations and its experimental (spectral) verifications. Appearances of different conformers (C, T) and rotamers (Z, Z*) have been investigated by single absorption (284nm) and stokes shifted dual emission (375nm and 520nm) originating from ESIPT. Dual minima in PES scan show lowest energy state for C at S0 state. Small potential energy gap between two minima predicts the equal stability of C* and Z* in S1 state. Lower band gap (C*–Z*) validates barrier less ESIPT from C*→Z*.