Excited state photodynamics of 4-N,N-dimethylamino cinnamaldehyde:: A solvent dependent competition of TICT and intermolecular hydrogen bonding

This paper describes the dual fluorescence of 4-N,N-dimethylamino cinnamaldehyde (DMACA) in various solvents. Based on major findings the first fluorescence band has been assigned to be arising out of delocalized excited state (DE) and the anomalous fluorescence band in polar aprotic solvents has been assigned to twisted intramolecular charge transfer (TICT) state whereas, in protic solvent it is arising out due to hydrogen bonding interaction between hydrogen donor part of the solvent and carbonyl group of the probe molecule. This hydrogen bonding being an efficient fluorescence quenching channel trammels the TICT formation and thus an apparent competition exists between TICT and hydrogen bonding formation in protic solvent. The calculated absorption spectrum generated from CNDO calculations follows nicely the experimental absorption band. The AM1 calculations corroborate the large dipole moment change and the charge transfer in orthogonal position as found from experimental observations. (C) 2001 Elsevier Science B.V. All rights reserved.