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 cinnamald ehyde (DMACA) in various solvents. Based on major findings the first fluore scence band has been assigned to be arising out of delocalized excited stat e (DE) and the anomalous fluorescence band in polar aprotic solvents has be en assigned to twisted intramolecular charge transfer (TICT) state whereas, in protic solvent it is arising out due to hydrogen bonding interaction be tween hydrogen donor part of the solvent and carbonyl group of the probe mo lecule. This hydrogen bonding being an efficient fluorescence quenching cha nnel trammels the TICT formation and thus an apparent competition exists be tween TICT and hydrogen bonding formation in protic solvent. The calculated absorption spectrum generated from CNDO calculations follows nicely the ex perimental absorption band. The AM1 calculations corroborate the large dipo le moment change and the charge transfer in orthogonal position as found fr om experimental observations. (C) 2001 Elsevier Science B.V. All rights res erved.