The effect of hydrogen-bonding on the ultrafast electronic deactivation dynamics of indigo carmine

Abstract

Excited-state dynamics and mechanisms of the rapid deactivation process of indigo carmine (InC) were investigated by means of femtosecond transient absorption spectroscopy and steady-state Raman spectroscopy. Solvent dependence of the excited-state lifetime revealed that intermolecular hydrogen-bonding with the solvent molecule is more effective than the intramolecular ones to accelerate the deactivation process. Steady-state Raman spectra in the low-frequency region indicated a loss of molecular planarity in protic solvents. It was concluded that the hydrogen-bonding in the excited state, which leads to the twisting around the central CC bond and/or to the out-of-plane deformation, was of crucial importance in the rapid deactivation.