Excited-state hydrogen bond strengthening of coumarin 153 in ethanol solvent: a TDDFT study

So far, coumarin dyes have been extensively studied with various means to understand their photophysical behaviors and photochemical properties. Here, our performing time-dependent density functional theory calculation is aimed at exploring the excited-state hydrogen bonding dynamics of coumarin 153 (C153) in protic ethanol (EtOH) solvent. The calculated results suggest that the excited-state hydrogen bond C = O center dot center dot center dot H-O between C = O group and O-H group in the C153-EtOH complex is strengthened, and the S-0 -> S-1 transition of the complex corresponds to the highest occupied molecular orbital (HOMO) hopping to the lowest unoccupied molecular orbital (LUMO). The excited-state hydrogen bond strengthening has been further confirmed by its larger binding energy in the S-1 state than in the S-0 state. In addition, because of the formation of the hydrogen bond C = O center dot center dot center dot H-O, a red shift of about 7 nm occurs in the electronic spectra of the C153-EtOH complex, which is in good accordance with the experiment result. Copyright (C) 2016 John Wiley & Sons, Ltd.