Hydrogen-bond dynamics in the excited state of coumarin 102-aniline hydrogen-bonded complex

Comparison of the steady-state FTIR absorption spectra of coumarin-102 (C-102) in tetrachloroethylene with added aniline of various concentrations, in neat aniline and in neat N,N-dimethylaniline (DMA), indicates formation of a hydrogen-bonded complex between C-102 and aniline in solution. Subpicosecond time-resolved infrared absorption spectroscopy has been applied to study the dynamics of the hydrogen-bond following photoexcitation of C-102 chromophore in a C-102−aniline hydrogen-bonded complex. Upon photoexcitation at 400 nm, the hydrogen bond between C-102 and aniline breaks within 250 fs. Reformation of hydrogen-bond between the excited C-102 molecule and aniline takes place within about 30 ps. Biexponential temporal dynamics monitored at CO stretching vibration (1736−1742 cm-1) in neat aniline, which is a strongly structured solvent due to formation of intermolecular hydrogen bonds, reveals the biphasic solvation dynamics of aniline with solvation times 0.6 and 7.2 ps. These time constants have been...