Femtosecond time-resolved solvation process of a solution: Constraints of vibrational degrees of freedom in the supercooled state

Femtosecond time-resolved fluorescence spectra have been measured for a dye solution from 170 to 296 K. The time evolution of the spectra shows that there are three energy relaxation components of about 0.1 ps, a few ps and a time constant changing from 10 ps to 1 ns with decreasing temperature. It is considered from the temperature dependence of the relaxation process that a part of the solvation process responsible for the two fast components slows down because vibration-like degrees of freedom are constrained under strong hydrogen-bonded networks near the supercooled state.