Estimating the time-zero spectrum in time-resolved emmsion measurements of solvation dynamics

We describe a simple method for determining the position of the time-zero spectrum in time-resolved emission studies of solvation dynamics. The method uses only steady-state spectral data and therefore provides an independent means of establishing the origin of the solvation response that is not limited by the time resolution the apparatus used to measure the dynamics. We show that the three typical solvatochromic probes, coumarins 102 and 153, and 4-aminophthalimide, the method predicts the frequency of the t=0 spectrum to an accuracy of better than± 200 cm ^-, or to better than ± 10% of the total spectral shift observed with these probes in high-polarity solvents. A secondary result of these studies is the ubiquitous observation of sub-10 ps components (≈ 20% amplitude) in the solvation response of propanol and glycerol, even under conditions where the average solvation time is in the nanosecond range.