1 Solvent Environment Revealed 2 by Positively Chirped Pulses

4 Abstract The spectroscopy of large organic molecules and biomolecules in 5 solution has been investigated using various time-resolved and frequency-resolved 6 techniques. Of particular interest is the early response of the molecule and the 7 solvent, which is difficult to study due to the ambiguity in assigning and differ-8 entiating inter- and intra-molecular contributions to the electronic and vibrational 9 populations and coherence. Our measurements compare the yield of fluorescence 10 for two laser dyes IR144 and IR125 as a function of chirp. While negatively chirped 11 pulses are insensitive to solvent viscosity, positively chirped pulses are found to be 12 uniquely sensitive probes of solvent viscosity. 13 1