Solvent Environment Revealed by Positively Chirped Pulses

Area of Science:

• Physical Chemistry
• Spectroscopy
• Biomolecular Dynamics

Background:

• Investigating the early time response of molecules and solvents in solution is challenging.
• Distinguishing inter- and intramolecular contributions to electronic and vibrational dynamics is complex.
• Time-resolved and frequency-resolved spectroscopic techniques are crucial for studying molecular behavior.

Purpose of the Study:

• To explore the early solvation dynamics of large organic molecules and biomolecules in solution.
• To assess the utility of chirped laser pulses as probes for solvent-viscosity effects.
• To compare the fluorescence and stimulated emission yields of laser dyes IR144 and IR125 under varying chirp conditions.

Main Methods:

• Employed time-resolved and frequency-resolved spectroscopy.
• Utilized chirped laser pulses (positive and negative chirp) to excite and probe laser dyes IR144 and IR125.
• Measured fluorescence and stimulated emission yields as a function of pulse chirp and duration.

Main Results:

• Positively chirped pulses demonstrated unique sensitivity to solvent viscosity, unlike negatively chirped pulses.
• The fluorescence maximum for IR125 occurred near transform-limited pulses.
• For IR144, the fluorescence maximum shifted to positively chirped pulses stretched to hundreds of femtoseconds, indicating sensitivity to solvation dynamics.

Conclusions:

• Chirped pulse spectroscopy provides a straightforward, one-beam method for probing early solvation dynamics.
• The sensitivity of positively chirped pulses to solvent viscosity offers a new avenue for studying molecular-environment interactions.
• This technique is valuable for understanding the complex dynamics of large organic molecules and biomolecules in solution.