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Updated: Aug 30, 2025

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional π-conjugate Systems
Published on: February 10, 2020
Ultrafast Dynamics of a Molecular Switch from Resonance Raman Spectroscopy: Comparing Visible and UV Excitation
Kristen H Burns1, Christopher G Elles1
1Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States.
Abstract:
Resonance Raman spectroscopy probes the ultrafast dynamics of a diarylethene (DAE) molecular switch following excitation into the first two optical absorption bands. Mode-specific resonance enhancements for Raman excitation at visible (750-560 nm) and near-UV (420-390 nm) wavelengths compared with the calculated and experimental off-resonance Raman spectrum at 785 nm reveal different Franck-Condon active vibrations for the two electronically excited states. The resonance enhancements at visible wavelengths are consistent with initial motion on the first excited-state that promotes the cycloreversion reaction, whereas the enhancements for excitation at near-UV wavelengths highlight motions involving conjugated backbone and phenyl ring stretching modes that are orthogonal to the reaction coordinate. The results support a mechanism involving rapid internal conversion from the higher-lying state followed by cycloreversion on the first excited state. These observations provide new information about the reactivity of DAE derivatives following excitation in the visible and near-UV.
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