Benchmarking the Calculated Resonance Raman Spectrum of a Diarylethene-Based Molecular Switch Using the Gradient...

Area of Science:

• * Molecular Spectroscopy
• * Computational Chemistry
• * Photochemistry

Background:

• * Resonance Raman spectroscopy offers insights into molecular dynamics post-optical excitation.
• * Vibrational frequencies indicate ground-state structure, while band intensities reflect excited-state dynamics.
• * Accurate assignment of experimental spectra often necessitates computational methods.

Purpose of the Study:

• * To evaluate methods for calculating resonance Raman intensities.
• * To compare the Franck-Condon and gradient approximation methods for resonance Raman spectroscopy.
• * To assign vibrational modes involved in the excited-state dynamics of a diarylethene molecular switch.

Main Methods:

• * Experimental measurement of on- and off-resonance Raman spectra.
• * Computational simulation using off-resonance, Franck-Condon, and gradient approximation methods.
• * Analysis of a diarylethene-based molecular switch with 129 normal modes.

Main Results:

• * Off-resonance calculations provide accurate frequencies but not intensities.
• * Including resonance-enhancement effects is vital for correct vibrational mode assignment.
• * The gradient approximation method yields results in good agreement with experimental resonance Raman spectra.
• * The gradient approximation avoids the computational cost of excited-state geometry optimization.

Conclusions:

• * The gradient approximation is a reliable method for simulating resonance Raman spectra.
• * Accurate mode assignments reveal key stretching motions in the excited-state dynamics of the molecular switch.
• * Computational methods incorporating resonance effects are essential for understanding molecular photodynamics.