Simultaneous resonance Raman optical activity involving two electronic states

Area of Science:

• Chiroptical spectroscopy
• Vibrational spectroscopy
• Computational chemistry

Background:

• Resonance Raman optical activity (RROA) is a powerful technique for probing chiral molecules.
• Previous RROA studies primarily focused on single-electronic-state (SES) models.
• Understanding RROA involving multiple electronic states is crucial for complex molecular systems.

Purpose of the Study:

• To report the first observation of strong RROA involving more than one resonant electronic state.
• To investigate the RROA of the chiral transition metal complex bis-(trifluoroacetylcamphorato) copper(II) (Cu(tfc)(2)).
• To extend RROA theory to a two-electronic-state (TES) model for spectral interpretation.

Main Methods:

• Experimental measurement of Resonance Raman (RR) and RROA spectra of Cu(tfc)(2) using 532 nm laser excitation.
• Vibrational assignments using non-RR spectra (1024 nm excitation) compared with Density Functional Theory (DFT) calculations.
• Theoretical extension of SES-RROA theory to a TES model.
• Analysis of UV-vis electronic absorbance spectra and Time-Dependent DFT (TD-DFT) calculations.

Main Results:

• Strong RROA signals were observed for Cu(tfc)(2) at 532 nm excitation, indicating multi-state involvement.
• Vibrational assignments were successfully made by correlating experimental data with DFT calculations.
• A TES model was developed and applied to interpret the observed RROA spectra.
• Specific electronic states responsible for the RROA were identified using UV-vis and TD-DFT data.

Conclusions:

• The study presents the first experimental evidence of strong RROA arising from two resonant electronic states.
• The developed TES-RROA theory provides a framework for interpreting complex RROA spectra.
• This work expands the application of RROA spectroscopy to systems with multiple electronic transitions.