Recognition of the True and False Resonance Raman Optical Activity

Ewa Machalska,Tadeusz Andruniów,Dorota Gryko,Aleksandra J Wierzba,Petr Bouř,Grzegorz Zajac,Malgorzata Baranska,Maciej Spiegel,Josef Kapitán

doi:10.1002/ange.202107600

Abstract

AbstractResonance Raman optical activity (RROA) possesses all aspects of a sensitive tool for molecular detection, but its measurement remains challenging. We demonstrate that reliable recording of RROA of chiral colorful compounds is possible, but only after considering the effect of the electronic circular dichroism (ECD) on the ROA spectra induced by the dissolved chiral compound. We show RROA for a number of model vitamin B12derivatives that are chemically similar but exhibit distinctively different spectroscopic behavior. The ECD/ROA effect is proportional to the concentration and dependent on the optical pathlength of the light propagating through the sample. It can severely alter relative band intensities and signs in the natural RROA spectra. The spectra analyses are supported by computational modeling based on density functional theory. Neglecting the ECD effect during ROA measurement can lead to misinterpretation of the recorded spectra and erroneous conclusions about the molecular structure.

Highlights

Resonance Raman optical activity (RROA) possesses all aspects of a sensitive tool for molecular detection, but its measurement remains challenging
In the present study, we show that the measured ROA of chiral colorful compounds is a sum of the true RROA and the electronic circular dichroism (ECD)-induced parts (ROAECD): RROA 1⁄4 RROAtrue þ ROAECD
Where IR and IL are intensities of right- and left-circular polarized luminescence (CPL) detected by the ROA/Raman spectrometer; De and De’ are decadic absorption coefficients (ECD intensities) at the incident and scattered light frequency, respectively, DOC is the degree of circularity characteristic for each vibration, and c is concentration of the compound that exhibits the ROAECD effect

Summary

Introduction

Resonance Raman optical activity (RROA) possesses all aspects of a sensitive tool for molecular detection, but its measurement remains challenging. Intrigued by the ECD/ROA interference, we envisaged that it would be significant for the solvent spectra and for chiral, light-absorbing solutes. Where IR and IL are intensities of right- and left-CPL detected by the ROA/Raman spectrometer; De and De’ are decadic absorption coefficients (ECD intensities) at the incident and scattered light frequency, respectively, DOC is the degree of circularity characteristic for each vibration, and c is concentration of the compound that exhibits the ROAECD effect.

Results

Conclusion