Raman optical activity (ROA) is commonly measured with green light (532 nm) excitation. At this wavelength, however, Raman scattering of europium complexes is masked by circularly polarized luminescence (CPL). This can be avoided using near-infrared (near-IR, 785 nm) laser excitation, as demonstrated here by Raman and ROA spectra of three chiral europium complexes derived from camphor. Since luminescence is strongly suppressed, many vibrational bands can be detected. They carry a wealth of structural information about the ligand and the metal core, and can be interpreted based on density functional theory (DFT) simulations of the spectra. For example, jointly with ROA experimental data, the simulations make it possible to determine absolute configuration of chiral lanthanide compounds in solution.

• Klíčová slova
• Raman optical activity, chiral lanthanide complexes, circularly polarized luminescence, density functional theory, spectra simulations,
• Publikační typ
• časopisecké články MeSH

The broader availability of cost-effective methodologies like second-order vibrational perturbational theory (VPT2), also in general-purpose quantum chemical programs, has made the inclusion of anharmonic effects in vibrational calculations easier, paving the way to more accurate simulations. Combined with modern computing hardware, VPT2 can be used on relatively complex molecular systems with dozen of atoms. However, the problem of resonances and their corrections remains a critical pitfall of perturbative methods. Recent works have highlighted the sensitivity of band intensities to even subtle resonance effects, underlying the importance of a correct treatment to predict accurate spectral bandshapes. This aspect is even more critical with chiroptical spectroscopies whose signal is weak. This has motivated the present work in exploring robust methods and criteria to identify resonances not only in energy calculations but also on the transition moments. To study their performance, three molecules of representative sizes ranging from ten to several dozens of atoms were chosen. The impact of resonances, as well as the accuracy achievable once they are properly treated, is illustrated by the changes in spectral bandshapes, including chiroptical spectroscopies.

• Publikační typ
• časopisecké články MeSH

Combining Raman scattering and Raman optical activity (ROA) with computer simulations reveals fine structural and physicochemical properties of chiral molecules. Traditionally, the region of interest comprised fundamental transitions within 200-1800 cm-1. Only recently, nonfundamental bands could be observed as well. However, theoretical tools able to match the observed spectral features and thus assist their assignment are rather scarce. In this work, we present an accurate and simple protocol based on a three-quanta anharmonic perturbative approach that is fully fit to interpret the observed signals of methyloxirane within 150-4500 cm-1. An unprecedented agreement even for the low-intensity combination and overtone transitions has been achieved, showing that anharmonic Raman and ROA spectroscopies can be valuable tools to understand vibrations of chiral molecules or to calibrate computational models.

• Publikační typ
• časopisecké články MeSH