Vibrational Circular Dichroism Spectroscopy of Chiral Molecular Crystals: Insights from Theory

Abstract

Chirality is a curious phenomenon that appears in various forms. While the concept of molecular (RS‐)chirality is ubiquitous in chemistry, there are also more intricate forms of structural chirality. One of them is the enantiomorphism of crystals, especially molecular crystals, that describes the lack of mirror symmetry in the unit cell. Its relation to molecular chirality is not obvious, but still an open question, which can be addressed with chiroptical tools. Vibrational circular dichroism (VCD) denotes chiral infrared (IR) spectroscopy that is susceptible to both, the molecular as well as the intermolecular space by means of vibrational transitions. When carried out in the solid state, VCD delivers a very rich set of non‐local contributions that are determined by crystal packing and collective motion. Since its discovery in the 1970s, VCD has become the method of choice for the determination of absolute configurations, but its applicability reaches beyond towards the study of different crystal forms and polymorphism. This brief review summarises the theoretical concepts of crystal chirality and how computations of solid‐state VCD can shed light into the intimate connection of chiral structure and vibrational optical activity.

Optical Phenomena in Molecule-Based Magnetic Materials

“…918,975,989 On the other hand, vibrational CD (VCD) spectroscopy working in the NIR regime is a complemental tool for investigating chirality, e.g., residing in organic ligands. 899,990,991 Circular dichroism can be alternatively induced by magnetization, and the related effect is called magnetic circular dichroism (MCD). 992,993 Owing to its dependence on the magnetization of the medium, MCD provides a useful spectroscopic tool to study the magnetic anisotropy and other magnetic features of molecule-based materials, including molecular nanomagnets.…”

“…The NOA of chiral materials can be characterized by natural CD (NCD) spectroscopy, and the optical resolution between two enantiomers can be evidenced by opposite Cotton effects in the respective CD spectra. ,, Electronic CD (ECD) spectroscopy working in the UV–vis region is commonly utilized for characterizing chiral materials, including chiral molecule-based magnetic materials, showing pronounced electronic absorption transitions. It is a particularly useful optical method to probe if the chirality is transferred from peripheral chiral groups to the main chromophores. ,, On the other hand, vibrational CD (VCD) spectroscopy working in the NIR regime is a complemental tool for investigating chirality, e.g., residing in organic ligands. ,, …”

Harmonic scale factors of fundamental transitions for dispersion-corrected quantum chemical methods

“…[1] This spectroscopic technique observes intra-and intermolecular vibrational motions, as their resonant excitation energies lie in the IR region, i.e., approximately from 100 to 10 4 cm −1 (wavelengths from 0.1 mm to 780 nm). [1,2] In addition to simple absorption/emission IR spectroscopy, [3] there are other techniques, such as vibrational circular dichroism (VCD), which is sensitive to molecular chirality, [4,5] vibrational Raman spectroscopy, [6] inelastic neutron scattering (INS), [6][7][8] infrared/ultraviolet (IR-UV) ion dip spectroscopy, [9] infrared multiple photon dissociation (IRMPD) spectroscopy, [10][11][12][13][14] various messenger-tagging methods (such as helium, nitrogen, or hydrogen molecular tag), [15][16][17][18][19][20] that allow measuring spectra of ions, and vibrational sum frequency generation (VSFG) spectroscopy, that allows to probe molecular motions at the phase interfaces. [21,22] All these vibrational spectroscopy methods allow us to inspect the properties of molecules, ions, and molecular aggregates in the gas, liquid, and solid phases and at the interfaces between phases.…”

“…Despite the existence of various vibrational diagnostic bands for molecular functional groups [11,12,27] and databases of the experimental IR spectra, such as the NIST Chemistry WebBook, [28] most experimental studies of novel uncharacterized substances have to rely on quantum-chemical calculations. [5,6,8,9,[16][17][18][29][30][31][32][33] To achieve a sufficiently good agreement of quantumchemical calculations and experiment requires the application of expensive computational methods and direct inclusion of anharmonic effects. [6,8,34,35] Unfortunately, such anharmonic calculations require significant expertise and computational efforts, which make them unfeasible for many practical cases.…”

Controllable Chiral Lattices for 2D ROA Mapping and a Long-term Stable Broadband CPL Detector

“…possessing a broadband optical activity from visible to IR signi cantly increases due to their intrinsic anisotropy in both inter-and intra-band transitions [12][13][14] . One signi cant condition is that the crystals have to have one-handedness, left or right.…”