Terahertz Fingerprints of Short-Range Correlations of Disordered Atoms in Diflunisal

Investigating the function and design of molecular materials through terahertz vibrational spectroscopy

Terahertz spectroscopy has proved to be an essential tool for the study of condensed phase materials. Terahertz spectroscopy probes the low-frequency vibrational dynamics of atoms and molecules, usually in the condensed phase. These nuclear dynamics, which typically involve displacements of entire molecules, have been linked to bulk phenomena ranging from phase transformations to semiconducting efficiency. The terahertz region of the electromagnetic spectrum has historically been referred to as the 'terahertz gap', but this is a misnomer, as there exist a multitude of methods for accessing terahertz frequencies, and now there are cost-effective instruments that have made terahertz studies much more user-friendly. This Review highlights some of the most exciting applications of terahertz vibrational spectroscopy so far, and provides an in-depth overview of the methods of this technique and its utility to the study of the chemical sciences.

Cooperative Photochemical Reaction Kinetics in Organic Molecular Crystals

Photoreactive molecular crystals have been intensively investigated as next-generation functional materials. Changes in physicochemical properties are usually interpreted in terms of static pre- and post-reaction molecular structures and packings determined by X-ray structure analysis. However, to elucidate the dynamic properties, it is necessary to understand the dynamic nature of photochemical kinetics in crystals. Reaction dynamics in the crystal phase can be dramatically different from those in dilute solution because the local molecular environment evolves as the surrounding reactant molecules are transformed into products. In this Review article, we summarize multiple examples of photochemical reactions in the crystalline phase that do not follow classical kinetic behavior. We also discuss different theoretical methods that can be used to describe this behavior. This Review article should help provide a foundation for future workers to understand and analyze photochemical reaction kinetics in crystals.