Recent Advances on Diarylethene-Based Photoswitching Materials: Applications in Bioimaging, Controlled Singlet Oxygen Generation for Photodynamic Therapy and Catalysis.

Photoswitching materials have emerged as a promising class of compounds that possess manifold interesting properties rendering their widespread use from photoswitches, regulators to optoelectronic devices, security technologies and biochemical assays. Diarylethenes (DAE) constitute one such category of photoswitchable compounds, where the key features of stability, photoisomerization wavelengths, quantum yield and variability in the photoisomers significantly depend on their derivatization. The last decade has witnessed a surge in the engagement of DAEs in different areas of chemical and biological sciences, like biomarkers, controlled generation of singlet oxygen, photo-dynamic therapy, chemosensing, catalysis, etc. In all the cases, the photoswitchability of DAE is the principal regulating factor along with its emission properties according to the appended groups. Previous reviews on applications of DAE-based systems did not predominantly cover all the aspects of biological and industrial implementations. They have covered only one field of application either in the biological science or in the synthetic aspect or photochromic aspects only. This review is a coalition of all those aspects in last six years. Here the variation of properties of the DAE systems with respect to structural diversifications have been discussed in detail along with their potential applications in bioimaging of cells, regulating singlet oxygen generation for photodynamic therapy and catalysis of organic reactions, and their future prospects. A tabular presentation of the photophysical properties of DAE derivatives adds to the basic understanding of this subject at a glance. We hope that this cumulative collection of contemporary research on DAE, as presented in this review, will enhance the knowledge of the readers about synthetic design anticipating their properties well in advance, and will certainly motivate researchers to generate new DAE architectures with superior chemical and biological properties in future.