Phenomenon to functions: Photochromism of diarylpyrans, spectrokinetic properties and functional materials

Diarylbenzo- and naphthopyrans are one of the important and well-known classses of organic photochromic systems. Their photolysis leads to highly colored o-quinonoid intermediates. The mechanistic details and spectrokinectic properties of the photogenerated colored intermediates have been extensively studied. Accordingly, stereoelectronic effects have been shown to play a crucial role in controlling properties such as spectrokinetics, fatigue resistance and colorability. Much research continues unabated to develop photochromic materials with properties that surpass the existing ones for application in ophthalmic lenses as well as optical data storage devices. In the realm of materials chemistry, the diarylpyran unit is presently exploited as an essential design element to produce functional materials. Given the facile synthetic access to molecular systems that respond to light as an external stimulus leading to widely distinct physicochemical properties, we believe that more exciting research based on diarylpyran photochemistry will germinate in materials chemistry and biology in the near future. This review with a coverage of the phenomenon since its inception to the present state of application for functional materials–through synthesis and mechanistic details–should serve as an invaluable resource to an uninhibited chemist to exploit the photochromism of diarylpyrans for diverse functions/applications.