Visible light photocatalysis as a greener approach to photochemical synthesis

Sunlight is potentially an ideal green 'reagent' for chemical synthesis, but poor absorption by organic substrates makes direct solar photochemistry generally inefficient. Here, recent progress in the use of the simple organometallic complexes to harness the power of the sun is summarized, and prospects for the future of this exciting field highlighted. Light can be considered an ideal reagent for environmentally friendly, 'green' chemical synthesis; unlike many conventional reagents, light is non-toxic, generates no waste, and can be obtained from renewable sources. Nevertheless, the need for high-energy ultraviolet radiation in most organic photochemical processes has limited both the practicality and environmental benefits of photochemical synthesis on industrially relevant scales. This Perspective describes recent approaches to the use of metal polypyridyl photocatalysts in synthetic organic transformations. Given the remarkable photophysical properties of these complexes, these new transformations, which use Ru(bpy)32+ and related photocatalysts, can be conducted using almost any source of visible light, including both store-bought fluorescent light bulbs and ambient sunlight. Transition metal photocatalysis thus represents a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.