Manufacturing chemicals with light: any role in the circular economy?

We outline how recent developments in photochemistry can contribute to the realization of the 1912 vision of the pioneering Italian scientist Giacomo Ciamician, namely world-wide chemical-using industry-based chemical plants fuelled solely by the Sun. We then show how a combination of organic photochemistry and flow chemistry could contribute to the circular economy by harnessing the ability of light to provide the energy to promote reactions without the need for some of the added reagents that are necessary in more traditional chemical routes, so-called 'reagentless' chemistry. Photochemistry has a long history but recently it has undergone a renaissance, particularly with the rise in interest in photoredox chemistry. Continuous photoreactors offer a route to scaling up such reactions to a productivity needed for smaller scale pharmaceutical manufacture. We describe some reactor designs from our own laboratory and outline some of their applications. We then relate these to the requirements of the circular economy and the need to conserve the stocks of the less abundant chemical elements. This article is part of a discussion meeting issue 'Science to enable the circular economy'.