Insights into the Role of Graphitic Carbon Nitride as a Photobase in Proton-Coupled Electron Transfer in (sp3)C-H Oxygenation of Oxazolidinones

Graphitic carbon nitride (g-CN) is a transition metal free semiconductor that mediates a variety of photocatalytic reactions. Although photoinduced electron transfer is often postulated in the mechanism, proton-coupled electron transfer (PCET) is more favorable pathway for substrates possessing X-H bonds. Upon excitation of an (sp2)N-rich structure of g-CN with visible light, it behaves as a photobase - undergoes reductive quenching accompanied by abstraction of a proton from a substrate. The results of modelling allowed us to identify active sites for PCET - the 'triangular pockets' on the edge facets of g-CN. We employ excited state PCET  from the substrate to g-CN to cleave selectively endo-(sp3)C-H bond in oxazolidine-2-ones followed by trapping the radical with O2. This reaction affords 1,3-oxazolidine-2,4-diones. Measurement of apparent pKa value and modeling suggest that g-CN excited state can cleave X-H bonds that are characterized by bond dissociation free energy (BDFE) ~100 kcal mol-1.

Progress in Development of Photocatalytic Processes for Synthesis of Fuels and Organic Compounds under Outdoor Solar Light

With photovoltaics becoming a mature, commercially feasible technology, society is willing to allocate resources for developing and deploying new technologies based on using solar light. Analysis of projects supported by the European Commission in the past decade indicates exponential growth of funding to photocatalytic (PC) and photoelectrocatalytic (PEC) technologies that aim either at technology readiness levels (TRLs) TRL 1-3 or TRL > 3, with more than 75 Mio€ allocated from the year 2019 onward. This review provides a summary of PC and PEC processes for the synthesis of bulk commodities such as solvents and fuels, as well as chemicals for niche applications. An overview of photoreactors for photocatalysis on a larger scale is provided. The review rounds off with the summary of reactions performed at lab scale under natural outdoor solar light to illustrate conceptual opportunities offered by solar-driven chemistry beyond the reduction of CO₂ and water splitting. The authors offer their vision of the impact of this area of research on society and the economy.