Typically, in photoinduced PCET processes, a photocatalyst initiates electron transfer, while an external hydrogen bond donor facilitates proton transfer. However, in 2019, Collins and co-workers developed a novel bifunctional diamine diphosphine copper(I) complex, [Cu(pypzs)(BINAP)]BF4 (21.2), which, under blue LEDs, promoted the reductive pinacol coupling of ketones through PCET without an external hydrogen bond donor (Figure ). Remarkably, the sulfonamide moiety of the pyrazole-pyridine-based ligand pypzs (5-(4-fluorosulfonyl)amino-3-(2-pyridyl)-pyrazole) in the copper complex facilitated successful hydrogen bond donation despite its significantly lower relative acidity compared to dppa, a potent hydrogen bond donor for PCET, which can be attributed to the increased proximity of the substrate to the photoactive complex. The pypzs ligand also sufficiently enhanced the excited state lifetime of the catalyst (τ = 8.95 ns), further establishing its suitability for the transformation. Under optimized reaction conditions, various aldehydes and ketones underwent successful reductive pinacol-type coupling (Figure ). The authors proposed a plausible mechanism wherein the Hantzsch ester reductively quenches the excited state then interacts with the ketone or aldehyde substrate, followed by a simultaneous PCET to generate the ketyl This radical subsequently adds to another ketone or aldehyde, resulting in the formation of reductively coupled 1,2-diols (Figure ).