Time-resolved EPR revealed C(sp 3 )-H activation through a photo-enhanced phthalimide- N -oxyl (PINO) radical.

The time-resolved electron paramagnetic resonance (EPR) technique under photochemical conditions as an efficient strategy to investigate the fast formation of abundant long-lived PINO radicals ( = 204 s) and their activation of the C(sp)-H process has been researched. This developed method offers a pathway for investigating the properties and tracking the transformations of radical species in the photoredox reaction process.