The switch-off method: rapid investigation of flow photochemical reactions

In a flow photochemical process switching off the light source and monitoring the reaction composition as it leaves the photoreactor allows the effect of all irradiation times up to a maximum to be analysed in a single experiment. The switch-off method was illustrated using three reactions: [2 + 2] intermolecular photocycloadditions between an alkene and alkyne, and between two alkenes, and a Mallory photocyclization of cis -stilbene. The 'Switch-Off' method for rapid investigation of flow photochemical reactions was developed and three model reactions were investigated. Full photoreaction profiles were obtained with exposure times from maximum down to zero.