Sequence-independent activation of photocycloadditions using two colours of light.

We exploit two reactive chromophores to establish sequence-independent photochemical activation, employing -methyl benzaldehyde (MBA) and ,-(dimethylamino)pyrene aryl tetrazole (APAT) with -(2-hydroxy)ethyl maleimide (HEM), without any additives. Critically, the order of the irradiation sequence is irrelevant, as the shorter wavelength does not activate the higher wavelength activated species. Therefore, full sequence-independent λ-orthogonality is achieved through differences in both the reaction quantum yields ( and ) and wavelength-dependent reactivity profiles of the employed chromophores.