Triplet Sensitized Photolysis of a Vinyl Azide: Direct Detection of a Triplet Vinyl Azide and Nitrene

Photolysis of vinylazide 1, which has a built-in acetophenone
triplet sensitizer, in argon-saturated toluene results in azirine 2, whereas irradiation in oxygen-saturated toluene yields
cyanide derivatives 3 and 4. Laser flash
photolysis of azide 1 in argon-saturated acetonitrile
shows formation of vinylnitrene 1c, which has a λmax at ∼300 nm and a lifetime of ∼1 ms. Vinylnitrene 1c is formed with a rate constant of 4.25 × 105 s–1 from triplet 1,2-biradical 1b. Laser flash photolysis of 1 in oxygen-saturated acetonitrile
results in 1c-O (λmax = 430 nm, τ
≈ 420 μs acetonitrile). Density functional theory (DFT)
calculations were used to aid in the characterization of the intermediates
formed upon irradiation of azide 1 and to validate the
proposed mechanism for its photoreactivity.