In this research two major types of photoreactivities have been investigated. The first one the photoreactivity of the triplet vinyl nitrene, which is considerably stable. We have successfully utilized two ways to form the triplet vinyl nitrene by photolyzing 2H-Azirines and vinyl azides. We also studied the photoreactivity of alkyl azides containing the triplet sensitization chromophores both in solution and solid state. We are interested in the solid reactivity as the constraints in the solid state can affect on the movement of the molecules.
Photolysis of 3-Phenyl-2-Methyl-2H-Azirine in dichloromethane yields benzaldehyde and 1-chloro-1-phenylpropan-2-one. Similarly, photolysis of 3-Phenyl-2-Methyl-2H-Azirine in bromoform yields benzaldehyde and 1-bromo-1-phenylpropan-2-one. However, photolysis of 2-Phenyl-3-Methyl-2H-Azirine in acetonitrile yields two dimers exo-2,6-dimethyl-4,5-diphenyl-1,3-diazabicyclo[3.1.0]hex-3-ene and endo-2,6-dimethyl-4,5-diphenyl-l,3-diazabicyclo-[3.1.0]hex-3-ene. Laser flash photolysis of 3-Phenyl-2-Methyl-2H-Azirine in acetonitrile results in a transient absorption with ?max at ~440 nm due to the formation of triplet azirine and triplet vinyl nitrene, respectively. In comparison, laser flash photolysis of 2-Phenyl-3-Methyl-2H-Azirine in acetonitrile shows a transient absorption with maximum at 320 nm due to the formation of ylide, which has a lifetime of 13 ms. Photolysis of 2-Phenyl-3-Methyl-2H-Azirine in cryogenic argon matrices results in the formation of ylide.
Photolysis of (E)-3-azido-1-(4-chlorophenyl)prop-2-en-1-one in argon-saturated and oxygen-saturated CDCl 3; solution yielded (2H-azirin-2-yl)(4-chlorophenyl)methanone, 3-(4-chlorophenyl)-3-oxopropanenitrile and 5-(4-chlorophenyl)isoxazole as the photoproducts. Upon further photolysis, the proton NMR shows decompositions of (2H-azirin-2-yl)(4-chlorophenyl)methanone and 5-(4-chlorophenyl)isoxazole to form 3-(4-chlorophenyl)-3-oxopropanenitrile. Laser flash photolysis of (E)-3-azido-1-(4-chlorophenyl)prop-2-en-1-one in acetonitrile produced transient spectrum with λ max at ~360 nm, which we assign to triplet vinylnitrene. The kinetic study shows the lifetime of triplet vinylnitrene in argon-saturated acetonitrile is 17 µs. In comparison, transient spectra of triplet vinylnitrene in nanocrystals while the lifetime of triplet vinylnitrene in solid-state is elongated to be 42 µs. The crystal lattices stabilize triplet vinylnitrene and thus it is possible to use crystal lattices to render triplet vinylnitrenes stable and use their high spin property to make stable organic magnetic materials.
We investigated the photoreactivity of alkyl azides 5-azido-1-(4-methoxyphenyl)pentan-1-one and 6-azido-1-(4-methoxyphenyl)hexan-1-one. We used product studies, phosphorescence, laser flash photolysis (LFP, 308 nm, 17 ns) and theoretical DFT calculations to identify the intermediates formed by irradiating 5-azido-1-(4-methoxyphenyl)pentan-1-one and 6-azido-1-(4-methoxyphenyl)hexan-1-one. Laser flash photolysis of azide 5-azido-1-(4-methoxyphenyl)pentan-1-one and 6-azido-1-(4-methoxyphenyl)hexan-1-one yielded the triplet ketone which then transfers energy to the azido group causing the loss of a molecule of nitrogen to form the triplet nitrenes. The solid state LFP shows the lifetimes of the triplet ketone and the triplet nitrene in solid state are longer than in the solution.