In this research internal sensitization has been utilized to photochemically generate triplet alkyl nitrenes in solution and solid-state. Irradiating alkyl azides containing aryl ketone chromophores with light over 300 nm allows only the aryl ketone chromophore to be excited. The triplet aryl ketone chromophore created from excitation can then transfer triplet energy to the alkyl azide moiety, forming a triplet alkyl nitrene.
Solution irradiation allowed triplet alkyl nitrenes to be trapped in bimolecular reactions. In solution irradiations of Azides 1 the major solution photoproduct was found to be N-benzoyl benzamides derivatives formed by the trapping of a triplet alkyl nitrene with a benzoyl radical.
Photolysis of Azides 2 in solution was found to yield three products which can be attributed to bimolecular trapping of the triplet alkyl nitrene. The major photoproducts were identified as 1-phenyl-3-[5-phenylpyrazol-1-yl]-propan1-one derivatives, formed from dimerization of triplet alkyl nitrenes. The remaining photoproducts were found to be 3-(3-oxo-3-phenyl-propylamino)-1-phenyl-propenone derivatives and 3-(3-oxo-3-phenyl-propylamino)-1-phenyl-propan-1-one derivaitves formed from trapping of the triplet alkyl nitrene with propiophenone radicals.
When Azides 3 were irradiated in solution the products were found to form acetophenone derivatives and 5-(4-phenyl)-pyrrole derivatives created from 1,4 intramolecular hydrogen atom abstraction. Formation of the triplet alkyl nitrene lead to the creation of 5-(4- phenyl)-3,4-dihydro-2H-pyrrole derivatives.
Irradiations of alkyl azides within molecular crystals yielded interesting results. In solid state irradiations of Azides 1 the photoproduct was found to be N-methylene benzamide derivatives in all cases. This was interesting because the bimolecular reactivity observed in solution was changed to unimolecular reactivity within the restraints of a crystal lattice. Oxygen trapping studies indicate that the product is formed from α-cleavage of the triplet aryl ketone, followed by rearrangement of the resultant fragments.
In solid state photolysis of Azides 2 energy transfer from the aryl ketone to the alkyl azide moiety was found to create the triplet alky nitrene which underwent dimerizaion. It was found that the products of all solid-state irradiations can be correlated to the X-ray crystallography of the starting azide.