Photolysis of tert-butyl aroylperbenzoates (BAPs) 1-4 in benzene and acetonitrile at 335 or 267 nm produces the S 1 states (λ max ≈ 590 nm) that rapidly intersystem cross (k ISC ≈ 1.3 × 10 11 s -1 ) into the triplet states (λ max ≈ 560 nm, τ T ) 0.6-0.7 ns in benzene). Results from the 267 nm excitation experiments of 1 in acetonitrile suggest the rate of the S 2 f S 1 internal conversion (k S 2 fS 1 ) 1.6 × 10 12 s -1 ) is similar to that of benzophenone and p-iodobenzophenone. The rate of the S 1 f T 1 intersystem crossing is not affected by the solvent or the excitation wavelength. However, decay of the triplet states of 1 and p-iodobenzophenone is faster in acetonitrile than in benzene. Intramolecular triplet energy dissipation to a repulsive excited triplet state of the O-O bond of BAPs may be a possible mechanism. The results obtained from semiempirical and ab initio calculations have been presented.
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