Photolysis of tert-butyl aroylperbenzoates (BAPs) 1-4 in benzene and acetonitrile at 335 or 267 nm produces the S-1 states (lambda(max) approximate to 5 590 nm) that rapidly intersystem cross (k(ISC) approximate to 1.3 x 10(11) s(-1)) into the triplet states (lambda(max) approximate to 560 nm, tau(T) = 0.6-0.7 ns in benzene). Results from the 267 nm excitation experiments of I in acetonitrile suggest the rate of the S-2 --> S-1 internal conversion (k(S2-->S1) = 1.6 x 10(12) s(-1)) is similar to that of benzophenone and p-iodobenzophenone. The rate of the S-1 --> T-1 intersystem crossing is not affected by the solvent or the excitation wavelength. However, decay of the triplet states of I 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.