UV-vis absorption studies of singlet to triplet intersystem crossing rates of aromatic ketones: effects of molecular geometry

The effect of the molecular geometry of diaryl and arylalky ketones on the rate of intersystem crossing (ISC) was investigated by employing picosecond pump—probe studies of the growth of triplet—triplet absorptions at 532 and 355 nm. Vibrational relaxation within the triplet manifold was found to interfere with measurement of the ISC rates for certain benzophenone derivatives. The observed rapid decay of absorption at 355 nm is attributed to relaxation of vibrationally excited triplets. The trends observed are consistent with direct singlet-to-triplet ISC from S2 to T1