PHOTOINDUCED TRANSIENT PHENOMENA IN CYCLODEXTRIN SOLID COMPLEXES - PHOTOCHEMISTRY OF AROMATIC KETONES

The photochemistry of benzophenone (BP) in cyclodextrin (alpha-, beta- and gamma-CD) solid complexes has been examined by time-resolved diffuse reflectance laser-flash photolysis techniques. Benzophenone is photoreduced as a consequence of hydrogen abstraction from the CD cavity. Both BP phosphorescence and diphenylketyl radical fluorescence spectra in CD solid complexes were recorded at room temperature. Lifetime distribution analysis is used in order to describe the dynamics of triplet decay. The most probable BP triplet lifetime is found to decrease as the size of the CD cavity decreases (alpha-CD = 0.3 mu s, beta-CD = 0.5 mu s and gamma-CD = 1.2 mu s). This observation contrasts with that for xanthone, a more rigid, yet structurally related ketone (alpha-CD = 8 mu s, beta-CD = 3 mu s and gamma-CD = 0.6 mu s) studied previously. The differences are interpreted in terms of changes in triplet reactivity and of restrictions on molecular mobility.