The Triplet State of a N-Phenylphthalimidine with High Intersystem Crossing Efficiency: Characterization by Transient Absorption Spectroscopy and DNA Sensitization Properties

The detailed triplet state characteristics of 2-(4-acetylphenyl)isoindolin-1-one (kINP), a N -phenylphthalimidine (PPI) derivative, have been studied in fluid solution at room temperature. The attachment of an acetyl group to the N -phenyl moiety of PPI has permitted to enhance the intersystem crossing quantum yield, generally low for such compounds. Upon 308-nm laser flash photolysis of kINP in acetonitrile, a triplet−triplet transition has been evidenced (λ max = 440 nm). Further characterization of this transient at 440 nm gave a lifetime τ = 11 μs, a molar absorption coefficient ε = 22 000 M -1 × cm -1, and an intersystem crossing quantum yield of 0.89. Moreover, a ππ* nature has been found for this triplet state that lies at ca. 290 kJ × mol -1 above the ground state. In addition to providing fundamental information on the triplet state properties of PPI derivatives, its importance during a photobiological process has been evidenced. kINP is the key compound involved in thymine dimers formation during the photosensitization of DNA by indoprofen, a nonsteroidal antiinflammatory drug.