Abstract

The formation and quenching of the triplet state of xanthone are studied by femtosecond techniques. As revealed by femtosecond fluorescence spectroscopy, the primarily excited 1ππ* state decays within 1.5 ps. In a transient absorption experiment, this time constant is associated with a partial rise of a triplet signature. This rise has a second and slower component with a time constant of 12 ps. In the presence of high concentrations of the quencher 1-methylnaphthalene, the slow 12 ps rise component is absent. This finding gives strong evidence that the biphasic rise of the triplet absorption of xanthone is due to a sequential mechanism, namely, a 1ππ * → 3nπ* with fast intersystem crossing followed by a 3nπ* → 3ππ* internal conversion. Furthermore, an analysis of the concentration dependence of the quenching kinetics allows one to pin down the intrinsic transfer time of the triplet energy from xanthone to 1-methylnaphthalene to ∼ 1 ps.

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