Laser photolysis studies of the triplet state of xanthone and its ketyl radical in fluid solution

Abstract

A strong transient absorption with a peak near 600 nm has been observed following laser photolysis of xanthone in fluid solution: this absorption is due to the first excited triplet state of xanthone and an estimate of its extinction coefficient is given. Triplet decay in various solvents depends upon solvent dielectric and hydrogen atom donating ability; however, an unusually short lifetime of 92 ns is noted with benzene as solvent. The quenching constants of triplet xanthone by naphthalene, oxygen and 3-methylindole are 9.5, 5.6 and 8.4 × 10⁹ dm³ mol^–1 s^–1 respectively. Oxygen quenching is greater than the expected limiting value of one ninth diffusion controlled.

In the presence of hydrogen donors the xanthone triplet state is shown to react to give xanthone ketyl radical the absorption spectrum of which has been measured in several solvents. The decay of this radical in the presence and absence of oxygen has also been investigated.