Assignment of transient species observed on laser flash photolysis of p-benzoquinone and methylated p-benzoquinones in aqueous solution

Abstract

Short-lived transient spectra observed on nanosecond laser flash photolysis of p-benzoquinone, toluquinone, p-xyloquinone and cumoquinone in aqueous solutions have first-order decay rate constants of 1.9 × 10⁶, 2.7 × 10⁶, 1.2 × 10^–6 and 1.7 × 10⁵ s^–1, respectively. The spectra are assigned to the lowest triplet absorption T_nâ†� T₁. These short-lived species give rise to long-lived transients due to the semiquinone radicals QH· and Q·^–, as well as a species considered to be the quinonehydroxy radical adduct (QOH·).