Singlet→triplet absorption spectra of substituted benzenes

Abstract

S₀→T₁ absorption spectra of 11 fluorobenzenes, the xylenes and m- and p-hexafluoroxylenes, the fluorotoluenes and trifluoromethylbenzenes, toluene and benzene have been measured using the technique of O₂ perturbation. Comparison is made between the triplet energies obtained from these spectra and those obtained using other techniques and calculations. The oxygen perturbed S₀→T₁ absorption method was found to be a simple and useful method of obtaining triplet energies for molecules in which the S₁ and T₁ levels had a large energy separation. Vibrational assignments of triplet state frequencies were not possible for most of the compounds as the spectra were essentially featureless. It was found that the S₁– T₁ energy gap varied little from compound to compound. The triplet energy levels are discussed in relation to measured triplet state quenching parameters.