Photophysical processes in the vapour phase measured by the optic–acoustic effect. Part 4.—Radiationless processes from the lowest singlet and triplet states of some simple benzene derivatives

Abstract

The lifetimes in the vapour phase of the vibrationally equilibrated lowest triplet states of toluene and ethylbenzene are reported. Models for the pressure-independent and pressure-dependent parts of the triplet state deactivation are briefly discussed. For [¹H₆]benzene, [²H₆]benzene and toluene the nature of the radiationless processes following intersystem crossing from the first excited singlet state S₁ are analysed. The quantum yields of intersystem crossing from S₁ into the triplet manifold are measured (248 nm excitation) as 0.85 ([¹H₆]benzene), 0.74 ([²H₆]benzene) and 0.77 (toluene) at high pressure.