Kinetics of populating and decay of the phosphorescent state of tetramethylpyrazine in durene. A system with skew spin axes

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Abstract
Using microwave induced phosphorescence techniques we determined the rate constants for populating and decay of the lowest triplet state of tetramethylpyrazine (TMP) in a durene crystal. The dynamic behaviour of the spin states Ty′ and Tz′ corresponding to the in-plane spin axes (principal axes of the dipolar coupling tensor) y′ and z′ proves to be identical : ky′ r = kz′ r (radiative decay), ky′ = kz′ (absolute decay rates) and Py′ = Pz′ (populating rates). This result supports the suggestion of de Groot et al., based on E.S.R. experiments, that for the phosphorescent state of TMP in the durene host the in-plane spin axes y′ and z′ have undergone an appreciable (≈45°) rotation with respect to the in-plane molecular axes y and z.