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

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 T_y′ and T_z′ corresponding to the in-plane spin axes (principal axes of the dipolar coupling tensor) y′ and z′ proves to be identical : k_y′ ^r = k_z′ ^r (radiative decay), k_y′ = k_z′ (absolute decay rates) and P_y′ = P_z′ (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.