Time Resolved EPR of Triplet Excitons in Phenazine-TCNQ Charge Transfer Crystal

Transient nutation EPR spectroscopy has been applied to study the dynamical properties of the excited triplets in the Phenazine-Tetracyanoquinodimethane 1 : 1 CT crystal. Measurements have been carried out with the magnetic field set along the principal axes of the ZFS tensor. Spin-spin and spin-lattice relaxation times have been determined at different temperatures together with the decay rate constants from the triplet sublevels which are found to be highly spin selective. The temperature dependence of the initial optical electron polarization carried by the triplet has been also analyzed. It is shown that the singlet fission and the intersystem crossing caused by spin-orbit coupling are both responsible for the generation of the triplet in this crystal, the former prevailing at room temperature. Our results are in agreement with previous investigations on the same crystal.