Spin polarization of charge-transfer triplet excitons in phenanthrene–PMDA single crystals

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Abstract
The spin polarization of charge-transfer triplet excitons in phenanthrene–PMDA single crystals is investigated in detail. It is shown that the symmetry of the tensor which describes the population inversion of the spin levels is due to small nπ* and ππ* admixtures, localized on the PMDA molecule. These admixtures to the total charge–transfer triplet wavefunction are so small that they can be neglected for the calculation of the triplet energy levels (zero field splitting tensor), yet they dominate the intersystem crossing process and determine the symmetry of the observed spin polarization.