Applicability of the kinematic pair-density-matrix theory to optically detected magnetic-resonance spectra of two-dimensional molecular crystals

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Abstract
The kinematic pair-density-matrix theory of triplet-pair annihilation has been applied including the dimensionality of exciton motion to optically detected magnetic-resonance (ODMR) spectra observed optically in two-dimensional molecular crystals under microwave perturbation of a static magnetic field. It is shown that, contrary to previous work with the kinetic scheme, the kinematic approach using the known parameters of motion provides an excellent fit of ODMR spectra for both fusion of triplet pairs in anthracene and for fission of singlets into pairs in tetracene. The nearest-neighbor annihilation and the effective exciton decay rates are found to be similar to those used in the literature to account for the shapes of the orientational static-field effect. The linewidths of the ODMR resonances are found to be nearest-neighbor-annihilation-rate independent and nearly linearly proportional to the single-exciton effective decay rate in the plane of motion.