Orientation Dependence in Triplet–Triplet Energy Transfer: Analysis of Magnetophotoselection Experiments

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Abstract
We have examined theoretically and experimentally triplet–triplet energy transfer for several different donor–acceptor pairs dissolved in low‐temperature glasses in order to determine if there is some observable preferred mutual orientation for energy transfer, especially at large intermolecular distances. In particular, we have analyzed experiments that used magnetophotoselection techniques. Our results substantially support earlier findings that indicated the absence of observable orientation effects. In analyzing our experiments, we find that for any given system a large fraction of the donor molecules will transfer efficiently and will exhibit little in the way of orientation effects unless delta‐function‐type orientation dependences exist. Even at low acceptor concentrations, these molecules represent a significant portion of all molecules that transfer and their presence will tend to minimize experimentally observable effects.