Abstract
The temperature dependence of the ratio, α, of the rates of formation of excimer (1D*) and excited monomer (1M*) following triplet–triplet annihilation of aromatic molecules, is examined using two models. The first assumes that the annihilation occurs solely in a solvent cage and leads to 1D* and (1M* and 1M) formation; it includes separation and re-encounter of 1M* and 1M. This model produces only a weak dependence of α on temperature. The second model permits, in addition, long range annihilation to form 1M* and 1M with a rate constant which falls off exponentially with separation. It uses the diffusion model developed recently by Pilling and Rice and incorporates an analysis of encounter/re-encounter processes for 1M* and 1M formed by both the long range and cage processes. This model is able to reproduce the experimental temperature dependence with realistic parameters for the long range interaction.

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