Long range mechanism for the temperature dependence of the ratio of delayed monomer and delayed excimer fluorescence following triplet–triplet annihilation in liquids

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.