Energy Migration in Organic Liquids at High Temperatures

The energy‐transfer process in organic liquids has been studied at temperatures from 20°–240°C. The results are consistent with the migration model, according to which electronic excitation energy undergoes a series of hops between neighboring solvent molecules, followed by a short‐range jump to a solute molecule. The mean hopping time ${\tau }_h$ is related by theory to an experimentally determinable parameter $\alpha$ , which is directly related to the hopping frequency. Values of $\alpha$ , all on the order of 10¹² sec⁻¹, were found for a number of solutions. For a temperature increase of 200°C, $\alpha$ was generally found to decrease by about 50%, depending on the solvent utilized. Relationships between the temperature dependence of ${\tau }_h$ and that of mean intermolecular distance are discussed. Material diffusion in the energy‐transfer processes is estimated to be quite small compared with hopping, at least for efficient solvents. Anomalies in the energy‐transfer properties of anisole are noted.