Viscosity Dependence of the First-Order Decay of the Triplet State of Anthracene and Related Molecules

Abstract

In fluid (nonviscous) solvents, the first‐order term in the rate equation for the decay of the triplet state of an aryl hydrocarbon appears to be the sum of a unimolecular, practically temperature‐independent process and a bimolecular quenching reaction involving an adventitious quencher, present in trace amounts. The rate of this bimolecular reaction is diffusionally limited, over a wide range of temperatures and viscosities. In highly viscous media, the temperature dependent components of the first‐order reactions have energies of activation ranging from 0.8 to 0.3 of the value which corresponds to the variation of the viscosity of the solvent with temperature.