Knowledge Bank

The kinetics for formation and dissociation of intramolecular excimers in 1,3-bis(N-carbazolyl)propane have been studied in a large number of solvents using time-resolved fluorescence techniques. The rate constants for both formation and dissociation of the intramolecular excimer are seen to decrease with increasing solvent viscosity ($\eta$) as expected for a process requiring an intramolecular rearrangement. No strict functional dependence on viscosity is observed however unless the studies are confined to homologous series of solvents. In a series of alkanes both rate constants are proportional to $\eta -0.34$ and in alcohols to $\eta -0.51$. This anomalous Stokes-Einstein behavior is discussed in terms of the microstructure of the surrounding solvent. Solvent systems of high macroscopic viscosity, formed by the addition of polystyrene, do not effect the kinetics.