Correlated excimer formation and molecular rotational dynamics in phenylacetylene dendrimers

Steady-state and time-resolved fluorescence data are used to examine the photophysical characteristics of a series of phenylacetylene dendrimers. Correlated excimer formation is observed in some solvents which is found to depend strongly upon initial excited-state placement within the dendrimer framework. The results suggest two distinct solvated molecular environments which give rise to independent photophysical behaviors. Models of excimer formation dynamics and relaxation kinetics are described. Additionally, fluorescence anisotropy measurements are examined in the context of simultaneous probe wobbling-in-a-cone and macromolecular dendrimeric rotation as the mechanisms leading to fluorescence depolarization. Approximate solutions to the model are shown to provide good descriptions of the solvated molecular dynamics.