Intramolecular energy hopping in polyphenylene dendrimers with an increasing number of peryleneimide chromophores

The photophysical properties and the excitation energy transfer (EET) proce ss of a series of first generation dendrimers having a rigid tetrahedral co re and different numbers of peryleneimide chromophores at the rim were inve stigated by steady-state and time-resolved fluorescence spectroscopy in tol uene. It was shown that the model dendrimer containing only one chromophore decays monoexponentially with a time constant of 4.2 ns. In the multichrom ophoric compounds an additional long decay time of 7.4 ns assigned to an "e xcimer-like" state was observed, and its contribution increases with the nu mber of chromophores. The time-resolved polarization measurements resulted in a nanosecond relaxation component due to the rotation of the entire dend ritic structure. However, for the compounds having more than one chromophor e, an additional fast anisotropy decay time of 100-200 ps was observed whic h corresponds to Forster type EET among the chromophores.