Generation-Dependent Energy Dissipation in Rigid Dendrimers Studied by Femtosecond to Nanosecond Time-Resolved Fluorescence Spectroscopy

Abstract

Intramolecular kinetic processes in a series of second-generation polyphenyl dendrimers with multiple peryleneimide chromophores attached to the para position of the outer phenyl ring were investigated by steady-state and femtosecond to nanosecond time-resolved fluorescence spectroscopy. The results obtained were compared to the ones of the corresponding first-generation dendrimer series. The energy-hopping rate constant, khopp, observed from anisotropy decay times was found to be 5 times smaller than that of the first-generation series and scales well with the difference in average distance between the chromophores. In addition to the processes observed in first-generation dendrimers in the ultrafast time domain by fluorescence up-conversion, a second annihilation process is found in the second-generation multichromophoric dendrimer. The observation of two singlet−singlet annihilation processes in this compound can be explained by the presence of a mixture of constitutional isomers leading to a broader distribution of distances between neighboring chromophores compared to first-generation multichromophoric dendrimers.