Aggregation effects on the optical properties of a light harvesting phenylacetylene dendrimer in non-polar solution

The aggregation of a 4th generation phenylacetlyene dendrimer with a perylene trap at the core (G4PER) is studied in a non-polar solvent environment using steady state absorption, fluorescence and fluorescence excitation spectroscopy, and time-dependent fluorescence measurements as a function of G4PER concentration. At relatively low G4PER concentrations (<10−7 M) in isopentane, the spectral data suggest that G4PER dendrimers are mainly in monomeric form. As the concentration increases above 10−7 M in isopentane the spectral properties conclusively show the formation of dendritic aggregates, indicated by changes in the spectral region of the perylene trap. The time-dependent fluorescence data support the steady state measurements, indicating the presence of multiple emitters at high sample concentrations with fluorescence decay curves defined by multi-exponential functions. In contrast, in dichloromethane, a solvent of higher dielectric constant, the steady state and time resolved spectroscopic data at similar G4PER concentrations display no spectral or temporal signatures due to dendritic aggregation. This paper also addresses the nature of the new aggregate electronic transitions formed in the spectral region of the perylene trap.