Poly(amidoamine) dendrimers with phenyl shells: fluorescence and aggregation behavior

The fluorescence and aggregation behavior of poly(amidoamine) (PAMAM) dendrimers modified with phenyl groups at the periphery (PAMAM-P) were investigated. For comparison, the third generation (G3) PAMAM dendrimer with a shell of positive charge (PAMAM-PA) was also synthesized. PAMAM-P G3, G4 and G5 show dual fluorescence emission due to the fluorescence emission of phenyl ring and its excimer. By increasing the generation number from G2 to G4, the fluorescence intensity of phenyl ring decreases, and the fluorescence of phenyl excimer appears and becomes obvious. The three-dimensional geometry arrangement or dendrimer architecture was found to have a strong effect on their fluorescence behavior. This result is further supported by the solvent effect and model compound studies. The lower generations (PAMAM-P G0 to G3) were self-organized into spherical aggregates. However, no aggregation behavior was observed for the higher generations (>G3). The critical aggregation concentration (CAC) values measured by fluorescence spectroscopy were found to decrease gradually with increasing generation number from G0 to G3.