Macromolecular Chemistry and Physics vol:206 issue:1 pages:25-32
The photophysical properties of dendrimers with 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole, also known as DPP, as a core were studied. DPP itself has a high quantum yield of fluorescence, as well as a high molar decadic absorption coefficient, epsilon (epsilon = 33000 L(.)mol(-1.)cm(-1)). The dendrimers, which differ by their substitution pattern, either at the nitrogen (DPPN) or at the carbon (DPPC), are studied in various solvents with different viscosity and solvent-probe interaction and this for several generations and thus varying molecular volume. The stationary measurements show no difference in the absorption and emission spectra for the different generations nor a solvent-effect. Single photon timing is used to determine the fluorescence lifetime, tau. For both dendrimers, the decay curves can be fitted to a monoexponential model. By means of fluorescence depolarization and fluorescence correlation spectroscopy, they hydrodynamic volumes (V-h) are determined. The results for both dendrimers as well as for both techniques are compared. The hydrodynamic radii of DPPN are similar when obtained by FCS compared with anisotropy. When the properties of the different dendrimers are compared, it can be shown that the hydrodynamic volumes of the first generation DPPC dendrimer are much larger compared to V-h of the DPPN dendrimers. The volumes for the third generation are comparable for both substitution patterns.