Spectral and redox properties of zinc porphyrin core dendrimers with triarylamines as dendron.

The first and second generation of zinc porphyrin core dendrimers (3 and 4) with triarylamine as dendron have been synthesized via Ullmann coupling reaction. Their absorption and emission spectra indicate that there are strong interactions between zinc porphyrin core and triarylamine dendrons. Zinc porphyrin links with triarylamine causes Soret band broadening and Q band shift as compared with ZnTPP. Because of the antenna effect on these dendrimers, the fluorescence quantum yields were strongly enhanced when more triarylamine moieties were linked. Cyclic voltammetry and spectroelectrochemical methods were used to investigate the redox properties of dendrimers. Axial ligation of zinc porphyrin with N-methylimidazole is useful in differentiating the oxidation site of dendrimers. For the first generation dendrimer (3), porphyrin ring oxidation potential shifts cathodically because the periphery dendrons are strong electron-donating groups. On the other hand, the dendrons of the second generation (4) are oxidized first and generate an atmosphere of eight positive charges. The porphyrin ring core is then oxidized with an anodic shift in potential due to the electron-withdrawing effect of the oxidized substituents.