Ligand-Binding Ability of a Porphyrin Core in a Dendrimer with Rigid Branched Terminal Components.

A dendrimer with rigid branched terminal components was prepared by a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction. A zinc 5,15-diethynyl-10,20-bis(3,5-di- tert-butylphenyl)porphyrin unit was incorporated at the core of the dendrimer as a receptor site for an added pyridyl ligand. The appearance of an absorption band characteristic of the planar conformer of conjugated chains in the terminal components suggested that the dendrimer adopts a folded higher order structure in dichloromethane at 25 °C. The binding constant between the zinc porphyrin core and a pyridyl ligand was evaluated by means of UV-vis absorption titration and compared with that of a suitable reference compound. The incorporation of the zinc porphyrin core into the folded dendrimer led to considerable suppression of its ligand-binding ability.