Construction of dendrimers with a square-shaped core consisting of zinc chlorophyll assembly via intermolecular nitrogen–zinc coordination

The first dendrimers consisting of self-assembled zinc chlorophyll derivatives are reported. Coordination-directed self-assembly of pyridine-appended zinc chlorophyll derivatives tethering a dendron moiety results in cyclic tetramers peripherally functionalized by dendrons via intermolecular axial coordination interaction between the nitrogen atom in the pyridine ring and the zinc atom in the chlorin ring. We characterized the formation of the cyclic tetramers by use of 1 H NMR measurements including diffusion-ordered spectroscopy (DOSY). Four different types of dendrons were introduced in the zinc chlorophyll component to investigate the tolerance of the self-assembly to the dendron structure. All dendrimers exhibited similar stabilities, which demonstrates that the dendron moiety does not interfere with the self-assembly, such that more than 90% of the molecules are in the assembly at concentrations >0.2 mM in benzene.