The synthesis and characterization of dendron-coated porphyrins up to the fifth generation are described. Both free base and zinc-cored tetraphenylporphyrin (TPPH 2 and TPPZn) were used, from which the dendrons were divergently grown using the anhydride of acetonide-protected bis-MPA (acetonide-2,2-bis(methoxy)propanoic anhydride). It is shown that a spacer must be attached to the porphyrin to increase the hydrolytic stability and allow synthesis of higher generations. Direct coupling of dendrons to the porphyrins was also investigated but failed to give full substitution of the porphyrin core. The absorption and fluorescence emission data for the TPPZn dendrimers indicate that the porphyrin configuration may change at higher generations. The hydrodynamic volume of the dendrimers is calculated from the polarization anisotropy decay data. It is shown that these bis-MPA dendrimers are significantly smaller than the same generation Fréchet-type benzyl ether TPP dendrimer.
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Vestberg et al. (2004) studied this question.