Synthesis of flexible dendrimers containing porphyrin, anthraquinones and pyromellitimides

The purpose of this work was to synthesize and then characterize the photophysical properties of three series of tetraphenylporphyrin-containing Newkome dendrimers for use in artificial photosynthesis. Two series of these dendrimers were prepared as the free base and zinc metallated porphyrin dendrimers, and had branches emanating from the para positions on the meso phenyl groups of the porphyrin. Steady state and time-resolved fluorescence experiments indicated efficient electron transfer for both series of dendrimers. Intramolecular through-space electron transfer in these dendrimers was attributed to backfolding of the flexible dendritic arms that allowed for close interactions between the anthraquinone groups and the porphyrin core.; The third dendrimer prepared in this work was similar to the first two types of dendrimers described above, but had di-ortho-substitution on the meso phenyl groups of the tetraphenylporphyrin core, and pyromellitimide groups on the terminus. This dendrimer was synthesized in order to explore the effect of added steric congestion around the porphyrin core. The steric congestion was found to inhibit backfolding of the terminal groups and slower electron transfer was observed.