Synthesis and Atropisomerism of Cascaded Tetraphenylporphyrin-[60]Fullerene Hybrids

Article abstract of DOI:10.1002/chem.201501254

Flexible, linked dendritic tetraphenylporphyrin (TPP)-fullerene hybrids were synthesized. They were designed to gain insight into and mimic the primary events in the natural photosynthetic reaction center. These multiporphyrin moieties are based on a light-harvesting concept. Moreover, they incorporate multiple redox components aligned along a redox gradient. Newkome-type dendrons were added to these TPP-fullerene hybrids. In principle they can mediate pH-dependent water solubility, which, however, could not be observed in this case. A protecting-group strategy using tert-butyldiphenylsilyl groups allows convergent synthesis of the dendritic compounds. The dendritic multiporphyrins were synthesized separately and can be used as individual building blocks. Atropisomerism was observed in the dendritic compounds, and single atropisomers could be assigned to the corresponding peaks of a characteristic pattern in the NMR spectra. Deprotection of the Newkome-type dendrons was shown to be feasible under mild conditions that leave the redox gradient intact. Redox gradient: Flexible dendritic porphyrin-fullerene hybrids were synthesized. They comprise a large dendritic redox gradient Fc₉-(ZnP)₃-H₂P-C₆₀ (Fc: ferrocene, ZnP: zinc porphyrin, H₂P: free-base porphyrin, and C₆₀: fullerene), in which multiple porphyrins are embedded for light harvesting (see figure). Porphyrin-fullerene compounds with attached Newkome-type dendrons were also synthesized. They could be deprotected in a mild manner to give dendritic products with free carboxyl groups.