Globular dendrimers involving a C60 core and a tetraphenyl porphyrin function

A series of highly compact globular dendrimers, 5, 21, and 22, involving a C-60 core with a T-h symmetrical addition pattern was synthesized by way of the fivefold cyclopropanation of the fullerene-porphyrin dyad 2 with dendritic malonates in the remaining octahedral positions. Whereas 5 contains classical Frechet benzyl-ether-based systems, a new type of dendra containing a flexible spacer between the branching units was developed for the synthesis of 21 and 22. The spectroscopic, electrochemical, and photophysical properties of the tetraphenylporphyrin-zinc (Zn-TPP) chromophore within the functional dendrimers depend not only on the presence but also on the generation number of the surrounding dendra and therefore on the nanoenvironment provided by the neighboring addends. This is reflected, for example, in the bathochromic shifts of the Soret and Q-bands of the porphyrin moiety and in the shift of the first reduction potentials to more negative values for both the fullerene and porphyrin moieties with increasing generation number. Whereas in the dyad 2 a photsinduced electron transfer from the porphyrin to the fullerene can occur, dendrimers 21 and 22 show fluorescence properties and singlet oxygen formation properties (Phi(Delta) = 0.66-0.67) reminiscent to those of the parent Zn-TPP.