A Functionalized Noncovalent Macrocyclic Multiporphyrin Assembly from a Dizinc(II) Bis‐Porphyrin Receptor and a Free‐Base Dipyridylporphyrin

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Abstract
The bis‐porphyrin system ZnP2, in which two zinc porphyrins are connected by a phenanthroline linker in an oblique fashion, acts as a bifunctional receptor towards the complexation of free‐base meso‐5,10‐bis(4′‐pyridyl)‐15,20‐diphenylporphyrin (4′‐ cis DPyP). In solution, NMR spectroscopy evidenced quantitative formation of the tris‐porphyrin macrocyclic assembly ZnP2(4′‐ cis DPyP), in which the two fragments are held together by two axial 4′‐N(pyridyl)–Zn interactions. The remarkable stability of the edifice (an association constant of about 6×108 M−1 was determined by UV/Vis absorption and emission titration experiments in toluene) is due to the almost perfect geometrical match between the two interacting units. The macrocycle was crystallized and studied by X‐ray diffraction, which confirmed the excellent complementarity of the two components. Photoinduced energy transfer from the singlet excited state of the zinc porphyrin chromophores to the free‐base porphyrin occurs with an efficiency of 98 % (ken=2×1010 s−1 in toluene, ambient temperature) with a mechanism consistent with a dipole–dipole process with a low orientation factor.

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