Synthesis and Photophysical Properties of Porphyrin Macrorings Composed of Free-Base Porphyrins and Slipped-Cofacial Zinc Porphyrin Dimers.

The self-assembled macroring N-(Zn-Fb-Zn)3 has been constructed by intermolecular complementary coordination among three trisporphyrin Zn-Fb-Zn molecules, each of which consists of a central free-base porphyrin and two imidazolyl-zinc-porphyrin ends. Thus, N-(Zn-Fb-Zn)3 has three slipped-cofacial zinc porphyrin dimers ("special pair model") and three free-base porphyrins, alternately. The zinc porphyrin dimers in N-(Zn-Fb-Zn)3 are covalently connected by a ring-closing olefin metathesis reaction between the allyl ether groups substituted on the zinc porphyrin dimers, giving a covalently linked macroring C-(Zn-Fb-Zn)3. The fluorescence spectra of C-(Zn-Fb-Zn)3 in several solvents show that the photoinduced energy transfer from one of the zinc porphyrin dimers to a free-base porphyrin occurs intramolecularly in toluene, whereas the photoinduced electron transfer predominantly occurs intramolecularly in N,N-dimethylformamide. Treatment of C-(Zn-Fb-Zn)3 with copper(II) acetate gives a Cu-containing heteromultinuclear porphyrin macroring C-(Zn-Cu-Zn)3, demonstrating that C-(Zn-Fb-Zn)3 could be a good precursor to construct various heteromultinuclear porphyrin macrorings.