A New Strategy for Construction of Covalently Linked Giant Porphyrin Arrays with One, Two, and Three Dimensionally Arranged Architectures

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Abstract
Synthesis, structural characteristics, and optical and electrochemical properties of various meso–meso-linked porphyrin arrays were described. The AgI-salt-promoted meso–meso coupling reaction of 5,15-diaryl and 5,10,15-triaryl ZnII-porphyrins is advantageous in light of its high regioselectivity as well as its easy extension to large porphyrin arrays. A similar coupling reaction is also possible by electrochemical oxidations for ZnII- and MgII-porphyrins, while the electrochemical oxidation of NiII-, PdII, and CuII-porphyrins led to formation of meso-β linked biporphyrins with high regio-selectivity. As an extension of the above AgI-promoted coupling reaction, 1,4-phenylene-bridged linear porphyrin arrays were coupled to give orthogonally arranged windmill-like porphyrin arrays, which in turn were further coupled to afford grid-like porphyrin arrays of giant size. In all the ZnII-metallated windmill arrays, the intramolecular singlet–singlet excitation energy transfer proceeds efficiently from the peripheral porphyrins to the central biporphyrin core. The doubling reaction was repeated up to the synthesis of 128-mer. During these attempts, many meso–meso-linked porphyrin arrays were isolated in a discrete form by repetitive gel-permeation chromatography (GPC)–HPLC, all exhibiting high solubility in common organic solvents in spite of their giant molecular sizes. Finally, the oxidation with strong oxidant tris(4-bromophenyl)aminium hexachloroantimonate allowed the coupling of 5,10,15-triaryl NiII- and PdII-porphyrins to meso-β doubly-linked fused biporphyrins and the smooth conversion of meso–meso-linked CuII-biporphyrin to meso–meso β–β β–β triply-linked biporphyrin. These fused biporphyrins exhibit full π-conjugation over the arrays.

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