A new strategy for construction of covalently linked giant porphyrin arrays with one, two, and three dimensionally arranged architectures

Synthesis, structural characteristics, and optical and electrochemical properties of various meso-meso-linked porphyrin arrays were described. The Ag-I-salt-promoted meso-meso coupling reaction of 5,15-diaryl and 5,10,15-triaryl Zn-II-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 Zn-II- and Mg-II-porphyrins, while the electrochemical oxidation of Ni-II-, Pd-II, and Cu-II-porphyrins led to formation of meso-beta linked biporphyrins with high regioselectivity. As an extension of the above Ag-I-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 Zn-II-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 Ni-II- and Pd-II-porphyrins to meso-beta doubly-linked fused biporphyrins and the smooth conversion of meso-meso-linked Cu-II-biporphyrin to meso-meso beta-beta beta-beta triply-linked biporphyrin. These fused biporphyrins exhibit full pi -conjugation over the arrays.