Discrete Giant Porphyrin Arrays: Challenges to Molecular Size, Length and the Extent of Electronic π-Conjugation

Our studies on synthesis of directly meso-meso-linked and fused porphyrin arrays were reviewed. Ag^I-promoted meso-meso coupling reaction of 5,15-diaryl Zn^II-porphyrins is advantageous in light of its high regioselectivity as well as its easy extension to large porphyrin arrays. Doubling reactions have been repeated to make 128-mer as the longest man-made discrete molecule. The similar coupling reaction has been applied to 1,4-phenylene-bridged linear porphyrin arrays, providing three dimensionally arranged windmill porphyrin arrays and grid-like porphyrin arrays. meso-β Doubly-linked diporphyrins were prepared by oxidations of 5,15-diaryl Cu^II-, Ni^II-, and Pd^II-porphyrins with (p-BrC₆H₄)₃NSbCl₆ (BAHA). In a similar manner, meso,meso-end capped meso-meso linked Cu^II-, Ni^II-, and Pd^II-diporphyrins were converted into meso-meso β-β, β-β triply-linked fused diporphyrins. We developed an alternative, more effective method to convert meso-meso-linked diporphyrins to triply-linked diporphyrins by using DDQ as an oxidant in the presence of Sc^III-salt, which, when applied to higher meso-end capped meso-meso linked Zn^II-porphyrin arrays, allowed the synthesis of fully conjugated triply-linked Zn^II-porphyrin arrays up to 12-mer which exhibited a low-energy electron absorption band reaching the infrared region.

porphyrins - oxidation - oligomers - π-conjugation - molecular wires