meso–meso Linked Porphyrin–[26]Hexaphyrin–Porphyrin Hybrid Arrays and Their Triply Linked Tapes Exhibiting Strong Absorption Bands in the NIR Region

We describe the synthesis and characterization of directly meso–meso linked porphyrin–[26]­hexaphyrin–porphyrin hybrid oligomers and their triply linked (completely fused) hybrid tapes. meso–meso Linked Ni­(II) porphyrin–[26]­hexaphyrin–Ni­(II) porphyrin trimers were prepared by methanesulfonic acid-catalyzed cross-condensation of meso-formyl Ni­(II) porphyrins with a 5,10-diaryltripyrrane followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The Ni­(II) porphyrin moieties were converted to Zn­(II) porphyrins via an indirect route involving reduction of the [26]­hexaphyrin to its 28π congener, acid-induced denickelation, oxidation of the [28]­hexaphyrin, and finally Zn­(II) ion insertion. Over the course of these transformations, porphyrin–[28]­hexaphyrin–porphyrin trimers have been revealed to take on a Möbius aromatic twisted structure for the [28]­hexaphyrin segment. Oxidation of meso–meso linked hybrid trimer bearing 5,15-diaryl Zn­(II) porphyrins with DDQ/Sc­(OTf)3 under mild conditions resulted in meso–meso coupling oligomerization, affording the corresponding dimeric (hexamer), trimeric (nonamer), and tetrameric (dodecamer) oligomers. On the other hand, oxidation of a meso–meso linked hybrid trimer bearing 5,10,15-triaryl Zn­(II) porphyrin terminals with DDQ/Sc­(OTf)3 under harsher conditions afforded a meso–meso, β–β, β–β triply linked hybrid porphyrin tape, which displays a sharp and intense absorption band at 1912 nm. Comparison of this extremely red-shifted absorption band with those of Zn­(II) porphyrin tapes suggests that the bathochromic-shifting capability of a [26]­hexaphyrin unit is large, almost equivalent to that of four individual Zn­(II) porphyrin units. As demonstrated, the fusion of porphyrins to [26]­hexaphyrin offers an efficient means to expand their conjugation networks, significantly expanding the capabilities attainable for these chromophores.