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

摘要

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-l,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 Mobius 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.