We describe the synthesis and characterization of directly meso-meso linked porphyrin-hexaphyrin-porphyrin hybrid oligomers and their triply linked (completely fused) hybrid tapes. meso-meso Linked Ni(II) porphyrin-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 hexaphyrin to its 28π congener, acid-induced denickelation, oxidation of the hexaphyrin, and finally Zn(II) ion insertion. Over the course of these transformations, porphyrin-hexaphyrin-porphyrin trimers have been revealed to take on a Möbius aromatic twisted structure for the 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 hexaphyrin unit is large, almost equivalent to that of four individual Zn(II) porphyrin units. As demonstrated, the fusion of porphyrins to hexaphyrin offers an efficient means to expand their conjugation networks, significantly expanding the capabilities attainable for these chromophores.
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© 2015 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry