A directly fused tetrameric porphyrin sheet and its anomalous electronic properties that arise from the planar cyclooctatetraene core

Yasuyuki Nakamura, Naoki Aratani, Hiroshi Shinokubo, Akihiko Takagi, Tomoji Kawai, Takuya Matsumoto, Zin Seok Yoon, Deok Yun Kim, Tae Kyu Ahn, Dongho Kim, Atsuya Muranaka, Nagao Kobayashi, Atsuhiro Osuka

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Abstract

Oxidation of a directly meso-meso linked cyclic porphyrin tetramer 2 gave a porphyrin sheet 3. The symmetric square structure of 3 is indicated by its simple 1H NMR spectrum that exhibits only two signals for the porphyrin β-protons. The absorption spectrum of 3 displays characteristic Soret-like broad bands and weak Q-bands, and its magnetic circular dichroism (MCD) spectrum exhibits a negative Faraday A term at the 762 nm band as a rare case, indicating the absorption as a transition from a nondegenerate level to a degenerate level. A slightly longer S1-state (1.1 ps) and smaller TPA cross section (2750 GM) than a tetrameric linear porphyrin tape also indicate its unique electronic properties. The porphyrin sheet 3 forms stable 1:2 complexes with guest molecules G1 and G2, whose 1H NMR spectra exhibit remarkable downfield shifts for the guest protons that are located just above the cyclooctatetraene (COT) core of 3, whereas the imidazolyl protons bound to the zinc(II) porphyrin local cores are observed at slightly upfield positions. These results have been qualitatively accounted for in terms of the presence of a strong paratropic ring current around the COT core that propagates through the whole π-electronic network of 3, hence competing with and canceling the weak diatropic ring currents of the local zinc(II) porphyrins. This explanation was supported by DFT calculation performed at the GIAO-B3LYP/6-31G* level, which indicated large positive NICS values within the COT core and small NICS values within the local zinc(II) porphyrins.

Original languageEnglish
Pages (from-to)4119-4127
Number of pages9
JournalJournal of the American Chemical Society
Volume128
Issue number12
DOIs
Publication statusPublished - 2006 Mar 29

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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    Nakamura, Y., Aratani, N., Shinokubo, H., Takagi, A., Kawai, T., Matsumoto, T., Yoon, Z. S., Kim, D. Y., Ahn, T. K., Kim, D., Muranaka, A., Kobayashi, N., & Osuka, A. (2006). A directly fused tetrameric porphyrin sheet and its anomalous electronic properties that arise from the planar cyclooctatetraene core. Journal of the American Chemical Society, 128(12), 4119-4127. https://doi.org/10.1021/ja057812l