Directly meso-meso linked porphyrin rings: Synthesis, characterization, and efficient excitation energy hopping

Yasuyuki Nakamura, In Wook Hwang, Naoki Aratani, Tae Kyu Ahn, Dah Mee Ko, Akihiko Takagi, Tomoji Kawai, Takuya Matsumoto, Dongho Kim, Atsuhiro Osuka

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Abstract

Directly meso-meso linked porphyrin rings CZ4, CZ6, and CZ8 that respectively comprise four, six, and eight porphyrins have been synthesized in a stepwise manner from a 5, 10-diaryl zinc(II) porphyrin building block. Symmetric cyclic structures have been indicated by their very simple 1H NMR spectra that exhibit only a single set of porphyrin and their absorption spectra that display a characteristic broad nonsplit Soret band around 460 nm. Energy minimized structures calculated at the B3LYP/6-31G* level indicate that a dihedral angle between neighboring porphyrins decreases in order of CZ6 > CZ8 > CZ4, which is consistent with the 1H NMR data. Photophysical properties of these molecules have been examined by the steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related with the excitation energy migration processes within the porphyrin rings, where the exciton-exciton annihilation time and the polarization anisotropy rise time are well described in terms of the Förster-type incoherent energy hopping model. Consequently, the excitation energy hopping rates have been estimated for CZ4 (119 ± 2 fs)-1, CZ6 (342 ± 59 fs)-1, and CZ8 (236 ± 31 fs)-1, which reflect the magnitude of the electronic coupling between the neighboring porphyrins. Overall, these porphyrin rings serve as a well-defined wheel-shaped light harvesting antenna model in light of very efficient excitation energy hopping along the ring.

Original languageEnglish
Pages (from-to)236-246
Number of pages11
JournalJournal of the American Chemical Society
Volume127
Issue number1
DOIs
Publication statusPublished - 2005 Jan 12

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All Science Journal Classification (ASJC) codes

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

Cite this

Nakamura, Y., Hwang, I. W., Aratani, N., Ahn, T. K., Ko, D. M., Takagi, A., Kawai, T., Matsumoto, T., Kim, D., & Osuka, A. (2005). Directly meso-meso linked porphyrin rings: Synthesis, characterization, and efficient excitation energy hopping. Journal of the American Chemical Society, 127(1), 236-246. https://doi.org/10.1021/ja045254p