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Belt-Shaped pi-Systems: Relating Geometry to Electronic Structure in a Six-Porphyrin Nanoring

Sprafke, Johannes K.; Kondratuk, Dmitry V.; Wykes, Michael; Thompson, Amber L.; Hoffmann, Markus; Drevinskas, Rokas LU ; Chen, Wei-Hsin; Yong, Chaw Keong; Karnbratt, Joakim and Bullock, Joseph E., et al. (2011) In Journal of the American Chemical Society 133(43). p.17262-17273
Abstract
Linear pi-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of pi-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a pi-conjugated butadiyne-linked cyclic porphyrin hexamer directly from the monomer. Small-angle X-ray scattering data show that this nanoring is shape-persistent in solution, even without its template, whereas the linear porphyrin hexamer is relatively flexible. The crystal structure of the nanoring-template complex shows that most of the strain is localized in the acetylenes; the porphyrin units are slightly curved, but the zinc... (More)
Linear pi-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of pi-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a pi-conjugated butadiyne-linked cyclic porphyrin hexamer directly from the monomer. Small-angle X-ray scattering data show that this nanoring is shape-persistent in solution, even without its template, whereas the linear porphyrin hexamer is relatively flexible. The crystal structure of the nanoring-template complex shows that most of the strain is localized in the acetylenes; the porphyrin units are slightly curved, but the zinc coordination sphere is undistorted. The electrochemistry, absorption, and fluorescence spectra indicate that the HOMO-LUMO gap of the nanoring is less than that of the linear hexamer and less than that of the corresponding polymer. The nanoring exhibits six one-electron reductions and six one-electron oxidations, most of which are well resolved. Ultrafast fluorescence anisotropy measurements show that absorption of light generates an excited state that is delocalized over the whole pi-system within a time of less than 0.5 ps. The fluorescence spectrum is amazingly structured and red-shifted. A similar, but less dramatic, red-shift has been reported in the fluorescence spectra of cycloparaphenylenes and was attributed to a high exciton binding energy; however the exciton binding energy of the porphyrin nanoring is similar to those of linear oligomers. Quantum-chemical excited state calculations show that the fluorescence spectrum of the nanoring can be fully explained in terms of vibronic Herzberg-Teller (HT) intensity borrowing. (Less)
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Journal of the American Chemical Society
volume
133
issue
43
pages
17262 - 17273
publisher
The American Chemical Society
external identifiers
  • wos:000297380900031
  • scopus:80055019999
ISSN
1520-5126
DOI
10.1021/ja2045919
language
English
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1ef51539-9be0-49ff-8807-07351e155a74 (old id 2291740)
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2012-01-11 12:37:41
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@article{1ef51539-9be0-49ff-8807-07351e155a74,
  abstract     = {Linear pi-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of pi-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a pi-conjugated butadiyne-linked cyclic porphyrin hexamer directly from the monomer. Small-angle X-ray scattering data show that this nanoring is shape-persistent in solution, even without its template, whereas the linear porphyrin hexamer is relatively flexible. The crystal structure of the nanoring-template complex shows that most of the strain is localized in the acetylenes; the porphyrin units are slightly curved, but the zinc coordination sphere is undistorted. The electrochemistry, absorption, and fluorescence spectra indicate that the HOMO-LUMO gap of the nanoring is less than that of the linear hexamer and less than that of the corresponding polymer. The nanoring exhibits six one-electron reductions and six one-electron oxidations, most of which are well resolved. Ultrafast fluorescence anisotropy measurements show that absorption of light generates an excited state that is delocalized over the whole pi-system within a time of less than 0.5 ps. The fluorescence spectrum is amazingly structured and red-shifted. A similar, but less dramatic, red-shift has been reported in the fluorescence spectra of cycloparaphenylenes and was attributed to a high exciton binding energy; however the exciton binding energy of the porphyrin nanoring is similar to those of linear oligomers. Quantum-chemical excited state calculations show that the fluorescence spectrum of the nanoring can be fully explained in terms of vibronic Herzberg-Teller (HT) intensity borrowing.},
  author       = {Sprafke, Johannes K. and Kondratuk, Dmitry V. and Wykes, Michael and Thompson, Amber L. and Hoffmann, Markus and Drevinskas, Rokas and Chen, Wei-Hsin and Yong, Chaw Keong and Karnbratt, Joakim and Bullock, Joseph E. and Malfois, Marc and Wasielewski, Michael R. and Albinsson, Bo and Herz, Laura M. and Zigmantas, Donatas and Beljonne, David and Anderson, Harry L.},
  issn         = {1520-5126},
  language     = {eng},
  number       = {43},
  pages        = {17262--17273},
  publisher    = {The American Chemical Society},
  series       = {Journal of the American Chemical Society},
  title        = {Belt-Shaped pi-Systems: Relating Geometry to Electronic Structure in a Six-Porphyrin Nanoring},
  url          = {http://dx.doi.org/10.1021/ja2045919},
  volume       = {133},
  year         = {2011},
}