Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring.
Linear π-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of π-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed syn...
| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
2011
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| _version_ | 1826257560064229376 |
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| author | Sprafke, J Kondratuk, D Wykes, M Thompson, A Hoffmann, M Drevinskas, R Chen, W Yong, C Kärnbratt, J Bullock, J Malfois, M Wasielewski, MR Albinsson, B Herz, L Zigmantas, D Beljonne, D Anderson, H |
| author_facet | Sprafke, J Kondratuk, D Wykes, M Thompson, A Hoffmann, M Drevinskas, R Chen, W Yong, C Kärnbratt, J Bullock, J Malfois, M Wasielewski, MR Albinsson, B Herz, L Zigmantas, D Beljonne, D Anderson, H |
| author_sort | Sprafke, J |
| collection | OXFORD |
| description | Linear π-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of π-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a π-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 π-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. |
| first_indexed | 2024-03-06T18:20:09Z |
| format | Journal article |
| id | oxford-uuid:05ffa071-02d8-4134-aa23-44036f442fa1 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T18:20:09Z |
| publishDate | 2011 |
| record_format | dspace |
| spelling | oxford-uuid:05ffa071-02d8-4134-aa23-44036f442fa12022-03-26T09:00:23ZBelt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring.Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:05ffa071-02d8-4134-aa23-44036f442fa1EnglishSymplectic Elements at Oxford2011Sprafke, JKondratuk, DWykes, MThompson, AHoffmann, MDrevinskas, RChen, WYong, CKärnbratt, JBullock, JMalfois, MWasielewski, MRAlbinsson, BHerz, LZigmantas, DBeljonne, DAnderson, HLinear π-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of π-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a π-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 π-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. |
| spellingShingle | Sprafke, J Kondratuk, D Wykes, M Thompson, A Hoffmann, M Drevinskas, R Chen, W Yong, C Kärnbratt, J Bullock, J Malfois, M Wasielewski, MR Albinsson, B Herz, L Zigmantas, D Beljonne, D Anderson, H Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring. |
| title | Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring. |
| title_full | Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring. |
| title_fullStr | Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring. |
| title_full_unstemmed | Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring. |
| title_short | Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring. |
| title_sort | belt shaped π systems relating geometry to electronic structure in a six porphyrin nanoring |
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