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Bending a photonic wire into a ring

Abstract

Natural light-harvesting systems absorb sunlight and transfer its energy to the reaction centre, where it is used for photosynthesis. Synthetic chromophore arrays provide useful models for understanding energy migration in these systems. Research has focused on mimicking rings of chlorophyll molecules found in purple bacteria, known as ‘light-harvesting system 2’. Linear mesomeso linked porphyrin chains mediate rapid energy migration, but until now it has not been possible to bend them into rings. Here we show that oligo-pyridyl templates can be used to bend these rod-like photonic wires to create covalent nanorings that consist of 24 porphyrin units and a single butadiyne link. Their elliptical conformations have been probed by scanning tunnelling microscopy. This system exhibits two excited state energy transfer processes: one from a bound template to the peripheral porphyrins and one, in the template-free ring, from the exciton-coupled porphyrin array to the π-conjugated butadiyne-linked porphyrin dimer segment.

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Fig. 1: Porphyrin oligomers.
Fig. 2: Chelation of the binding unit L to l-P2.
Fig. 3: Reaction scheme showing the synthesis of c-P24b via the template complex c-P24b·(T12)2.
Fig. 4: Molecular dynamics simulations of l-P24e·(T12)2.
Fig. 5: STM characterization of c-P24b on Au(111).
Fig. 6: Absorption and fluorescence spectra.

Data availability

All relevant data, including raw computational data, etc., and the x,y,z coordinates of calculated molecular geometries, are available within the paper and its Supplementary Information files, or have been deposited in the Oxford Research Archive34. The NMR and STM data are presented in detail in the main Supplementary Information file and are available upon reasonable request from the authors. Source data are provided with this paper.

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Acknowledgements

We thank the ERC (grant 885606, ARO-MAT) for funding. H.G. thanks the Independent Research Fund Denmark for an International Postdoctoral Fellowship. A.S. thanks the Royal Society for support via a University Research Fellowship. Computational services were provided by the Advanced Research Computing Service at the University of Oxford. M.R. and L.M.H. acknowledge funding by the Engineering and Physical Sciences Research Council UK. L.M.H. acknowledges support through a Hans Fischer Senior Fellowship from the Technical University of Munich’s Institute for Advanced Study, funded by the German Excellence Initiative.

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Authors and Affiliations

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Contributions

H.G., J.-R.D. and J.M.V.R. synthesized and characterized the compounds. J. Hergenhahn and F.D. carried out the computational modelling, after preliminary modelling by H.G., J.-R.D. and J.M.V.R. T.D.W.C. assisted with NMR experiments. A.B.-C., M.C. and A.S. performed the scanning probe microscopy. J. Hart and J.O. prepared samples via electrospray deposition. M.R. and L.M.H. investigated the time-resolved photophysics. H.L.A. and H.G. wrote the paper. All authors discussed the results and edited the manuscript.

Corresponding authors

Correspondence to Alex Saywell, Laura M. Herz or Harry L. Anderson.

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Nature Chemistry thanks Dongho Kim and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–150, Tables 1–13 and notes on photophysics.

Source data

Source Data Fig. 4

Diameter, angles and counts.

Source Data Fig. 5

Elliptical dimensions a and b.

Source Data Fig. 6

Steady-state absorption and fluorescence spectra, time-resolved fluorescence spectra and fit values.

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Gotfredsen, H., Deng, JR., Van Raden, J.M. et al. Bending a photonic wire into a ring. Nat. Chem. 14, 1436–1442 (2022). https://doi.org/10.1038/s41557-022-01032-w

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