Population and coherence dynamics in large conjugated porphyrin nanorings

Bressan, Giovanni ORCID: https://orcid.org/0000-0001-7801-8495, Jirasek, Michael, Roy, Palas, Anderson, Harry L., Meech, Stephen R. ORCID: https://orcid.org/0000-0001-5561-2782 and Heisler, Ismael A. (2022) Population and coherence dynamics in large conjugated porphyrin nanorings. Chemical Science, 13 (33). pp. 9624-9636. ISSN 2041-6520

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In photosynthesis, nature exploits the distinctive electronic properties of chromophores arranged in supramolecular rings for efficient light harvesting. Among synthetic supramolecular cyclic structures, porphyrin nanorings have attracted considerable attention as they have a resemblance to naturally occurring light-harvesting structures but offer the ability to control ring size and the level of disorder. Here, broadband femtosecond transient absorption spectroscopy, with pump pulses in resonance with either the high or the low energy sides of the inhomogeneously broadened absorption spectrum, is used to study the population dynamics and ground and excited state vibrational coherence in large porphyrin nanorings. A series of fully conjugated, alkyne bridged, nanorings constituted of between ten and forty porphyrin units is studied. Pump-wavelength dependent fast spectral evolution is found. A fast rise or decay of the stimulated emission is found when large porphyrin nanorings are excited on, respectively, the high or low energy side of the absorption spectrum. Such dynamics are consistent with the hypothesis of a variation in transition dipole moment across the inhomogeneously broadened ground state ensemble. The observed dynamics indicate the interplay of nanoring conformation and oscillator strength. Oscillatory dynamics on the sub-ps time domain are observed in both pumping conditions. A combined analysis of the excitation wavelength-dependent transient spectra along with the amplitude and phase evolution of the oscillations allows assignment to vibrational wavepackets evolving on either ground or excited states electronic potential energy surfaces. Even though porphyrin nanorings support highly delocalized electronic wavefunctions, with coherence length spanning tens of chromophores, the measured vibrational coherences remain localised on the monomers. The main contributions to the beatings are assigned to two vibrational modes localised on the porphyrin cores: a Zn-N stretching mode and a skeletal methinic/pyrrolic C-C stretching and in-plane bending mode.

Item Type: Article
Additional Information: Acknowledgements: G. B., P. R., I. A. H. and S. R. M. acknowledge support from the Engineering and Physical Sciences Research Council under Awards No. EP/J009148/1, EP/J007161/1 and EP/J021431/1. H. L. A. acknowledges support from the ERC (grant 320969) and EPSRC (EP/M016110/1). M. J. thanks Oxford University for a Scatchard European Scholarship. The authors would like to thank Dr Dale Green for the helpful discussions.
Uncontrolled Keywords: chemistry(all),3*,good work, good journal, low impact ,/dk/atira/pure/subjectarea/asjc/1600
Faculty \ School: Faculty of Science > School of Chemistry
UEA Research Groups: Faculty of Science > Research Groups > Chemistry of Light and Energy
Faculty of Science > Research Groups > Centre for Photonics and Quantum Science
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Depositing User: LivePure Connector
Date Deposited: 13 Jul 2022 09:30
Last Modified: 28 Jul 2023 03:47
URI: https://ueaeprints.uea.ac.uk/id/eprint/86086
DOI: 10.1039/D2SC01971J


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