Ultrafast excited state dynamics in a first generation photomolecular motor

Sardjan, Andy S., Roy, Palas, Danowski, Wojciech, Bressan, Giovanni ORCID: https://orcid.org/0000-0001-7801-8495, Nunes dos Santos Comprido, Laura, Browne, Wesley R., Feringa, Ben L. and Meech, Stephen R. ORCID: https://orcid.org/0000-0001-5561-2782 (2020) Ultrafast excited state dynamics in a first generation photomolecular motor. ChemPhysChem, 21 (7). pp. 594-599. ISSN 1439-4235

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Abstract

Efficient photomolecular motors will be critical elements in the design and development of molecular machines. Optimisation of the quantum yield for photoisomerisation requires a detailed understanding of molecular dynamics in the excited electronic state. Here we probe the primary photophysical processes in the archetypal first generation photomolecular motor, with sub-50 fs time resolved fluorescence spectroscopy. A bimodal relaxation is observed with a 100 fs relaxation of the Franck-Condon state to populate a red-shifted state with a reduced transition moment, which then undergoes multi-exponential decay on a picosecond timescale. Oscillations due to the excitation of vibrational coherences in the S 1 state are seen to survive the ultrafast structural relaxation. The picosecond relaxation reveals a strong solvent friction effect which is thus ascribed to torsion about the C−C axle. This behaviour is contrasted with second generation photomolecular motors; the principal differences are explained by the existence of a barrier on the excited state surface in the case of the first-generation motors which is absent in the second generation. These results will help to provide a basis for designing more efficient molecular motors in the future.

Item Type: Article
Uncontrolled Keywords: acceleration,molecular motors,photoisomerization,speed,unidirectional rotation,vibrational coherence,coherence,excited state,fluorescence,molecular motor,photochemistry,ultrafast dynamics
Faculty \ School: Faculty of Science > School of Chemistry
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Depositing User: LivePure Connector
Date Deposited: 21 Jan 2020 10:48
Last Modified: 22 Oct 2022 05:43
URI: https://ueaeprints.uea.ac.uk/id/eprint/73709
DOI: 10.1002/cphc.201901179

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