Ultrafast Excited State Dynamics in a First Generation Photomolecular Motor

Sardjan, Andy S., Roy, Palas, Danowski, Wojciech, Bressan, Giovanni, Nunes dos Santos Comprido, Laura, Browne, Wesley R., Feringa, Ben L. and Meech, Stephen R. (2020) Ultrafast Excited State Dynamics in a First Generation Photomolecular Motor. ChemPhysChem, 21 (7). pp. 594-599. ISSN 1439-4235

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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: 25 Feb 2022 01:07
URI: https://ueaeprints.uea.ac.uk/id/eprint/73709
DOI: 10.1002/cphc.201901179

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