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Roy, Palas, Sardjan, Andy S., Danowski, Wojciech, Browne, Wesley R., Feringa, Ben L. and Meech, Stephen R. 
ORCID: https://orcid.org/0000-0001-5561-2782
(2024)
Substituent effects on first generation photochemical molecular motors probed by femtosecond stimulated Raman.
Journal of Chemical Physics, 161 (7).
ISSN 0021-9606
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Abstract
Unidirectional photochemical molecular motors can act as a power source for molecular machines. The motors operate by successive excited state isomerization and ground state helix inversion reactions, attaining unidirectionality from an interplay of steric strain and stereochemistry. Optimizing the yield of the excited state isomerization reaction is an important goal that requires detailed knowledge of excited state dynamics. Here, we investigate the effect of electron withdrawing and donating substituents on excited state structure and ultrafast dynamics in a series of newly synthesized first generation photochemical molecular motors. All substituents red-shift the absorption spectra, while some modify the Stokes shift and render the fluorescence quantum yield solvent polarity dependent. Raman spectra and density functional theory calculations reveal that the stretching mode of the C=C “axle” in the electronic ground state shows a small red-shift when conjugated with electron withdrawing substituents. Ultrafast fluorescence measurements reveal substituent and solvent polarity effects, with the excited state decay being accelerated by both polar solvent environment and electron withdrawing substituents. Excited state structural dynamics are investigated by fluorescence coherence spectroscopy and femtosecond stimulated Raman spectroscopy. The time resolved Raman measurements are shown to provide structural data specifically on the Franck-Condon excited state. The C=C localized modes have a different substituent dependence compared to the ground state, with the unsubstituted motor having the most red-shifted mode. Such measurements provide valuable new insights into pathways to optimize photochemical molecular motor performance, especially if they can be coupled with high-quality quantum molecular dynamics calculations.
| Item Type: | Article |
|---|---|
| Additional Information: | Data Availability: The data that support the findings are mainly included in the article and its supplementary material or otherwise available from the authors on reasonable request. Funding information: Financial support provided by The Netherlands Ministry of Education, Culture and Science (Gravity Program 024.001.035 to WRB, BLF) and the UKRI EPSRC (grants EP/R042357/1, EP/J009148/1 to SRM) is acknowledged. |
| Uncontrolled Keywords: | physics and astronomy(all),physical and theoretical chemistry,2*,specialist ,/dk/atira/pure/subjectarea/asjc/3100 |
| Faculty \ School: | Faculty of Science > School of Chemistry (former - to 2024) |
| UEA Research Groups: | Faculty of Science > Research Groups > Centre for Photonics and Quantum Science Faculty of Science > Research Groups > Chemistry of Light and Energy |
| Related URLs: | |
| Depositing User: | LivePure Connector |
| Date Deposited: | 25 Jul 2024 11:30 |
| Last Modified: | 30 Oct 2024 00:51 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/96025 |
| DOI: | 10.1063/5.0216442 |
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