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Ultrafast Excited State Dynamics in a First Generation Photomolecular Motor

Authors :
Stephen R. Meech
Giovanni Bressan
Ben L. Feringa
Wojciech Danowski
Andy S. Sardjan
Laura Nunes Dos Santos Comprido
Palas Roy
Wesley R. Browne
Molecular Inorganic Chemistry
Synthetic Organic Chemistry
Stratingh Institute of Chemistry
​Basic and Translational Research and Imaging Methodology Development in Groningen (BRIDGE)
Source :
Chemphyschem, 21(7), 594-599. WILEY-V C H VERLAG GMBH, Chemphyschem
Publication Year :
2020
Publisher :
Wiley, 2020.

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 S1 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.<br />Generation conflict? The excited state dynamics of first‐generation molecular motors are studied by means of ultrafast time resolved fluorescence. A 100 fs structural reorganization in the excited state is followed by a slower excited state relaxation, which is influenced by solvent viscosity. The decay is accompanied by coherent vibrational excitation of modes in the excited electronic state. The observed behaviour is contrasted with that of the second‐generation motors.

Details

ISSN :
14397641 and 14394235
Volume :
21
Database :
OpenAIRE
Journal :
ChemPhysChem
Accession number :
edsair.doi.dedup.....00426fb8cfba1f0f9521236df82631fa
Full Text :
https://doi.org/10.1002/cphc.201901179