Ultrafast Excited State Dynamics in a First Generation Photomolecular Motor

Andy S. Sardjan, Palas Roy, Wojciech Danowski, Giovanni Bressan, Laura Nunes dos Santos Comprido, Wesley R. Browne, Ben. L. Feringa*, Stephen R. Meech

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

3 Citations (Scopus)
59 Downloads (Pure)

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.

Original languageEnglish
Pages (from-to) 594-599
Number of pages7
JournalChemphyschem
Volume21
Issue number7
Early online date23-Jan-2020
DOIs
Publication statusPublished - Apr-2020

Keywords

  • excited state
  • fluorescence
  • coherence
  • molecular motor
  • photochemistry
  • ultrafast dynamics
  • MOLECULAR MOTORS
  • UNIDIRECTIONAL ROTATION
  • VIBRATIONAL COHERENCE
  • PHOTOISOMERIZATION
  • ACCELERATION
  • SPEED

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