Photophysics of first-generation photomolecular motors: Resolving roles of temperature, friction, and medium polarity

Steve Meech, Palas Roy, Andy S. Sardjan, Wojciech Danowski, Wesley R. Browne, Ben L. Feringa

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)
11 Downloads (Pure)


Light-driven unidirectional molecular rotary motors have the potential to power molecular machines. Consequently, optimizing their speed and efficiency is an important objective. Here, we investigate factors controlling the photochemical yield of the prototypical unidirectional rotary motor, a sterically overcrowded alkene, through detailed investigation of its excited-state dynamics. An isoviscosity analysis of the ultrafast fluorescence decay data resolves friction from barrier effects and reveals a 3.4 ± 0.5 kJ mol−1 barrier to excited-state decay in nonpolar media. Extension of this analysis to polar solvents shows that this barrier height is a strong function of medium polarity and that the decay pathway becomes near barrierless in more polar media. Thus, the properties of the medium can be used as a route for controlling the motor’s excited-state dynamics. The connection between these dynamics and the quantum yield of photochemical isomerization is probed. The photochemical quantum yield is shown to be a much weaker function of solvent polarity, and the most efficient excited-state decay pathway does not lead to a strongly enhanced quantum yield for isomerization. These results are discussed in terms of the solvent dependence of the complex multidimensional excited-state reaction coordinate.
Original languageEnglish
Pages (from-to)1711-1719
Number of pages9
JournalThe Journal of Physical Chemistry A
Issue number8
Early online date19 Feb 2021
Publication statusPublished - 4 Mar 2021

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