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Mapping the Excited‐State Potential Energy Surface of a Photomolecular Motor
Author(s) -
Hall Christopher R.,
Browne Wesley R.,
Feringa Ben L.,
Meech Stephen R.
Publication year - 2018
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201802126
Subject(s) - excited state , metastability , femtosecond , potential energy surface , femtochemistry , ground state , spectroscopy , ultrafast laser spectroscopy , molecular physics , reaction coordinate , chemical physics , chemistry , molecular motor , atomic physics , photochemistry , materials science , molecule , laser , physics , nanotechnology , optics , computational chemistry , organic chemistry , quantum mechanics
A detailed understanding of the operation and efficiency of unidirectional photomolecular rotary motors is essential for their effective exploitation in molecular nanomachines. Unidirectional motion relies on light‐driven conversion from a stable ( 1 a ) to a metastable ( 1 b ) conformation, which then relaxes through a thermally driven helix inversion in the ground state. The excited‐state surface has thus far only been experimentally characterised for 1 a . Here we probe the metastable, 1 b , excited state, utilising ultrafast transient absorption and femtosecond stimulated Raman spectroscopy. These reveal that the “dark” excited‐state intermediate between 1 a and 1 b has a different lifetime and structure depending on the initial ground‐state conformation excited. This suggests that the reaction coordinate connecting 1 a to 1 b differs to that for the reverse photochemical process. The result is contrasted with earlier calculations.