Ultrafast dynamics in the power stroke of a molecular rotary motor.
Light-driven molecular motors convert light into mechanical energy through excited-state reactions. Unidirectional rotary molecular motors based on chiral overcrowded alkenes operate through consecutive photochemical and thermal steps. The thermal (helix inverting) step has been optimized successfully through variations in molecular structure, but much less is known about the photochemical step, which provides power to the motor. Ultimately, controlling the efficiency of molecular motors requires a detailed picture of the molecular dynamics on the excited-state potential energy surface. Here, we characterize the primary events that follow photon absorption by a unidirectional molecular motor using ultrafast fluorescence up-conversion measurements with sub 50 fs time resolution. We observe an extraordinarily fast initial relaxation out of the Franck-Condon region that suggests a barrierless reaction coordinate. This fast molecular motion is shown to be accompanied by the excitation of coherent excited-state structural motion. The implications of these observations for manipulating motor efficiency are discussed.
School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
Jamie
J
Conyard
Kiri
K
Addison
Ismael A
IA
Heisler
Arjen
A
Cnossen
Wesley R
WR
Browne
Ben L
BL
Feringa
Stephen R
SR
Meech
D005449:Fluorenes / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D007536:Isomerism; D008027:Light; D056004:Molecular Dynamics Simulation; D013059:Spectrum Analysis, Raman; D013997:Time Factors
D005449:Fluorenes; D005456:Fluorescent Dyes