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Abstract The optimization of the quantum efficiency of single-molecule light-driven rotary motors typically relies on chemical modifications. While, in isolated conditions, computational methods have been frequently used to design more efficient motors, the role played by the solvent environment has not been satisfactorily investigated. In this study, we used multiscale nonadiabatic molecular dynamics simulations of the working cycle of a 2-stroke photon-only molecular rotary motor. The results, which display dynamics consistent with the available transient spectroscopy measurements, predict a considerable decrease in the isomerisation quantum efficiency in methanol solution with respect to the gas phase. The origin of such a decrease is traced back to the ability of the motor to establish hydrogen bonds with solvent molecules. The analysis suggests that a modified motor with a reduced ability to form hydrogen bonds will display increased quantum efficiency, therefore extending the set of engineering rules available for designing light-driven rotary motors.
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This content will become publicly available on August 12, 2026
Population Dynamics of a Photon-Only Molecular Motor Shows That Mode Synchronization and Transient Binding Determine the Rotary Quantum Efficiency
We present a study of the full rotary cycle of the photon-only rotary motor 3'-(2-methyl-2,3-dihydro-1H-benzo[b]cyclo-penta[d]thiophen-1-ylidene)pyrrolidin-2-one (MTDP) focusing on directionality and quantum efficiency (Φiso). By propagating hundreds of room-temperature quantum-classical trajectories in methanol, we demonstrate that the motor EP → ZP half-cycle exhibits relatively slow dynamics, partial loss of directionality, and low Φiso, while, in contrast, the ZP → EP half-cycle displays faster dynamics, full directionality, and an increased Φiso value. Statistical analyses show that such a dynamical diversity is due to two factors. The first is the presence of a transient binding between the amidic carbonyl group of the rotor and the stereogenic center substituent of the stator in the first half-cycle that is lost in the second half-cycle. The second is a synchronized rotary and ring-inversion motion of the rotor in the second-half cycle that "catalyzes" product formation. It is concluded that such contrasting factors must be considered when designing light-to-mechanical energy transduction molecular devices in general.
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- Award ID(s):
- 2102619
- PAR ID:
- 10647476
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Journal of Chemical Theory and Computation
- Volume:
- 21
- Issue:
- 15
- ISSN:
- 1549-9618
- Page Range / eLocation ID:
- 7503 to 7516
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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