All-Photochemical Rotation of Molecular Motors with a Phosphorus Stereoelement

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Photochemistry

Background:

• Unidirectional molecular rotation typically relies on combined photochemical and thermal steps.
• Purely photochemical rotary cycles in molecular motors are uncommon.
• Overcrowded alkenes are a common motif in molecular motor design.

Purpose of the Study:

• To develop novel second-generation molecular motors capable of all-photochemical unidirectional rotation.
• To investigate the influence of a phosphorus stereocenter on molecular motor behavior.
• To achieve crystallographic characterization of the complete rotational cycle of molecular motors.

Main Methods:

• Synthesis of three new second-generation molecular motors with a phosphorus center.
• Photochemical isomerization studies to analyze rotary behavior.
• Kinetic analysis and computational modeling to elucidate the mechanism.
• X-ray crystallography to determine the structures of all diastereomeric states.

Main Results:

• The new molecular motors demonstrate all-photochemical unidirectional rotation.
• All four diastereomeric states interconvert exclusively through photochemical means.
• The first X-ray crystal structures of all diastereomeric states for a full 360° rotation of overcrowded-alkene-based motors were obtained.
• Thermal inversion of the phosphorus stereocenter provides a shortcut in the rotational cycle.

Conclusions:

• The developed molecular motors represent a significant advancement in achieving purely photochemical rotary cycles.
• The phosphorus stereocenter introduces unique axial chirality and enables novel mechanistic pathways.
• Crystallographic insights provide unprecedented atomic-level understanding of molecular motor operation.
• The thermal epimerization offers a new strategy for controlling molecular motor function.