The article "Light-driven monodirectional molecular rotor" by Koumura et al. (1999) reports the development of a light-driven, monodirectional molecular rotor. The rotor is a chiral, helical alkene that undergoes repetitive, unidirectional rotation around a central carbon-carbon double bond. Each 360° rotation involves four discrete isomerization steps activated by ultraviolet light or temperature changes. The key features that enable this unidirectional behavior include axial chirality and the presence of two chiral centers. The molecular rotor, (3R,3'R)-(P,P)-trans-1, undergoes two light-induced cis-trans isomerizations, each associated with a 180° rotation, followed by thermally controlled helicity inversions that block reverse rotation. The study demonstrates that the energy barriers for these steps can be adjusted, making the chiral alkenes potential components for light-driven molecular machinery. The authors also provide spectroscopic evidence and detailed experimental data to support their findings.The article "Light-driven monodirectional molecular rotor" by Koumura et al. (1999) reports the development of a light-driven, monodirectional molecular rotor. The rotor is a chiral, helical alkene that undergoes repetitive, unidirectional rotation around a central carbon-carbon double bond. Each 360° rotation involves four discrete isomerization steps activated by ultraviolet light or temperature changes. The key features that enable this unidirectional behavior include axial chirality and the presence of two chiral centers. The molecular rotor, (3R,3'R)-(P,P)-trans-1, undergoes two light-induced cis-trans isomerizations, each associated with a 180° rotation, followed by thermally controlled helicity inversions that block reverse rotation. The study demonstrates that the energy barriers for these steps can be adjusted, making the chiral alkenes potential components for light-driven molecular machinery. The authors also provide spectroscopic evidence and detailed experimental data to support their findings.