Locked synchronous rotor motion in a molecular motor

[slochower]

@doi:10.1126/science.aam8808

Biological molecular motors translate their local directional motion into ordered movement
of other parts of the system to empower controlled mechanical functions. The design of analogous geared systems that couple motion in a directional manner, which is pivotal for molecular machinery operating at the nanoscale, remains highly challenging. Here, we report a molecular rotary motor that translates light-driven unidirectional rotary motion to controlled movement of a connected biaryl rotor. Achieving coupled motion of the distinct parts of this multicomponent mechanical system required precise control of multiple kinetic barriers for isomerization and synchronous motion, resulting in sliding and rotation during a full rotary cycle, with the motor always facing the same face of the rotor.

[slochower]

I've read this through a few times before, but I'm still missing some of the chemistry that's going on. I'm a little fuzzy on whether this is a second generation motor or something else. They write "our design was based on a second-generation molecular motor."

[slochower]

Here they've added a naphthalene substituent (two fused rings) as the rotor. During a single rotation, one side of the aryl rotor (I think this is still referring to the naphthalene) continuously faces the lower half of the molecular motor. This is what they mean by "synchronous rotation." This is achieved by preventing free rotation of naphthalene (I think this is what they mean by biaryl rotation (BR)).

[slochower]

1. Photochemical: the molecular motor (MM) is forced into a metastable form. The BR moiety and the fluorine lower half are adjusted relative to each other.
2. Thermal: I believe this is the helix inversion. The BR angle changes but full rotation is blocked.
3. Photochemical: The angel of the upper half is significantly shifted, moving the BR moiety.
4. Thermal: another helix inversion, maybe.