Molecular "Wankel Engine" Driven By Photons

Molecular "Wankel Engine" Driven By Photons: A couple of year ago, chemists discovered that groups of 13 or 19 boron molecules form into concentric rings that can rotate independently, rather like the piston in a rotary Wankel engine. Because of this, they quickly picked up the moniker "molecular Wankel engines". The only question was how to power them.

Now Zhang and buddies have calculated that this should be remarkably easy--just zap them with circularly polarised infrared light. That sets the inner ring counter-rotating relative the outer one, like a Wankel engine...
What makes this one special is that the polarised light doesn't excite the molecule's electronic ground state,  leaving it free to be chemically active.