"Transmission of different movements involving power conversion processes is essential for the operation of movable machines and robots," Kazushi Kinbara of the University of Tokyo told nanotechweb.org. "For example, automobiles are driven by the conversion of a piston action into a rotary motion, for which multiple different movable components are integrated and interlocked with one another. However, this conception has never been realized in molecular machines [until now]."

Kinbara and colleagues used a molecule comprising a ferrocene (Fe(C5H5)2 component, an azobenzene strap and two zinc porphyrin units. Each end of the azobenzene strap was linked to one of the ferrocene's cyclopentadienyl rings, which in turn linked to a zinc porphyrin unit.

Bathing the molecule in ultraviolet light caused the azobenzene strap to move from its trans form to its cis form, in a process known as photoisomerization. This rotated the ferrocene's cyclopentadienyl rings, which in turn changed the relative position of the two porphyrin units, or "pedals". Applying visible light reversed the process and moved the pedals back to their original positions.

A binding site on each of the pedals enabled them to form a stable complex with a guest rotor molecule. As the pedals moved with respect to each other, this guest molecule was twisted.

"The most significant point is that molecular motion could be transferred through non-covalent bonds," said Kinbara. "Motions of two different molecules occur synchronously."

Now the researchers, who reported their results in Nature, are working to integrate multiple molecular machines into "huge molecular machineries".