One promising solution is to load them into tough, porous crystals known as metal-organic frameworks (MOFs), which protect the switches and organize them into a precise 3D array.
Earlier this year, Robert Schurko and Stephen Loeb of the University of Windsor, Canada, showed that they could pack about 10 a different MOF that contained switchable rotaxanes.
“In 15 years' time,” says Leigh, “I think they will be seen as a core part of chemistry and materials design.” Getting there will not be easy.
Researchers must learn how to make billions of molecular machines work in concert to produce measurable macroscopic effects such as changing the shape of a material so that it acts as an artificial muscle.
“We need to convince them that these molecules are really exciting.” Many of today's molecular machines trace their origins to a relatively simple device built in 1991 by Fraser Stoddart, a chemist now at Northwestern University in Evanston, Illinois.