Fast response dry-type artificial molecular muscles with [c2]daisy chains

Hierarchically organized myosin and actin filaments found in biological systems exhibit contraction and expansion behaviours that produce work and force by consuming chemical energy. Inspired by these naturally occurring examples, we have developed photoresponsive wet- and dry-type molecular actuators built from rotaxane-based compounds known as [c2]daisy chains (specifically, [c2]AzoCD(2) hydrogel and [c2]AzoCD(2) xerogel). These actuators were prepared via polycondensation between four-armed poly(ethylene glycol) and a [c2]daisy chain based on alpha-cyclodextrin as the host component and azobenzene as a photoresponsive guest component. The light-induced actuation arises from the sliding motion of the [c2]daisy chain unit. Ultraviolet irradiation caused the gels to bend towards the light source. The response of the [c2]AzoCD(2) xerogel, even under dry conditions, is very fast (7 degrees every second), which is 10,800 times faster than the [c2]AzoCD(2) hydrogel (7 degrees every 3 h). In addition, the [c2]AzoCD(2) xerogel was used as a crane arm to lift an object using ultraviolet irradiation to produce mechanical work.