Smart materials: A light touch (pp 778-781; N&V)

Researchers have developed crystals that will change their shape repeatedly when exposed to different types of light. The discovery may aid the development of light-driven actuators — mechanical devices that move or control things.
The molecular crystals, developed by Masahiro Irie and colleagues, are based on a particular type of light-absorbing molecule and range from 10 to 100 micrometres in size. When ultraviolet light is shone on one type of crystal, it changes shape from a square to a lozenge. But when the same crystal is exposed to visible light, it undergoes another mechanical deformation to change back to its original form. When put in the spotlight, a rod-shaped crystal of the material attached to a surface will even oblige and use this effect to 'bat' away a micrometre-sized gold particle.
The system is stable and responds quickly, within microseconds. Previous light-responsive systems, made from liquid crystals or polymer gels, can change shape but the effect takes seconds or longer and the deformed states are unstable. And the beauty of using light as a stimulus is that it offers the intriguing prospect of actuators that can be operated remotely.
CONTACT
Masahiro Irie (Rikkyo University, Tokyo, Japan)
Tel: +81 3 3985 2397; E-mail: irie@cstf.kyushu-u.ac.jp
J. Michael McBride (Yale University, New Haven, CT, USA) N&V author
Tel: +1 203 432 3926; E-mail: j.mcbride@yale.edu


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