Shaped by the light Some materials will change size or shape upon light irradiation. Such triggering of mechanical deformations without direct contact offers the intriguing prospect of actuators that can be operated remotely. But the light-deformable polymers and gels developed so far all respond relatively slowly and become unstable after deformation. A new material developed by Kobatake et al . avoids these shortcomings: the molecular crystals, based on diarylethene chromophores and with sizes ranging from 10 to 100 µm, can be switched rapidly and reversibly between two different stable states by irradiation with ultraviolet and visible light, respectively. And when put in the spotlight, a rod-shaped crystal of the material attached to a surface can even 'bat' away a tiny gold particle. Video streams of the crystals in action are online at http://www.nature.com/nature .

An excited state energy migration was found to compete with a photocyclization reaction in the single crystal of 1,2- bis(2,4-dimethyl-3-thienyl)perfluorocyclopentene.