IN NATURE, CONTROL OF CHIrality at different hierarchical levels is manifested in processes such as protein folding and enzyme catalysis. Efforts at achieving similar control in synthetic system are aimed not only at gaining insight into how nature does it but also at applying such control to the design of reactions and materials. Researchers have now reported a reversible, photoresponsive, self-assembling system in which chiral information is exchanged between molecular and supramolecular units { Science , 304, 278 (2004)}. Designed by chemistry professors Ben L. Feringa and Jan H. van Esch at the University of Groningen, the Netherlands, and coworkers, the system is based on a dithienylethene unit functionalized with chiral amide groups. In the presence of light, the molecules can switch between two states: ring-open or ring-closed. Because of the flexibility of the dithienylethene core, the open form can assume either a left- or right-handed helical conformation. When a solution of ...