Communication: Control of the rotation of the interlocked rings in catenanes through external stimuli is key to the development of these molecules as components in nanoscale devices such as molecular switches. shuttles, and information storage systems. Here the Linear and unanticipated second-order nonlinear optical properties of vacuum-evaporated thin films of a benzylic amide [2]catenane, consisting of two identical 26-membered macrocyclic rings, are reported. Electro-optic measurements provide evidence that the catenane rings rotate at least partially in the solid state on application on an external, time-dependent electric field.