  We introduce some basic concepts for designer molecules with functional units
which are driven by entropic rather than energetic forces. This idea profits
from the mechanically interlocked nature of topological molecules such as
catenanes and rotaxanes, which allows for mobile elements whose accessible
configuration space gives rise to entropic intramolecular forces. Such
entropy-driven designer molecules open the possibility for externally
controllable functional molecules and nanomechanical devices.
