Single molecular rotor at the nanoscale

The design of a monomolecular engine such as a rotating motor first require s the preparation of a semi-classical rotating motion of the rotor part of the engine. We show that this can be achieved either by a careful quantum c ontrol of the time evolution of an initially prepared rotating quantum wave packet or by controlling the interaction of the rotor (or stator) with a r eservoir. This second alternative is illustrated experimentally through the realization of the rotary motion of a hexa-tert-butyl-decacyclene molecule self-assembled in an homomolecular cavity on an ultraclean Cu(100) surface . The conditions to transform such a molecular rotor into a motor with a gi ven motive power are also discussed.