FROM CHEMICAL TOPOLOGY TO MACHINES AND MOTORS AT THE MOLECULAR LEVEL

Damien JOUVENOT

Laboratoire de Chimie Organo-Minérale, Institut Le Bel, Université Louis Pasteur,

4, rue Blaise Pascal, 67070 Strasbourg , France E-mail : sauvage@chimie.u-strasb.fr

Catenanes (interlocking rings) and knots represent attractive synthetic challenges for molecular chemists. Besides their topological properties, these systems can be regarded as works of art at the nanometer scale. The creation of such complex molecules also demonstrates that synthetic chemistry is now powerful enough to tackle problems whose complexity is sometimes reminiscent of biology, although the elaboration of molecular ensembles displaying properties as complex as biological assemblies is still a long-term challenge.

The field of artificial molecular machines and motors has experienced a spectacular development in the course of the last decade, in relation with biological motors (as mimics) or information storage and processing at the molecular level (toward molecule-based computers). These systems are multicomponent assemblies undergoing large-amplitude geometrical changes or leading to the locomotion of one of the components, under the action of an external stimulus.

Threaded or interlocking rings are ideally suited to the construction of fully artificial molecular motors. If a ring is threaded onto a rod, it can either rotate around the axle or undergo a translation movement. Similarly, in catenanes, a ring can glide at will and spin within another ring.

Several examples or such compounds have been elaborated and studied in recent years. In particular, our group has proposed several molecular assemblies acting as "machines". They are based on transition metal complexes and the systems are set in motion by sending an electrochemical, a photochemical or a chemical signal. A recent contribution describes a doubly threaded compound which can be contracted or stretched at will. It is thus reminiscent of skeletal muscles. Another approach is based on dissociative excited states such as the ligand-field state of Ru(bipy)₃²⁺ derivatives. New rotaxanes (rings threaded by a molecular axis) and catenanes have been constructed around an octahedral centre (Ru). These systems can be set in motion by sending a photonic signal to the molecule.

In a long-term prospective, the field may find applications in relation to information storage and processing at the molecular level. It can also be envisaged that microrobots be built, using molecular components able to move the various parts of an articulated backbone.