Switchable Molecular Tweezers – SMARTEES

The drive to miniaturize devices has led to a variety of molecular machines inspired by their macroscopic counterparts such as molecular motors, switches, nanovehicles and tweezers. Even if the control of motion at the molecular level has been mastered by some machines, the reversible control of properties at the molecular level remains a challenge. Supramolecular chemistry seems to be a key element to build switchable systems. Molecular tweezers are synthetic molecular receptors with an open cavity defined by two interaction sites for substrate binding, bridged by a spacer. Most of the existing molecular tweezers are static (molecular clips) and have been used for molecular recognition applications with rare examples being switchable. The aim of this proposal is to design switchable molecular tweezers to control physical or chemical properties at the molecular level via a mechanical motion, which is an innovative approach.
Our system is based on a unit switchable through metal coordination (terpyridine) that is functionalized by different metallic salen complexes presenting magnetic, luminescent or catalytic properties depending on the metal center. In the free form the tweezers adopt an open 'W' shaped geometry that is converted to a closed 'U' shaped one by metal coordination on the terpy ligand. The key feature of this approach is to control the distance between two functional units via a mechanical motion to trigger a drastic modification of their properties via a direct interaction or via a substrate. In a first time, luminescent tweezers based on a platinum complex will be synthetized and optimized for molecular recognition and / or luminescence switching. The luminescent complexes should act as a probe when the substrates are intercalated. The switching and recognition properties will be studied by a combination of NMR, UV-Vis and fluorescence spectroscopy. Once the mechanical motion with the diamagnetic luminescent tweezers has been mastered, paramagnetic metals will be incorporated on the same platform in the salen unit. We expect to switch the magnetic properties of the system between the open form, where the metallic center should be non-interacting and the closed form where an interaction through space or modulation by bridging ligands should occur. By incorporating Single Molecule Magnets (SMM) or high spin complexes, large switching effects should be obtained upon mechanical motion. The tweezers will also be tested as an allosteric catalyst in cooperative catalytic reactions. A difference of activity is expected between the open form where the two complexes are far apart and act as monomeric species with low activity and a cooperative effect in the closed form where the two salen complexes are brought in close proximity. In the long term, the objectives are to incorporate these systems into functional devices and use the versatility of the design to tackle transduction of molecular motion from the microscopic level to micro or mesoscopic scales.
The originality of this project is the use of the mechanical motion of a nanomachine to control physical or chemical properties at the nanoscale. The modularity and versatility of our design promises a wide scope for applications in multiple fields such as information storage, smart materials and catalysis. For this project, we have established a multidisciplinary consortium with complementary expertise in synthesis, photophysics, magnetism and catalysis. It will allow the young PI to establish his own research.