Optical molecular switches
We have reported the electron-transport properties of a new photoaddressable molecular switch. The switching process relies on a new concept based on linear π-conjugated dynamic systems, in which the geometry and, hence, the electronic properties of an oligothiophene chain can be reversibly modified by the photochemical trans−cis isomerization of an azobenzene unit fixed in a lateral loop. [S. Lenfant et al., J. Phys. Chem. C (2017)].
We have also designed and synthesized a new azobenzene-thiophene molecular switch exhibiting a high “on/off” conductance ratio up to 7,000 (C-AFM on SAMs). [K. Smaali et al., ACS Nano (2010)].
Main coll. : P. Blanchard, J. Roncali (CNRS, Moltech-Anjou, U. Angers); J. Cornil (LCNM, U. Mons, Belgium); C. van Dyck (Dept. Chem., Northwestern Univ., Evanston, USA); A. Rochefort (Ecole Polytechnique Montréal, Quebec, Canada).
Chemical molecular switches
We demonstrate that the conductance switching of benzo-bis(imidazole) molecules upon protonation depends on the lateral functional groups. The protonated H-substituted molecule shows a higher conductance than the neutral one, explained by a reduction of the LUMO-HOMO gap. The opposite is observed for a molecule laterally functionalized by amino-phenyl groups, consistent with a shift of HOMO, which reduces the density of states at the Fermi energy [H. Audi et al., Nanoscale (2020)].
Main coll. : O. Siri, H. Klein (CINAM, CNRS, Marseille, France), I.M. Grace, C.J. Lambert (Physics Dept., Lancaster Univ. UK).
We report how the electron transport (C-AFM measurements and first-principle calculations) through a solid-state metal/Gly-Gly-His tripeptide (GGH) monolayer/metal junction are modified by the GGH complexation with Cu2+ ions. Complexed copper to low density GGH-monolayer induces a new gap state slightly above the Au Fermi energy that is absent in the high density monolayer. [E. Mervinetsky et al., J. Phys. Chem. C (2019)]
Main Coll. : S. Yitzchaik (Institute of Chemistry, The Hebrew University of Jerusalem, Israel); R. Gutierrez (Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, Germany).
We report on the surface immobilization by double fixation on gold surface of a dithiol quaterthiophene derivatized with a crown-ether loop. Upon complexation of Pb2+ ions, the conductance of the molecular junction is increased by a factor up to 1.6×103, which is explained by a decrease of about 0.4 eV of the position of the molecular orbital involved to the electron transport with respect of the electrode Fermi energy. [T.K. Tran et al., Adv. Mater. (2013)]
Main coll.: P. Blanchard, J. Roncali (CNRS, Moltech-Anjou, U. Angers).