Charge transport through an insulating layer was probed using ferrocenyl-terminated dendrimers and scanning electrochemical microscopy. Experiments show that the passage through the layer is considerably enhanced when the transferred charges are brought globally to the surface by the ferrocenyl dendrimer instead of a single ferrocene molecule. This result shows that charge tunneling through an insulator could be promoted by a purely molecular nano-object.

International audienceElectrochemical properties of carbon surfaces modified by a covalently attached redox monolayer (alkyl-ferrocenyl) have been investigated in three different classical room temperature ionic liquids (RTILs): BMIPF6, BMINTf2, Me3BuNNTf2, and in two common molecular solvents (ethanol and CH2Cl2) for evidencing special aspects of the electronic transfer in RTILs. If the redox activity and the stability of the layer are globally preserved in the RTILs, a considerable decrease of the amount of active redox groups is observed when the layer is examined in the RTILs. The oxidation potentials are only slightly higher in the RTILs contrarily to the charge transfer kinetics that decrease by a factor of 10–20 as measured for the rates between the attached redox moieties and the substrate. These behaviors that appear as possible limitations for practical applications of such systems in RTILs could be ascribed to specific ionic associations and a large reorganization of the layer during its charging process

International audienceCharge-transfer complexes involving tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) derivatives are engineered in a 2D arrangement onto a carbon surface through the exposure of immobilized TTF units to TCNQ compounds. TTF molecules were immobilized as robust monolayers on carbon surfaces using the electrografting method followed by a click chemistry coupling. When the TTF monolayer is exposed to TCNQ TCNQF(2) (2,5-difluoroTCNQ), and TCNQF4 (2,3,5,6-tetrafluoro-TCNQ), strong donor acceptor complexes are formed onto the surface. A considerable decrease of the electrochemical response accompanies the formation of the charge-transfer complex. This observation is rationalized by the analysis of original crystal samples using an ultramicroelectrode cavity, confirming that charge transfer complexes are electrochemically silent. A fine control of the degree of charge transfer with the judicious choice of different acceptors is evidenced through electrochemical and X-ray photoelectron spectroscopy (XPS) measurements. Thus, donor acceptor complexes of different natures are formed. A fully ionic charge-transfer complex is formed upon exposure of the TTF monolayer to the more oxidizing TCNQF(4), while a neutral complex is obtained after exposure to the less oxidizing TCNQ, Exposition of the TTF monolayers to the intermediate TCNQF(2) yields a mixture of neutral-ionic systems. These donor acceptor interactions that fully mimic those described in the solid state are rarely described in such a 2D arrangement, with systems being directly wired to an electrode