Tunneling Dendrimers. Enhancing Charge Transport through Insulating Layer Using Redox Molecular Objects

Abstract

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.

Why is Ferrocene so Exceptional?

“…[301,302] Various other ferrocene-containing dendrimers have been reported, their electrochemical properties providing useful information on interfacial electron-transfer properties and redox-recognition features. [303][304][305][306][307][308] Giant ferrocene-terminated dendrimers containing up to 15000 ferrocene or pentamethylferrocene termini were synthesized, and both the ferrocene and ferricinium forms were characterized by electronic microscopy with the termini showing the redox "breath-ing" like molecular machines between the reduced and oxidized forms, the latter experiencing coulombic repulsion between charges that expanded the polycationic metallodendrimer size [Equation (8)]. [305] (8) Click ferrocenyl dendrimers of zeroth (G0), first (G1), and second generation (G2), containing 9, 27, and 81 triazolylferrocenyl termini, respectively, were shown to stabilize highly catalytically active PdNPs through the intradendritic triazole ligands.…”

Nanofabrication and Electrochemical Characterization of Self-Assembled Monolayers Sandwiched between Metal Nanoparticles and Electrode Surfaces

“…19 This effect has been observed for several types of conducting nanostructures including metal nanoparticles, 19 carbon nanotubes, 20 graphene sheets, 21 quantum dots 22 and even purely molecular objects containing a large number of redox centers. 23 This restoration of the electron transfer has been attributed to a relay station effect of the conducting nanostructures that facilitates the electronic coupling between the underlying electrode and the redox probe. 24 Therefore, when the conducting nanostructure is attached to the SAM-modified electrode, the electron transfer process involves two consecutive steps: (i) electron transfer between the underlying electrode and the conducting nanostructures, mediated by electron tunneling through the organic layer, and (ii) electron transfer between the conducting nanostructures and the redox probe, which is the rate-limiting step with regard to charge transfer within these particular systems.…”

Molecular Sieving and Current Rectification Properties of Thin Organic Films

“…The number of points per bohr3 is 100 with a cutoff= 10-4 and used with the "Vol=Tight" option for a better accuracy that is better than 10%. 41 the organic layer, a 2 nm-film should allow the electron transfer by tunneling 44,45 and, with this value of thickness, differentiate between direct electron transfer by pinholes or defects by only using outer-spbere redox probes may be difficult. Thus, the discussion will be focus on the electrochemical behavior of the thicker 4 nm-aryldiazonium layer since, in this case, the tunneling electron transfer can be neglected.…”