Direct Measurement of Electron Transfer in Nanoscale Host–Guest Systems: Metallocenes in Carbon Nanotubes

Abstract

Electron transfer processes play a significant role in host-guest interactions and determine physicochemical phenomena emerging at the nanoscale that can be harnessed in electronic or optical devices as well as biochemical and catalytic systems. We have developed a novel method for qualifying and quantifying the electronic doping of single walled carbon nanotubes (SWNT) using electrochemistry and have established a direct link between these experimental measurements and ab initio DFT calculations. Metallocenes such as cobaltocene and methylated ferrocene derivatives were encapsulated inside SWNT (1.4 nm diameter) and the cyclic voltammetry (CV) performed. The electron transfer between guest-molecules and host-SWNT is measured as a function of shift in the redox potential (E1/2) . Furthermore, the shift in E1/2 is shown to be inversely proportional to the nanotube diameter. For the quantification of the amount of electron transfer from the guestmolecules on the SWNT, a novel method using coulometry was developed allowing the mapping of the density of states (DOS) and the Fermi level of the SWNT. Correlated with theoretical calculations, coulometry provides an accurate indication of n/p-doping of the SWNT.

Stereochemistry of Simple Molecules inside Nanotubes and Fullerenes: Unusual Behavior of Usual Systems

“…A general characteristic of all clusters is the decrease in C−C bond length with simultaneous reduction of its Mulliken bond order and appearance of positive or negative electric charge on the guest molecule in accordance with the conclusions of [27,29,[35][36][37]43,52,62,66]. SWCNTs with zig-zag geometry, (6,0)-short and (6,0)-long, differ in length (7.11 and 9.34 Å respectively).…”

“…The structure and properties of hybrid molecule-nanotube and fullerene systems were investigated with both experimental and theoretical methods. In addition to the practical use (such clusters, with unique magnetic and optical properties, are interesting as conductors and semiconductors, effective transporters of drugs in biological systems, and for hydrogen and methane storage) it is important to note that due to the extensive charge transfer between the carbon cage and the guest molecule, the latter acquires an electric charge [27,29,[35][36][37]43,52,62,66]. Besides that, weak and van der Waals interactions play an important role in the molecular encapsulation [66].…”

Host–Guest Hybrid Redox Materials Self‐Assembled from Polyoxometalates and Single‐Walled Carbon Nanotubes

“…Linear sweep voltammetry (LSV) of empty SWNTs shows that low currents flow at voltages corresponding to the energy of the SWNT bandgap, and high currents flow at voltages corresponding to the energies of the van Hove singularities . The Fermi potential of the SWNTs (top level of the highest van Hove singularity in the valence band) is higher than those of the POM lowest unoccupied molecular orbitals (LUMOs) (estimated from solution‐phase voltammetry of the POMs, Figure B,C), explaining the spontaneous electron transfer from the SWNTs to POMs (Figure B) …”

Direct Synthesis of Multiplexed Metal‐Nanowire‐Based Devices by Using Carbon Nanotubes as Vector Templates

“…UV/Vis and photoluminescence spectroscopy analysis of empty and filled SWNTs (see Figures SI‐7 and SI‐8) revealed shifts and quenching, which indicated modification of the electronic states of the filled SWNTs as compared to the empty SWNTs. We propose that upon decomposition of the metal precursors (M 2+ ) to form nanowires (M 0 ), the nature of the guest/nanotube interactions, and consequently the effective density of states of the nanotube, changes, thus resulting in a reduction in the conductivity of the nanotubes . A control experiment was performed using pristine empty SWNTs in devices before and after annealing; in this case the conductivity was observed to increase after annealing, most likely as a result of the improved electrical contact between the nanotube and the gold electrodes (see Figure SI‐9 a) …”