Solvent Effect on Redox Properties of Hexanethiolate Monolayer-Protected Gold Nanoclusters

Abstract

The capacitance of monolayer-protected gold nanoclusters (MPCs), C MPC , in solution has been theoretically reconsidered from an electrostatic viewpoint, in which an MPC is considered as an isolated charged sphere within two dielectric layers, the intrinsic coating monolayer, and the bulk solvent. The model predicts that the bulk solvent provides an important contribution to C MPC and influences the redox properties of MPCs. This theoretical prediction is then examined experimentally by comparing the redox properties of MPCs in four organic solvents: 1,2-dichloroethane (DCE), dichloromethane (DCM), chlorobenzene (CB), and toluene (TOL), in all of which MPCs have excellent solubility. Furthermore, this set of organic solvents features a dielectric constant in a range from 10.37 (DCE) to 2.38 (TOL), which is wide enough to probe the solvent effect. In these organic solvents, tetrahexylammonium bis(trifluoromethylsulfonyl)imide (THATf 2 N) is used as the supporting electrolyte. Cyclic and differential pulse voltammetric results provide concrete evidence that, despite the monolayer protection, the solvent plays a significant effect on the properties of MPCs in solution.

Determination of the optical band gap of Alq3 and its derivatives for the use in two-layer OLEDs

“…The value obtained from CV measurements is $0.1 eV lower in the case of DCM and $0.2 eV lower in the case of CH 3 CN. The values will differ from the theoretical value of Alq 3 because the band gap was determined by a technique were the samples are dissolved and it is known that solvents play a role on the values of the band gap [12]. The substituents do not have a big influence on the band gap and it does not vary more than $0.3 eV from the theoretical value of Alq 3 .…”

Charging and discharging at the nanoscale: Fermi level equilibration of metallic nanoparticles

“…To keep here a simple electrostatic model considering the solvent as a dielectric continuum, the capacitance of an MPC is given by: 17 this equation is self-consistent with eqn (8) when calculating the separation of the redox potentials upon charging. This model can be extended to take into account the effects of the diffuse electrical double layer surrounding the MPC (by both linearized and non-linear Poisson–Boltzmann (P–B) models), 18–20 and also the solvent and ion penetration into the surrounding monolayer.…”

“…This model can be extended to take into account the effects of the diffuse electrical double layer surrounding the MPC (by both linearized and non-linear Poisson–Boltzmann (P–B) models), 18–20 and also the solvent and ion penetration into the surrounding monolayer. 21,22 In fact, the capacitance of an MPC can be considered as two capacitors in series, one for the monolayer of thickness d and one for the bulk solution.with C d = 4π ε 0 ε d ε r r ( r + d )/ d C bulk = 4π ε 0 ε r ( r + d )If we consider the ionic atmosphere around the NP, the bulk capacitance becomes 17 C bulk = 4π ε 0 ε r ( r + d )[1 + κ ( r + d )]with κ the Debye length, determined by the ionic strength of the electrolyte solutions and the relative permittivity of the solvent. These simple equations illustrate the dominating effect of the monolayer when determining the values of the capacitance and, hence, the separation between the different redox potentials.…”

“…17 The most sophisticated approach involves a generalized P–B equation that considers the monolayer as a disordered medium where the thermal motion of the counter ions is decreased because of electrostatic correlations and monolayer structural effects. This generalised P–B equation was proposed on the basis of replacing the Boltzmann distribution by the Tsallis q -exponential distribution.…”

Insights into the Interface Between the Electrolytic Solution and the Gold Core in Molecular Au25 Clusters

“…Au 144 (SR) 60 .T he separation between consecutive peaks (DE) and, thus, the charging energyd epend on the solvent, [34,35] the electrolyte and its concentration, [34,36] the monolayert hickness, [37] and the specific ligand. [27] These QDL MPCs have been described as concentric nanocapacitors characterizedb yv ery small capacitance values, [1,38] with values of 6t o7 10 À19 F. [28,29,34,38,39] The MPC capacitance (C MPC )i se xperimentally estimated from the (average) DE value with the relationship C MPC = e/DE, [38] where e is the charge of the electron.…”