Electron transfer controlled by solvent and counter-anion dynamics in electrochemistry of viologen-type ionic liquid

Tuning Photoinduced Electron Transfer in POM-Bodipy Hybrids by Controlling the Environment: Experiment and Theory

The optical and electrochemical properties of a series of polyoxometalate (POM) oxoclusters decorated with two bodipy (boron-dipyrromethene) light-harvesting units were examined. Evaluated here in this polyanionic donor-acceptor system is the effect of the solvent and associated counterions on the intramolecular photoinduced electron transfer. The results show that both solvents and counterions have a major impact upon the energy of the charge-transfer state by modifying the solvation shell around the POMs. This modification leads to a significantly shorter charge separation time in the case of smaller counterion and slower charge recombination in a less polar solvent. These results were rationalized in terms of Marcus theory and show that solvent and counterion both affect the driving force for photoinduced electron transfer and the reorganization energy. This was corroborated with theoretical investigations combining DFT and molecular dynamics simulations.

A redox-active ionic liquid manifesting charge-transfer interaction between a viologen and carbazole and its effect on the viscosity, ionic conductivity, and redox process of the viologen

Redox-active ionic liquids (RAILs) are gaining attention as a material that can create a wide range of functions. We herein propose a charge-transfer (CT) RAIL by mixing two RAILs, specifically a carbazole-based ionic liquid ([CzC₄ImC₁][TFSI]) as a donor and a viologen-based ionic liquid ([C₄VC₇][TFSI]₂) as an acceptor. We investigated the effect of CT interaction on the physicochemical properties of the CT ionic liquid (CT-IL) using the results of temperature-dependent measurements of UV-vis absorption, viscosity, and ionic conductivity as well as cyclic voltammograms. We employed the Walden analysis and the Grunberg–Nissan model to elucidate the effect of the CT interaction on the viscosity and ionic conductivity. The CT interaction reduces the viscosity by reducing the electrostatic attraction between the dicationic viologen and TFSI anion. It also reduces the ionic conductivity by the CT association of the dicationic viologen and carbazole. The electrochemically reversible responses of the viologens in [C₄VC₇][TFSI]₂ and CT-IL are consistent with the Nernstian and the interacting two-redox site models. Notably, the transport and electrochemical properties are modulated by CT interaction, leading to unique features that are not present in individual component ILs. The inclusion of CT interaction in RAILs thus provides a powerful means to expand the scope of functionalized ionic liquids.

A redox-active ionic liquid (RAIL) consisting of a carbazole and viologen shows charge transfer (CT) interaction. The physicochemical properties are modulated by the CT interaction by comparison with the individual RAILs.

Rapid assessment of platinum disk ultramicroelectrodes' sealing quality by a cyclic voltammetry approach

Here, we investigated the sealing quality between a microwire disk and the surrounding glass sheath of platinum disk ultramicroelectrodes (UMEs) using outer-sphere (ferrocene methanol, FcMeOH, oxidation) and inner-sphere electrochemical reactions (hydrogen underpotential deposition (HUPD) and the hydrogen evolution reaction (HER)) by the cyclic voltammetry (CV) approach. The tilt aspect in the CV curves is ascribed to the leakage of the electrolyte solution between the microelectrode wire and the glass sheath, causing an iR drop which shows the resistive nature of CV. The resistive nature of CV was analyzed by performing the HER using both poorly and well-sealed disk UMEs. Scan rate dependent double-layer capacitance (Cdl) data confirm the leak between a glass-wire interface in the UMEs. Further, we showed a quantitative treatment for the sealing assessment using analytical expressions. Overall, we demonstrate a rapid check procedure of the sealing quality in fabricating Pt disk UMEs. The simple procedure presented in this work can be used to evaluate the sealing quality of other types of micro/nanoelectrodes during their fabrication.

Observing Host-Guest Interactions at Molecular Interfaces by Monitoring the Electrochemical Current

Macrocyclic cucurbit[n]uril (CB[n]) molecules have triggered renewed interest because of their outstanding capabilities as host molecules to selectively interact with a wide range of small guest molecules. Here, CB[7]-based host-guest interactions were investigated for a guest-modified nanoelectrode by monitoring the electrochemical current. A ferrocene (Fc)-terminated molecule immobilized on a gold nanoelectrode (GNE) showed suitable affinity with CB[7] when the effective exposing area of the GNE was between 5.3 and 12 μm² and the bias applied on the GNE was -500 mV. Monitoring the dynamics of nanoparticles (NPs) on a nanoelectrode provides new insights into the host-guest interactions at molecular interfaces.