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.

Hironobu Tahara,Yudai Tanaka,Hiroto Murakami,Shigeki Yonemori,Shoko Yamamoto,Takamasa Sagara,Bun Chan

doi:10.1039/d0sc06244h

Abstract

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.

Highlights

Charge transfer (CT) interaction between a donor and acceptor has been of great interest because it can determine the material structures, electric conduction, and photoconduction in solid state.[1]
Chemical structures of the carbazole-based Redox-active ionic liquids (RAILs) ([CzC4ImC1] [TFSI]) and the viologen-based RAIL ([C4VC7][TFSI]2) in this study are shown in Scheme 1, with a photo of the combined CTIL straightforwardly prepared from an equimolar mixture between them
Synthetic procedures of the RAILs, water content in the RAILs, and experimental setups are described in the Electronic supplementary information (ESI).† All measurements in this study were conducted in neat RAILs, namely without any solvent, unless otherwise mentioned. [C4VC7][TFSI]2 remains in a supercooled liquid state for a few hours at room temperature a er it was heated above the melting point (52 C).[46]

Summary

Introduction

Charge transfer (CT) interaction between a donor and acceptor has been of great interest because it can determine the material structures, electric conduction, and photoconduction in solid state.[1]. Because ILs are designer solvents[9] that can be readily created by combining organic cations and anions, one can straightforwardly tune their viscosity, ionic conductivity, and melting point, as well as the solubility of substrate molecules. This leads to some notable advantages over typical organic solvents. ILs are o en preferred due to the higher solubility of solutes such as cellulose[10] and CO2.11,12 they are frequently applied to extraction and separation chemistry.[13] ILs provide interesting functionalities rarely found in organic molecular solvents,[14] leading to unique IL-based liquid materials. Organic cations can be modi ed to further transform ILs into functionalized ionic liquids (FILs) or task-speci c ionic liquids.[15]

Objectives

Results

Conclusion