Switchable ionic conductivity and viscoelasticity of ionogels containing photo- and thermo-responsive organometallic ionic liquids

Deep eutectic solvent-based ionogel: Innovative potential as a promising chromatographic separation material

BACKGROUND

Ionogels, composed of cross-linked polymer networks with abundant anions and cations as dispersion media, have emerged as promising materials. The superior properties of ionogels suggest that they may offer valuable contributions to the development of novel chromatographic stationary phase. However, the potential application of ionogels as the charming materials in liquid chromatography has been limited, primarily due to the hydrophilic nature, leading to swelling and increased column pressure. To address this issue, a paradigm-shifting innovation was proposed by incorporating deep eutectic solvent (DES) to facilitate the formation of robust hydrogen bond networks, thereby reducing the swelling tendency of ionogel.

RESULTS

In this study, an environmentally friendly DES was selected as the optimal alternative to the traditional ionic liquid for the formation of a DES-based ionogel. By combining the ionogel with the silica gel matrix, a DES-Ionogel@SiO2 stationary phase was prepared. The whole synthesis process of DES-Ionogel@SiO2 was conducted in the green DES. The swelling tendency of ionogel as a functionalized chromatographic material was significantly reduced, thereby mitigating the risk of undue column pressure. This innovation results in a DES-based stationary phase with enhanced stability and durability in aqueous media, which is pivotal for maintaining the performance and longevity of chromatographic column. The DES-Ionogel@SiO2 stationary phase exhibits a distinctive mixed-mode retention mechanism, which is a highly desirable attribute in diverse chromatographic applications. This endows the developed chromatographic column with a broad applicability for the separation of complex samples, such as nucleosides, phenyl ketones, phthalates, alkylphenols, steroid hormones and position isomers.

SIGNIFICANCE

This work presents an innovative approach and green in-situ growth strategy for the development of a versatile ionogel stationary phase, and marks the first time that DES-based ionogel has been synthesized and used to modify silica gel as a promising chromatographic separation material, showcasing the revolutionary potential of DES-based ionogel in the field of liquid chromatography.

Modulating the Conductivity of Light-Responsive Ionic Liquid Crystals

In this work, we describe the phase behaviour and the dielectric and conductivity response of new light-responsive ionic liquid crystals, ILCs, which can be applied as controllable electrolytes. The materials include two different dicationic viologens, the asymmetric 6BP18 and the symmetric EV2ON(Tf)2, containing bistriflimide as the counterions, mixed with 5% and 50% molar, respectively, of one new photoresponsive mesogen called CNAzO14. These mixtures exhibit liquid crystal behaviour, light responsiveness through the E-Z photoisomerisation of the azobenzene groups in CNAzO14, and strong dielectric responses. The 5%-CNAzO14/Ev2ON(Tf)2 mixture displays direct current conductivities in the 10-7 S·cm-1 range, which can be increased by a two-fold factor upon the irradiation of UV light at 365 nm. Our findings set the grounds for designing new smart ionic soft materials with nanostructures that can be tuned and used for energy conversion and storage applications.

Thiol-ene chemistry incorporates a new spiropyran-containing polyurethane ionogel with photochromic, photomechanical and photoconductive properties

The photocuring technology based on thiol-ene click reaction can be easily applied for copolymerizing or crosslinking the acrylate monomers for ionogels. However, there is still a problem: when the acrylate monomers contain the popular spiropyran as the stimuli-responsive group, it should be concerned about the participation of the active CC bond from the ring-opened spiropyran during a thiol-ene reaction, which may in turn affect the stimuli-responsiveness of the spiropyran. Up to now, the structure and properties of spiropyran-containing ionogels in this case have still not been well investigated. Therefore, in this work we carefully study a new spiropyran-containing polyurethane ionogel by crosslinking an acrylate-terminated, spiropyran-containing polyurethane prepolymer and a polythiol in ionic liquid through thiol-ene chemistry. It is found for the first time that, during constructing an ionogel, the coexistence of a reversible thiol-ene reaction between the CC bond from the ring-opened spiropyran and the thiol group can bring about a different reverse photochromic behavior. The proposed mechanism of the abnormal photochromism is analyzed. In addition, it is also observed that the thiol-ene chemistry can incorporate photomechanical and photoconductive properties into the new spiropyran-containing ionogel.

Organometallic Ionic Liquids Containing Sandwich Complexes: Molecular Design, Physical Properties, and Chemical Reactivities

Ionic liquids (ILs) are salts with low melting points and are useful as electrolytes and solvents. We have developed ILs containing cationic metal complexes, which form a family of functional liquids that exhibit unique physical properties and chemical reactivities originating from metal complexes. Our study explores the liquid chemistry in the field of coordination chemistry, where solid-state chemistry is currently the main focus. This review describes the molecular design, physical properties, and reactivities of organometallic ILs containing sandwich or half-sandwich complexes. This paper mainly covers stimuli-responsive ILs, whose magnetic properties, solvent polarities, colors, or structures change by the application of external fields, such as light, heat, and magnetic fields, or by reaction with coordinating molecules.