Thioimidazolium Ionic Liquids as Tunable Alkylating Agents

Alkylating ionic liquids based on the thioimidazolium structure combine the conventional properties of ionic liquids, including low melting point and nonvolatility, with the alkylating function. Alkyl transfer occurs exclusively from the <i>S</i>-alkyl position, thus allowing for easy derivatization of the structure without compromising specificity. We apply this feature to tune the electrophilicty of the cation to profoundly affect the reactivity of these alkylating ionic liquids, with a caffeine-derived compound possessing the highest reactivity. Anion choice was found to affect reaction rates, with iodide anions assisting in the alkylation reaction through a “shuttling” process. The ability to tune the properties of the alkylating agent using the toolbox of ionic liquid chemistry highlights the modular nature of these compounds as a platform for alkylating agent design and integration in to future systems

Anion-Exchange Reactions on a Robust Phosphonium Photopolymer for the Controlled Deposition of Ionic Gold Nanoclusters

UV curing (photopolymerization) is ubiquitous in many facets of industry ranging from the application of paints, pigments, and barrier coatings all the way to fiber optic cable production. To date no reports have focused on polymerizable phosphonium salts under UV irradiation, and despite this dearth of examples, they potentially offer numerous substantial advantages to traditional UV formulation components. We have generated a highly novel coating based on UV-curable trialkylacryloylphosphonium salts that allow for the fast (seconds) and straightforward preparation of ion-exchange surfaces amenable to a roll-to-roll process. We have quantified the surface charges and exploited their accessibility by employing these surfaces in an anion exchange experiment by which [Au₂₅L₁₈]⁻ (<i>L</i> = SCH₂CH₂Ph) nanocrystals can be assembled into the solid state. This unprecedented application of such surfaces offers a paradigm shift in the emerging chemistry of Au₂₅ research where the nanocrystals remain single and intact and where the integrity of the cluster and its solution photophysical properties are resilient in the solid state. The specific loading of [Au₂₅L₁₈]⁻ on the substrates has been determined and the completely reversible loading and unloading of intact nanocrystals to and from the surface has been established. In the solid state, the assembly has an incredible mechanical resiliency, where the surface remains undamaged even when subjected to repeated Scotch tests

Trends in Hydrophilicity/Lipophilicity of Phosphonium Ionic Liquids As Determined by Ion-Transfer Electrochemistry

Ionic liquids (ILs) have become valuable new materials for a broad spectrum of applications including additives or components for new hydrophobic/hydrophilic polymer coatings. However, fundamental information surrounding IL molecular properties is still lacking. With this in mind, the microinterface between two immiscible electrolytic solutions (micro-ITIES), for example, water|1,2-dichloroethane, has been used to evaluate the hydrophobicity/lipophilicity of 10 alkylphosphonium ILs. By varying the architecture around the phosphonium core, chemical differences were induced, changing the lipophilicity/hydrophilicity of the cations. Ion transfer (IT) within the polarizable potential window (PPW) was measured to establish a structure–property relationship. The Gibbs free energy of IT and the solubility of their ILs were also calculated. For phosphonium cations bearing either three butyl or three hydroxypropyl groups with a tunable fourth arm, the latter displayed a wide variety of easily characterizable IT potentials. The tributylphosphonium ILs, however, were too hydrophobic to undergo IT within the PPW. Utilizing a micro-ITIES (25 μm diameter) housed at the tip of a capillary in a uniquely designed pipet holder, we were able to probe beyond the traditional potential window and observe ion transfer of these hydrophobic phosphonium ILs for the first time. A similar trend in lipophilicity was determined between the two subsets of ILs by means of derived solubility product constants. The above results serve as evidence of the validation of this technique for the evaluation of hydrophobic cations that appear beyond the conventional PPW and of the lipophilicity of their ILs

Linear and Cross-Linked Ionic Liquid Polymers as Binders in Lithium–Sulfur Batteries

A collection of different polymeric ionic liquids (PILs) were explored as cathode binders in lithium–sulfur batteries. The PIL molecular structure, polymer backbone, and polymer architecture were found to influence the cell capacity, the cyclability, and the morphology of the cathode itself. PILs with styrene backbones performed better than the vinyl-based polymer, while cross-linked PILs imparted further improved capacities, cyclability, and reduced overpotentials. Unlike polyvinylidene fluoride, PIL binders mixed with the sulfide species, resulting in more uniformly distributed sulfides in the cathode and better sulfide transport. These features helped to mitigate volume change-induced degradation that typically plagues Li–S batteries. The uptake of polysulfides by PILs also constrains the polysulfide shuttle during battery cycling, leading to better cycling stability. While traditionally binders are viewed only as a “glue” to hold the active material together, PIL binders have additional functions and play an active role during Li–S battery working operation

Patterned Phosphonium-Functionalized Photopolymer Networks as Ceramic Precursors

In an attempt to address the growing demand for well-defined metallized regions for electronic applications, we developed a new method of forming patterned ceramics. Using UV-curing to synthesize a phosphonium-containing semi-interpenetrating polymer network (S-IPN) followed by ion exchange on the surface with a bis­(phosphino)­borate molybdenum tetracarbonyl complex (2Mo) results in 71% ion exchange of 2Mo to phosphonium sites by attenuated total reflectance infrared (ATR-IR) spectroscopy. The functionalized films were pyrolyzed at temperatures ranging between 800 and 1000 °C to create Mo-containing ceramics. The polymer network can be patterned using electron beam lithography prior to the metal functionalization step. The patterns had good shape retention after metal functionalization and pyrolysis. The polymer networks were characterized using ATR-IR spectroscopy, thermogravimetric analysis, and differential scanning calorimetry, and the swellability and gel content were determined. The resulting ceramics were characterized using optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction

Flexible and Actuating Nanoporous Poly(Ionic Liquid)–Paper-Based Hybrid Membranes

Porous and flexible actuating materials are important for the development of smart systems. We report here a facile method to prepare scalable, flexible actuating porous membranes based on a poly­(ionic liquid)-modified tissue paper. The targeted membrane property profile was based on synergy of the gradient porous structure of a poly­(ionic liquid) network and flexibility of a tissue paper. The gradient porous structure was built through an ammonia-triggered electrostatic complexation of a poly­(ionic liquid) with poly­(acrylic acid), which were previously impregnated inside the tissue paper. As a result, these porous membranes undergo deformation by bending in response to organic solvents in the vapor or liquid phase and can recover their shape in air, which demonstrates their ability to serve as solvent sensors. Besides, they show enhanced mechanical properties due to the introduction of mechanically flexible tissue paper that allows the membranes to be designed as new responsive textiles and contractile actuators