Series Of Imidazolium Ionic Liquids Research Articles

Bright Free‐Radical Emission in Ionic Liquids

AbstractIt is challenging to achieve stable and efficient radical emissions under ambient conditions. Herein, we present a rational design strategy to protect photoinduced carbonyl free radical emission through electrostatic interaction and spin delocalization effects. The host‐guest system is constructed from tricarbonyl‐substituted benzene molecules and a series of imidazolium ionic liquids as the guest and host, respectively, whereby the carbonyl anion radical emission can be in situ generated under the light irradiation and further stabilized by electrostatic interaction. More importantly, the anion species and the alkyl chain length of imidazolium ionic liquids show a noticeable effect on luminescence efficiency, with the highest radical emission efficiency is as high as 53.3 % after optimizing the imidazole ionic liquid's structure, which is about four times higher than the polymer‐protected radical system. Theoretical calculations confirm the synergistic effect of strong electrostatic interactions and that the spin delocalization effect significantly stabilizes the radical emission. Moreover, such a radical emission system also could be integrated with a fluorescent dye to induce multi‐color or even white light emission with reversible temperature‐responsive characteristics. The radical emission system can also be used to detect different amine compounds on the basis of the emission changes and photoactivation time.

Bright Free-Radical Emission in Ionic Liquids.

It is challenging to achieve stable and efficient radical emissions under ambient conditions. Herein, we present a rational design strategy to protect photoinduced carbonyl free radical emission through electrostatic interaction and spin delocalization effects. The host-guest system is constructed from tricarbonyl-substituted benzene molecules and a series of imidazolium ionic liquids as the guest and host, respectively, whereby the carbonyl anion radical emission can be in situ generated under the light irradiation and further stabilized by electrostatic interaction. More importantly, the anion species and the alkyl chain length of imidazolium ionic liquids show a noticeable effect on luminescence efficiency, with the highest radical emission efficiency is as high as 53.3 % after optimizing the imidazole ionic liquid's structure, which is about four times higher than the polymer-protected radical system. Theoretical calculations confirm the synergistic effect of strong electrostatic interactions and that the spin delocalization effect significantly stabilizes the radical emission. Moreover, such a radical emission system also could be integrated with a fluorescent dye to induce multi-color or even white light emission with reversible temperature-responsive characteristics. The radical emission system can also be used to detect different amine compounds on the basis of the emission changes and photoactivation time.

Probing the impact of alkyl chain length of imidazolium ionic liquids on the conformational stability of collagen type-I from skin of Lutjanus erythropterus

Multispectroscopic techniques and molecular docking study were carried out to inspect the role of concentrations and cationic chain length of ionic liquids (ILs), on the secondary structure of collagen type-I. To attain this objective, a series of imidazolium ILs having same anion (Cl−) and a set of cations with varying chain length were used in this study. The ILs studied utilized are 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), 1-hexyl-3-methylimidazolium chloride ([Hmim][Cl]), and 1-decyl-3-methylimidazolium chloride ([Dmim][Cl]). The effect of these ILs on collagen type-I was analyzed by using UV-vis, circular dichroism (CD), steady state fluorescence, time resolve fluorescence (TRF), synchronous fluorescence, dynamic light scattering (DLS), fourier transform infrared spectroscopy (FT-IR) and molecular docking approach. The results obtained shows the stability of the collagen was dependent on the alkyl chain length of cation as well as concentration of these ILs. The alteration in hydrogen bonding and hydrophobic interactions due to the different cations of ILs, with the amino acid residues, play a key role in unfolding/destabilization of collagen. Consequently, the destabilization propensity of the ILs toward the collagen increases with increasing chain length of ILs. In addition, when organized in the order of providing destability to collagen triple helix structure, the cations of the ILs obeyed the Hofmeister series. Molecular docking also confirms more hydrophobic interaction and reduced hydrogen bonding due to long alkyl chain length of cations in ILs. The docking results are in agreement with the spectroscopic results and provide the information about the ligand binding site on the protein.

Particle size and pore adjustment of dendritic mesoporous silica using different long alkyl-chain imidazolium ionic liquids as templates

The fine-tuning of the pore structure on the mesoscopic scale of dendritic mesoporous silica nanoparticles (DMSNs) is a challenge but very important. In this work, a series of imidazolium ionic liquids (ILs) with different alkyl chain lengths (named CxMImBr: x = 12, 14, 16, 18, 20, and 22, respectively) were synthesized as structure-directing agents based on the highly designable structural advantages of ILs, and the particle size and pore adjustment of DMSNs was investigated. Through the reasonable regulation of alkyl chain length, molar mass, and ratio, it can realize the fine control of monodisperse DMSNs pore size (2–21 nm) and particle size (200–500 nm). On this basis, the pore size and particle size can be further controlled independently by reasonable design of reaction condition. This study provides a controlled way to construct multi-scale and multi-level DMSNs materials.

A study of changes in the heat capacity of carbon nanotube-based ionanofluids prepared from a series of imidazolium ionic liquids.

Ionanofluids (INFs), nanoparticles dispersed into a base fluid, e.g. an ionic liquid, are a novel class of alternative heat transfer fluids. Addition of nanoparticles to a base ionic liquid is the prime reason for an enhancement in the thermophysical properties of ionanofluids. However, due to very limited research on ionanofluids, further studies are required to understand changes in the isobaric heat capacity of ionanofluids as a function of size of cations of the base ionic liquid structure and concentration of nanoparticles. Herein, isobaric heat capacity was measured as a function of temperature for the prepared ionanofluid samples from a series of imidazolium ionic liquids and multi walled carbon nanotubes (MWCNTs). Moreover, the influence of the size of cations on the isobaric heat capacity enhancement mechanism and the stability of ionanofluid samples was studied. Furthermore, experimental isobaric heat capacity data were assessed by a novel non-statistical data analysis method named mathematical gnostics (MG). MG marginal analysis was used to evaluate the most probable values from the measured data set. A robust linear regression along a gnostic influence function was also used to find the best fit to correlate the measured data.

New Functionalized Ionic Liquids Based on POSS for the Detection of Fe3+ Ion.

This study reports a novel series of imidazolium ionic liquids (ILs) based on polyhedral oligomeric silsesquioxanes (POSS) towards effective detection of metal ions, especially Fe3+ ion. 1H, 13C, 29Si NMR, high resolution mass spectra (HRMS) and Fourier transform infrared spectra (FTIR) were applied to confirm the structures of the ILs based on POSS (ILs-POSS). The three ILs-POSS were synthesized via a green chemistry approach—a thiol-ene “click” reaction without metal ions as catalysts. Furthermore, the spherical vesicle structures of the ILs-POSS were observed and caused by self-assembly behaviors. Through comprehensive characterizations, these ILs-POSS have performed excellent thermal stabilities and low glass transition temperatures. In addition, we found it very meaningful that the limits of detection (LODs) of the three ILs-POSS for the detection of the Fe3+ ion were 7.91 × 10−8 M, 1.2 × 10−7 M, and 1.2 × 10−7 M, respectively. These data illustrate that these ILs-POSS have great potential for the detection of the Fe3+ ion. In conclusion, this study not only prepared novel ILs-POSS, but also provided new materials as fluorescent sensors in the detection of Fe3+.

Synergy of imidazolium ionic liquids and flexible anionic polymer for controlling facilely montmorillonite swelling in water

The hydration and swelling of clay minerals in the reservoir will probably bring about serious damage to stratum. Herein, a series of imidazolium ionic liquids (ILs) with different alkyl chains were synthesized to inhibit the swelling of montmorillonite (MMT). The relationship between the inhibitory property and ILs structure was determined through detailed studies. The combination of adsorption capacity, XPS and zeta potential demonstrated that ILs successfully adsorbed on MMT replacing Na+ ion. The adsorption behavior of ILs correlated well with Langmuir adsorption isotherm, implying the homogeneous monolayer adsorption. Besides, the presence of moderate amounts of flexible hydrolyzed polyacrylamide (HPAM) was favorable to improve the inhibition ability of ILs, where HPAM was adsorbed on the surface of MMT through ILs bridging, encapsulating the MMT particles. To understand inhibition mechanism in depth, the interlayer variation of dry and wet MMT and micromorphology of MMT particles were investigated to confirm the intercalation of ILs and stacking variation of MMT particles. Altogether, this study provides new insights into the structure-property relationships of imidazolium ILs and facilitates the design of excellent clay stabilizers.

Insight into the Relationship between Viscosity and Hydrogen Bond of a Series of Imidazolium Ionic Liquids: A Molecular Dynamics and Density Functional Theory Study

The viscosity of ionic liquids (ILs) is an important factor for their industrial applications, which determines mass transfer efficiency. In this work, the relationship between molecular structures and viscosity for three imidazolium-based ILs is investigated by molecular dynamics simulations and density functional theory. The shear viscosity was calculated by using periodic perturbation method, and accurate viscosities are obtained with less than 13% errors as compared to experimental values. Radial distribution functions and space distribution functions reveal that viscosities are correlated strongly to the local structures of ion pairs. Especially, the local aggregation of anions in certain sites of cations prevents movements of the ion pairs, which increase the viscosities of ILs. DFT calculations were further performed to analyze the effects of hydrogen bonds on the viscosities. The results show that asymmetrically distributed interaction sites lead to the high viscosities, which could be used as a rule of thumb for the future design of ILs with target viscosity.

Effect of Hydroxyl Groups in a Cation Structure on the Properties of Ionic Liquids

Two series of imidazolium ionic liquids with the bis(trifluoromethylsulfonyl)imide anion were synthesized, which differ by the presence of a hydroxyl group at the ω-position of the alkyl substituent in the cation structure (nC = 2–8). The properties of the liquids were studied by DSC, TGA, and IR and NMR spectroscopy. Their thermal stability was studied, and the melting points, viscosity, and volatility in vacuum were measured. The effect of OH groups in the structure of the ionic liquid on its properties was evaluated.

Ionic liquid mediated organophilic carbon dots for drug delivery and bioimaging

By taking advantage of the structural tunability of ionic liquids (ILs), a series of imidazolium ILs were employed as precursors to prepare carbon dots (IL-CDs) and as regulators to control their properties. The simultaneous formation of hydrophilic CDs (IL-HCDs) and organophilic CDs (IL-OCDs) is achieved in hydrothermal reaction system by undergoing sulfuric acid carbonization. The quantum yields (QY) of IL-OCDs are closely correlated with both the cationic and anionic moieties of the ionic liquids, i.e., longer side chains of cations in the imidazolium ILs and weakly nucleophilic anions tend to produce highly fluorescent IL-OCDs. Both IL-HCDs and IL-OCDs exhibit low cytotoxicity, and that of IL-HCDs is even lower than IL-OCDs. A drug delivery system is constructed by combining anticancer drug curcumin (Cur) with IL-OCDs via hydrophobic interaction, among which 1,3-dibutylimidazolium nitrate derived IL-OCDs exhibit highest photoluminescence. In addition, it serves as a favorable drug carrier with high drug loading efficiency and facilitates rapid penetration/transportation of Cur into the cell interior, which significantly accelerates the apoptosis of HeLa cells. This process is further visualized by cell imaging.

Phenolic hydroxyl-functionalized imidazolium ionic liquids: Highly efficient catalysts for the fixation of CO2 to cyclic carbonates

A series of imidazolium ionic liquids were designed and synthesized by the reaction of imidazole derivatives with alkyl bromides. These ionic liquids were applied to catalyze the reaction of CO2 and epoxides. A detailed investigation was carried out on the relationship between catalytic activities and catalyst structures. The result showed that phenolic hydroxyl-functionalized imidazolium ionic liquids containing both phenolic hydroxyl and C2-H were highly efficient catalysts. Meanwhile, the spatial positions of the phenolic hydroxyl and C2-H in the imidazolium also exhibited great effect on the catalytic efficiencies, and the order of catalytic activity was meta-isomer>ortho-isomer>para-isomer. NMR titration and DFT calculations showed a synergetic effect, which C2-H and phenolic hydroxyl cooperatively activated epoxides by hydrogen bonds, was crucial for the reaction to proceed smoothly under mild conditions. In addition, the TOF of the most active catalyst 3-(3-phenolic hydroxyl)-1-butyl-imidazolium bromide (IL-2) reached to 900h−1 in the reaction of CO2 and epichlorohydrin under the reaction conditions of 0.1mol% catalyst, 1MPa CO2, 120°C and 1h.

Role of Solvent and Effect of Substituent on Azobenzene Isomerization by Using Room-Temperature Ionic Liquids as Reaction Media.

The effects of a para substituent, as the electron-donating -OCH3 and -OtBu groups and the electron-withdrawing -Br and -F atoms, on azobenzene isomerization have been investigated in a series of imidazolium ionic liquids (BMIM PF6, BMIM BF4, BMIM Tf2N, EMIM Tf2N, BM2IM Tf2N, and HMIM Tf2N). The thermal cis-trans conversion tends to be improved in the presence of the substituent, as pointed out by the first-order rate constants measured at 25 °C. Both the rotation and the inversion mechanisms occur in BMIM Tf2N, EMIM Tf2N, and HMIM Tf2N, as highlighted by typical V-shape Hammett plots, but only rotation takes place in BMIM PF6, BMIM BF4, and BM2IM Tf2N. The possible interactions between the cation and the anion of the solvent and both the isomers of the azobenzene derivatives have been studied by small-wide-angle X-ray scattering (SWAXS). The calculated cis population in the photostationary state and the hardness parameter η of the trans isomer show that azobenzene and F-azobenzene are the less reactive molecules for the trans-cis conversion in all the investigated ionic liquids.

Impact of Electrode Nature on Lithium-Ion Battery Performances with Ionic Liquids or Carbonate Electrolytes

Lithium-ion batteries have rapidly become the most common power source for portable electronic devices, power tools and electric vehicles due to their high energy density and good cycling stability. However, before implementation of the Li-ion batteries in EVs and HEVs, many features still must be resolved, like low cost, long calendar life, safety and high power capability (1). Replacement of the organic carbonates with more thermally and electrochemically stable ionic liquids (ILs) could increase the security (2). A lot of work was already reported in the literature about the ILs as electrolytes, especially in comparison of cycling with organic electrolyte, but still with different electrodes combination. By following the nature of the electrodes couples, the power capacity could be tuned (1). Nevertheless, a few systematic comparison of these different systems are available (3-4). In this work, we report the performance of three full cell configurations: graphite (Cgr)// LiFePO4 (LFP), Li4Ti5O12 (LTO)// LiFePO4 (LFP) and Li4Ti5O12 (LTO)// LiNi1/3Mn1/3Co1/3O2 (NMC), with five different ionic liquids and one organic carbonate electrolytes. Their cycling results, at 333 K, with a pyrrolidinium [PYR14][NTf2], series of imidazolium ionic liquids ([C1CnIm][NTf2] and [C1C1CnIm][NTf2]/ n= 4 and 6) associated with LiNTf2 (1mol.L-1) then an organic electrolyte (LiPF6 (1mol.L-1) DEC: EC), are depicted in Figure 1 (a-c). Some trends have been found. For Cgr//LFP system cycling is observed only in the presence of organic additive, vinylene carbonate (VC) (Fig. 1a). Carbonates, except for LTO//NMC cell, show lower capacity then ILs based electrolytes (Fig. 1). The highest capacity is observed for LTO//NMC system with ([C1C4Im][NTf2], [PYR14][NTf2] and carbonate electrolyte, ~180 mAh.g-1, ~140 mAh.g-1 and ~180 mAh.g-1, respectively (Fig. 1c). The introduction of a donating group (-CH3) on position two of the imidazolium ring (C2-H → C2-CH3) in [C1C1CnIm][NTf2] highly improve the performance of Cgr//LFP cells (Fig. 1) (5). Besides LTO//NMC, the charge/discharge performance is improved by extending the alkyl chain length of the imidazolium ring. Finally, in LTO//LFP and LTO//NMC, higher performances were obtained with ([C1C4Im][NTf2] compare to [PYR14][NTf2]. From these results, we highlight the tremendous impact of each element of the system (electrode, electrolyte, and separator (6)) onto the charge discharge capacity, especially with ionic liquids based ones.

Tribological and corrosive properties of ionic liquids containing triazole functional groups

Purpose – The aim of this paper was to inhibit the serious corrosion of conventional ionic liquids, a series of new ionic liquids (ILs) containing the triazole functionality, as the anti-corrosion groups were synthesized in this work. Design/methodology/approach – It is well known that nitrogen and sulfur containing organic compounds have been traditionally used as corrosion inhibitors. Among them, triazole derivatives are most often used as corrosion inhibitors. To alleviate the corrosion of the ILs and further improve the anti-wear property, the authors prepared a series of imidazolium ILs modified with the triazole functionality in the present study. Findings – The corrosion behavior of the ILs was evaluated with the iron disk corrosion test and their tribological properties were investigated on an Optimol SRV IV oscillating friction and wear tester at elevated temperatures. The results showed that the ILs with the triazole functionality could effectively reduce the corrosion and exhibit a smaller friction coefficient and wear volume than the unmodified counterpart. The ILs containing the triazole functionality can be used as the single component anti-corrosion base oils even at elevated temperatures. Originality/value – The results showed that the ILs with the triazole functionality could effectively reduce the corrosion and exhibit a smaller friction coefficient and wear volume than the unmodified counterpart. The ILs containing the triazole functionality can be used as the single component anti-corrosion base oils even at elevated temperatures.

Ultrafast Solvation Dynamics in Room Temperature Ionic Liquids Observed by Three-Pulse Photon Echo Peak Shift Measurements

Three-pulse photon echo peak shift (3PEPS) measurement was applied to the investigation of the primary part (<100 ps) of the solvation dynamics in a series of imidazolium ionic liquids (IL) with an organic dye, oxazine 4 (Ox4), utilized as a probe. The ultrafast solvent response in the range of ≤300 fs exhibited dependence on the square root of the anion mass, indicating its relation with the inertial motion of anion. The inertial response of ILs with chloride anion was the fastest among other ILs with heavier and larger anions. Because Ox4 is a cationic dye, it holds a stronger interaction with the anion of IL, thus the ultrafast part of the solvation is strongly affected by the inertial motion of anions. The second solvation component in the range of ≤3.5 ps had better correlation with the reduced mass and the size of both ions included, indicating the beginning of a more global solvation process.

이온성 액체에 의한 CdSe/ZnS 나노입자의 상과 크기제어 합성

이온성 액체는 일정한 온도 범위에서 액체로 존재하는 이온성 염으로, 유기 양이온과 유기 또는 무기 음이온의 이온결합으로 이루어져 있다. 본 연구에서는 이온성 액체를 CdSe/ZnS 반도체 나노입자 합성의 리간드 및 용매로 사용하여 이들이 나노입자의 형태와 결정 구조에 미치는 영향에 대해서 연구하였다. CdSe/ZnS 나노입자는 용매로 알킬기의 길이가 다른 imidazolium 계열; 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([RMIM][TFSI]), R = ethyl ([EMIM]), butyl ([BMIM]), hexyl ([HMIM]), octyl ([OMIM]), 을 사용하여, 평균 크기는 약 8~9 nm 이고 두 상 zinc-blende 및 wurtzite 혼합물로 합성하는 것을 성공하였다. 또한, CdSe/ZnS 나노입자는 trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([<TEX>$P_{6,6,6,14}$</TEX>][TFSI]) 이온성 액체와 octadecene (ODE)의 혼합 용액을 사용하여 합성하였다. [<TEX>$P_{6,6,6,14}$</TEX>][TFSI]의 부피비가 증가함에 따라 나노입자의 결정 구조가 zinc-blende 구조에서 wurtzite 구조로 조절되었다. 또한 나노입자의 평균 크기는 약 5.5 nm 로써 [RMIM][TFSI] 를 사용했을 때 보다 더 작게 합성되었다. 이처럼 이온성 액체에 의해서 나노입자의 크기뿐 만 아니라 결정 구조도 조절할 수 있음을 처음으로 증명하였다. Ionic liquids are room-temperature molten salts, composed of organic mostly of organic ions that may undergo almost unlimited structural variation. We approach the new aspects of ionic liquids in applications where the semiconductor nanoparticles used as sensitizers of solar cells. We studied the effects of ionic liquids as capping ligand and/or solvent, on the morphology and phase of the CdSe/ZnS nanoparticles. Colloidal CdSe/ZnS nanoparticles were synthesized using a series of imidazolium ionic liquids; 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([RMIM][TFSI]), where R = ethyl ([EMIM]), butyl ([BMIM]), hexyl ([HMIM]), octyl ([OMIM]). The average size of nanoparticles was 8~9 nm, and both zinc-blende and wurtzite phase was produced. We also synthesized the nanoparticles using a mixture of trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([<TEX>$P_{6,6,6,14}$</TEX>][TFSI]) and octadecene (ODE). The CdSe/ZnS nanoparticles have a smaller size (5.5 nm) than that synthesized using imidazolium, and with a controlled phase from zinc-blende to wurtzite by increasing the volume ratio of [<TEX>$P_{6,6,6,14}$</TEX>][TFSI]. For the first time, the phase and size control of the CdSe/ZnS nanoparticles was successfully demonstrated using those ionic liquids.

Biodegradable, non-bactericidal oxygen-functionalised imidazolium esters: A step towards ‘greener’ ionic liquids

A series of imidazolium ionic liquids was prepared and screened against 7 bacterial strains. The incorporation of ether groups into the ester side-chain significantly reduced the toxicity compared with alkyl ester derivatives. Biodegradation data are also presented for 15 of the ionic liquids—including 6 examples which can be classed as readily biodegradable.