Size Matters! On the Way to Ionic Liquid Systems without Ion Pairing

Rupp, Alexander; Roznyatovskaya, Nataliya; Scherer, Harald; Beichel, Witali; Klose, Petra; Sturm, Carola; Hoffmann, Anke; Tübke, Jens; Koslowski, Thorsten; Krossing, Ingo

doi:10.1002/chem.201400168

Cited by 48 publications

(90 citation statements)

References 64 publications

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“…It is also worth to point out that beyond this ''layering'' of the different ions, the anion and cation have other microscopic properties that show clear differences. For example, it has been shown that the cations have larger mobilities in ILs compared to the anions [28,29], even if the latter particle is significantly smaller in size [30].…”

Section: Resultsmentioning

confidence: 99%

En route formation of ion pairs at the ionic liquid–vacuum interface

et al. 2015

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An increasing lack of single ion cation-anion associations (ion pairing) in ionic liquids suggests a structural motif that stands in contradiction to the single ion pair structure of their vapor phase, which was evidenced by different experimental and theoretical studies. Therefore, a structural rearrangement has to occur en route from the liquid to the vapor. In this study, we propose a detailed four-step evaporation mechanism for ionic liquids, providing a refined perspective on the theory of this process based on the connection between ion pairing and volatility. The process involves diffusion of ions from the bulk to the surface, where they float around until a well-defined ion pair is formed with a counterion, leading to the departure from the surface into the vacuum. To assess the validity of this scheme, we performed a series of classical and ab initio molecular dynamics simulations based on the most sophisticated methods and force fields available for ionic liquids.

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Section: Resultsmentioning

confidence: 99%

En route formation of ion pairs at the ionic liquid–vacuum interface

et al. 2015

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“…30 Consequently, this observation leads to the conclusion that ion-pairing clearly is less favored in [Al(Ohfip) 4 ] − ILs than in [NTf 2 ] − ILs.…”

Section: Self-diffusion Constants and Ion-pairingmentioning

confidence: 84%

“…3 Again, [Al(Ohfip) 4 ] − ILs prove to be the best subclass with conductivities of up to 4 mS·cm −1 at 25°C. 3,30 As with the viscosities, the effect of exchanging cations is relatively negligible compared with [NTf 2 ] − ILs. 30 Imidazolium-based ILs show superior properties compared with ammonium ILs.…”

Section: Accounts Of Chemical Researchmentioning

confidence: 98%

“…In contrast to [Al(Ohfip) 4 ] − , [NTf 2 ] − still has Lewis-basic surface atoms (N, O) and a considerably smaller diameter, leading to stronger and more individual interionic interaction and causing not only the mentioned cation dependence of viscosity but also higher activation barriers for ion movement processes (Figure 4). 30 Another consequence is that viscosities of [Al(Ohfip) 4 4 ]·2.76DMC only produced a roughly 3.5-fold increase in conductivity. Furthermore, the order in conductivity was partially reversed in the case of diffusion constants.…”

Section: Accounts Of Chemical Researchmentioning

confidence: 98%

“…40 A comparative study of diffusion constants of 12 [Al(Ohfip) 4 ] − ILs and their [NTf 2 ] − analogues yielded the ion-specific diffusion constants given in Table 2. 30 From first principles, one would probably assume that [NTf 2 ] − ILs should show larger diffusion constants due to their smaller molecular volume and lower molar mass. However, a more complex picture arises from the diffusion data.…”

Section: Self-diffusion Constants and Ion-pairingmentioning

confidence: 99%

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Ionic Liquids with Weakly Coordinating [M^III(OR^F)₄]⁻ Anions

Rupp

Krossing

2015

Acc. Chem. Res.

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Ionic liquids (ILs) are defined as salts with melting points below 100 °C. They attracted much attention in the last two decades due to their unique set of properties, including high conductivities, low viscosities, negligible vapor pressure, and high electrochemical resistance. ILs are seen as tunable systems, of which (also in mixtures) up to 10(19) combinations may exist. These properties make ILs interesting candidates for a variety of fundamental to industrial applications. Our addition to this field was weakly coordinating, little interacting anions, the highly fluorinated aluminates [Al(OR(F))4](-) (R(F) = C(CF3)3, C(CH3), (CF3)2, and CH(CF3)2 and later also CH2(CF3)). We have used these anions in a broad spectrum of applications, including the stabilization of reactive cations, (polymerization) catalysis, and conducting salts for cyclic voltammetry or in electrochemical cells. Especially the [Al(Ohfip)4](-) (hfip = CH(CF3)2) anions in combination with asymmetric organic cations turned out to be very well suited for the synthesis of ILs with very low melting points, some even far below 0 °C. Also the analogous borates, [B(OR(F))4](-), were shown to yield ILs, and currently a plethora of such aluminate and borate ILs have been synthesized and thoroughly investigated. In many aspects, at least the [Al(Ohfip)4](-) ILs present almost ideally noninteracting prototype ILs with (nearly) isotropic but weak and flat Coulomb potential. Consequently, their overall interionic interactions are significantly reduced compared with other classes of ILs, resulting in an extraordinarily low degree, or (for short cation chain lengths below six) even complete absence of ion pairing. From thorough analysis of the principles governing the physical properties of this highly fluorinated IL class with minimized interactions, we were able to learn basic principles that could be extended, for example, to the prediction of the principal properties of a wide variety of typical ILs. In this Account, we give a comprehensive review of their syntheses, thermal and toxicological behavior, physical as well as dynamic properties, and use in electrochemical applications. We delineate advantages and limitations of the [M(III)(OR(F))4](-) ILs developed in our lab and give an outlook on those fields, in which there is still a lack of knowledge.

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Giant Light‐Harvesting in Dye‐Loaded Nanoparticles Enhanced by Blank Hydrophobic Salts

Biswas,

Melnychuk,

Severi

et al. 2023

Advanced Optical Materials

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Light‐harvesting is a fundamental process in nature, which inspires researchers to develop artificial systems for photocatalysis, photovoltaics, and biosensing. A previously introduced light‐harvesting nanoantenna, based on polymeric nanoparticles (NPs) loaded with rhodamine dyes and bulky hydrophobic counterions, provides a record‐breaking antenna effect ≈1000. However, the high dye cooperativity of its thousands of encapsulated dyes causes energy losses by traces of self‐quenched dye aggregates. Here, it is found that these imperfections can be suppressed by blank hydrophobic salts (BHS) formed by the same bulky counterion (fluorinated tetraphenylborate) with an optically inactive cation, analogs of ionic liquids. The presence of BHS increases twofold the fluorescence quantum yields and fluorescence lifetimes of NPs and suppresses their fluorescence blinking. This study assumes that BHS provides an excess of bulky counterions that excludes traces of dye aggregates. As a result, an efficient Forster resonance energy transfer (FRET) is achieved from 40 000 dye donors to a single acceptor within a 70 nm particle, leading to the antenna effect of 4800, which is by far the highest value reported to date. Using this nanoantenna, a single‐molecule detection of the FRET acceptor is realized at low excitation power using an RGB camera of a smartphone.

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Size Matters! On the Way to Ionic Liquid Systems without Ion Pairing

Cited by 48 publications

References 64 publications

En route formation of ion pairs at the ionic liquid–vacuum interface

En route formation of ion pairs at the ionic liquid–vacuum interface

Ionic Liquids with Weakly Coordinating [M^III(OR^F)₄]⁻ Anions

Giant Light‐Harvesting in Dye‐Loaded Nanoparticles Enhanced by Blank Hydrophobic Salts

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Size Matters! On the Way to Ionic Liquid Systems without Ion Pairing

Cited by 48 publications

References 64 publications

En route formation of ion pairs at the ionic liquid–vacuum interface

En route formation of ion pairs at the ionic liquid–vacuum interface

Ionic Liquids with Weakly Coordinating [MIII(ORF)4]− Anions

Giant Light‐Harvesting in Dye‐Loaded Nanoparticles Enhanced by Blank Hydrophobic Salts

Contact Info

Product

Resources

About

Ionic Liquids with Weakly Coordinating [M^III(OR^F)₄]⁻ Anions