Solvents Of Low Dielectric Constant Research Articles

(Invited) Probing Charge Carrier-Induced Changes in the Complex Dielectric Function in Carbon Nanotube Dispersions

The injection of charge carriers into pi-conjugated semiconductors, whether by electrochemical injection or chemical charge transfer, is a powerful approach to tune their electrical conductivity. Recently, the concept of dielectric catastrophe, where the charge carrier density is sufficiently large to significantly alter the intrinsic dielectric properties, has been demonstrated at high doping levels in organic semiconductor thin films. The observed increase in the dielectric constant leads to reduced coulombic interactions between charge carriers and the associated counterions, promoting enhanced free carrier generation and transport.Here, we employ a combination of steady state optical spectroscopy, quantitative 19F NMR studies, and microwave dielectric loss spectroscopy to probe charge carrier density and transport in doped single-walled carbon nanotube dispersions. We demonstrate that a similar dielectric catastrophe phenomenon can be observed even in isolated single-walled carbon nanotubes dispersed in a low dielectric constant solvent AND, perhaps more surprisingly, at carrier densities less than one carrier per nanotube. The precise details of the observed changes in complex dielectric function are dependent on the chemical structure of the charge-transfer dopant, with a near-instantaneous increase in the dielectric constant and electrical conductivity observed for low carrier densities using bulky benzyloxy-substituted icosahedral dodecaborane cluster dopants, DDBs. We attribute the observations to weak coulombic interactions between the injected charge carrier and the dopant counterion, along with the large polarizability afforded by the unique physicochemical properties of single-walled carbon nanotubes. If time permits, we will show results from recent studies where we extend this approach to the doping of other nanocarbons.

Counterion Effects in [Ru(bpy)3](X)2-Photocatalyzed Energy Transfer Reactions.

Photocatalysis that uses the energy of light to promote chemical transformations by exploiting the reactivity of excited-state molecules is at the heart of a virtuous dynamic within the chemical community. Visible-light metal-based photosensitizers are most prominent in organic synthesis, thanks to their versatile ligand structure tunability allowing to adjust photocatalytic properties toward specific applications. Nevertheless, a large majority of these photocatalysts are cationic species whose counterion effects remain underestimated and overlooked. In this report, we show that modification of the X counterions constitutive of [Ru(bpy)3](X)2 photocatalysts modulates their catalytic activities in intermolecular [2 + 2] cycloaddition reactions operating through triplet-triplet energy transfer (TTEnT). Particularly noteworthy is the dramatic impact observed in low-dielectric constant solvent over the excited-state quenching coefficient, which varies by two orders of magnitude depending on whether X is a large weakly bound (BArF 4 -) or a tightly bound (TsO-) anion. In addition, the counterion identity also greatly affects the photophysical properties of the cationic ruthenium complex, with [Ru(bpy)3](BArF 4)2 exhibiting the shortest 3MLCT excited-state lifetime, highest excited state energy, and highest photostability, enabling remarkably enhanced performance (up to >1000 TON at a low 500 ppm catalyst loading) in TTEnT photocatalysis. These findings supported by density functional theory-based calculations demonstrate that counterions have a critical role in modulating cationic transition metal-based photocatalyst potency, a parameter that should be taken into consideration also when developing energy transfer-triggered processes.

Computational insight towards the binding affinity and participation of aliphatic unsaturated sidearms of aza-18-crown-6 extractants for Sr2+ encapsulation in different solvent medium.

Macrocyclic extractants capture cations in solution phase; therefore, their structures and energetics in different solvents are worth investigating. In this computational research work, the optimized geometry of three aza-18-crown-6 extractants (1-3) has been obtained in suitable solvent mediums to work out the influence of the solvation on their binding affinity with Sr2+. The designed macrocyclic extractants are remarkable as the N-substituted side chain bears the rarely examined simple aliphatic unsaturated double and triple bond. All significant structural perturbations of the macro ring wherein Sr2+ binds are examined. Prediction of the auxiliary effect of the simple aliphatic unsaturated side arm on the binding of Sr2+ through solvent competition or cation-pi interaction is undertaken. The binding affinity of the complex formed in the solvent and gas phases is calculated. Results obtained in this study favor the utilization of solvents of low dielectric constant (CHCl3 and DCM) for effective binding of Sr2+ ions by the extractants. All DFT calculations were performed using the Gaussian 09 program. The optimized geometries and their structural features were visualized by GaussView. Density functional calculation involving B3LYP functional and LANL2DZ basis set was employed to obtain optimized geometry and energy of the extractants and their Sr2+ complex. The solvation effects were considered by employing the calculations with the polarized continuum model (PCM). The computational method's reliability was assured by comparing the optimized structure with that of X-ray reported structure of a similar type of complex.

Facile purification protocol of CsPbBr3 nanocrystals for light-emitting diodes with improved performance

Light-emitting diodes (LEDs) based on CsPbBr3 nanocrystals (NCs) show excellent performance in terms of external quantum efficiency (EQE) and brightness. Removal of impurities after NC synthesis is a necessary and critical step to achieve such high performance. In fact, the optical and electronics properties of CsPbBr3 NCs are greatly affected by how the NCs are purified from the synthetic by-products, unreacted reagents, and organic ligand excess. Perovskite NC purification protocols must consider the ionic nature of the inorganic core, the labile nature of the ligand to surface bond, and the dynamic equilibrium between the surface-interacting and free form organic ligands to prevent NC damaging with subsequent loss of photoluminescence. Nowadays, the most employed purification protocol involves NC precipitation based on a diminished non-polar environment achieved by adding a low-dielectric constant miscible solvent to the NC solution (i.e., ethyl acetate to toluene), followed by redispersion of the precipitate in a storage solvent. Here, we explored the possibility to precipitate impurities left in the NC solution exploiting variations in solubility at decreasing temperature: by taking NC solutions at −20 °C overnight and by collecting the respective supernatant we obtain CsPbBr3 NC solutions which leads to LEDs with improved EQE. The freezing process at −20 °C gives rise to NC solutions that retain the pristine optical and electronic properties while the LED performances display a 3 times increase in terms of EQE (EQEmax = 8.9%) with respect to NCs treated with anti-solvent only. Finally, we show that our purification protocol can be applied to CsPbBr3 NCs obtained via different synthetic methods, thus demonstrating the versatility of our facile purification protocol.

Can hydrogen anion be a possible intermediate of the hydrogen electrode reaction?

• New mechanism for the hydrogen evolution reaction (HER) proposed. • Hydride anion formation investigated as possible reaction intermediate. • Potential range of stability of hydride anion depends on work function of electrode. • Potential range of stability of hydride anion depends on dielectric constant of solvent. • Rate determining term approach used to predict Tafel slope of HER. We discuss the possibility of a new mechanism for the hydrogen evolution reaction (HER) involving hydrogen anion as the reaction intermediate. A simple thermodynamic analysis reveals that this mechanism is unfavourable at most relevant catalysts in aqueous solution in the usual potential range encountered for the HER. Its likelihood, however, increases when the dielectric permittivity of the electrolyte solution decreases, the work function of the catalyst decreases, and when the electrode potential decreases. We suggest that carbon-based catalysts with low dielectric constant solvents, such as n -Hexane, are plausible systems to observe hydrogen anion as the intermediate for hydrogen reactions. In the cases where the proposed HER mechanism is permissible, values of Tafel slope are calculated using a simple kinetic analysis based on the rate-determining term concept.

Solubility determination and thermodynamic modelling of Progesterone in twelve pure solvents and three binary solvents at 278.15 to 323.15 K

The solubility of Progesterone at T = 278.15–323.15 K was measured by static equilibrium method combined with HPLC in twelve solvents (methanol, ethanol, isopropanol, n-propanol, n-butanol, acetone, tetrahydrofuran, 1,4-dioxane, n-heptane, ethyl acetate, acetonitrile, and toluene) and three binary solvents (tetrahydrofuran + n-heptane, 1,4-dioxane + n-heptane, and toluene + n-heptane). The results showed that progesterone has the highest solubility in toluene (0.2249 in mole fraction) and other low-dielectric constant solvents, and the smallest in n-heptane (1.120 × 10−4 in mole fraction). Moreover, the solubility increases as the temperature rise both in pure and mixed solvents. As expected, the DSC and XRDP results showed that there was no crystal form difference between the raw material and all the precipitate. Herein, the Modified Apelblat model, Buchowski-Ksiazaczak λh model, Jouyban-Acree model, CNIBS/R-K model, and SUN model were employed to fit the experimental data. As a result, the maximum RAD doesn't exceed 5.0%, and the maximum RMSD was less than 0.1%. Furthermore, we chose KAT-LSER model to explore the solubility of progesterone and the solute-solvent interaction relationships. The results showed that when hydrogen bond acidity and polarizability/dipolarity of solvents increases, the solubility of progesterone increases. Meanwhile, comparing the experimental data and the fitting results, it can be concluded that the experimental data was reliable and almost consistent with the fitting results. Furthermore, it also proved that the above mentioned five thermodynamic equations were advantageous and trustworthy.

Transition-State Expansion: A Quantitative Model for Counterion Effects in Ionic Reactions.

SummaryIonic reactions are the most common reactions used in chemical synthesis. In relatively low dielectric constant solvents (e.g., dichloromethane, toluene), ions usually exist as ion pairs. Despite the importance of counterions, a quantitative description of how the paired 'counterion' affects the reaction kinetic is still elusive. We introduce a general and quantitative model, namely transition-state expansion (TSE), that describes how the size of a counterion affects the transition-state structure and the kinetics of an ionic reaction. This model could rationalize the counterion effects in nucleophilic substitutions and gold-catalyzed enyne cycloisomerizations.

Reversible Symmetry-Breaking Charge Separation in a Series of Perylenediimide Cyclophanes

Excited-state symmetry-breaking charge separation (SB-CS) can offer an efficient pathway to solar energy capture and conversion. We synthesized a series of 1,6,7,12-tetrakis(4-t-butylphenoxy)perylene(3,4:9,10)bis(dicarboximide) cyclophane dimers with m-xylylene, p-xylylene, and 4,4′-diyldimethane-1,1′-biphenyl spacers and studied them with steady-state and time-resolved optical spectroscopies. Photoinduced SB-CS occurs in all three cyclophanes in CH2Cl2, with the SB-CS rate decreasing as the interchromophore distance is increased. Time-resolved emission spectroscopy and kinetic modeling reveal that the charge-separated state exists in pseudoequilibrium with the excited state prior to decay. Notably, the meta-spaced cyclophane also undergoes SB-CS in toluene within ∼100 ps, despite the lack of charge stabilization by the low dielectric constant solvent. These results demonstrate that SB-CS can occur across long distances and in weakly polar environments, which offers the possibility of harnessing SB-CS for solar energy capture and conversion.

Photo-Rechargeable Perovskite Cell for Direct Solar Energy Conversion and Storage

Perovskite solar cells (PSCs) are remarkably efficient. Recent years have witnessed a surge in PSC researches in both material development and structure optimization. In a PSC, a lead halide perovskite absorber is typically sandwiched between layers of hole and electron transport materials (i.e., HTM and ETM, respectively) to facilitate the extraction of photoexcited charges, but this may also create issues of energy level mismatch and interfacial degradation. A critical challenge for both HTM and ETM materials is the ineffective charge collection because of their incompatible work functions with the perovskite, which causes significant efficiency loss. In addition, the electron mobility of an ETM doesn’t typically match with the hole mobility in an HTM, leading to interfacial charge accumulation, hysteresis and degradation. There have been extensive efforts in developing materials via work-function modulation and interfacial treatment; however, they are expensive and challenging, and may not be compatible with the solution processing of the perovskite. In this work, we demonstrated replacing HTM and ETM with two pairs of nonaqueous redox couples to extract charges from the perovskite-electrolyte interfaces through photoelectrochemical or electrochemical reactions. These redox couples, dissolved in a low dielectric constant solvent, are not only to fully encapsulate and stabilize the perovskite, but also offer easy fine-tuning of their electrochemical properties to match with the perovskite. Most importantly, the nonaqueous redox couples serve as efficient energy media and solar energy can be directly converted/stored into chemical energy at the point of solar energy generation without the intermediate step such as electricity. Recent progress will be discussed and the intricate interplay between the perovskite layer morphology and redox couples will be presented.

Structural and surface properties control the recovery and purity of bio- hyaluronic acid upon precipitation with isopropyl alcohol

Microbial hyaluronic acid (bio-HA) is a highly valued product due to its wide range of aesthetic and medical applications. High purity is an essential requirement for those applications. HA is a polyelectrolyte susceptible to structural changes with pH; therefore, precipitation with organic solvents is attractive as a downstream processing step. However, its high hydration capacity requires a low dielectric constant solvent such as isopropyl alcohol (IPA) for better performance. Although precipitation is a typical step of polymer purification, there is still a lack of data relating the changes in the colloidal domain to precipitation performance. Therefore, this work examined the changes in zeta potential (ZP) surface tension (ST) and hydrodynamic size (HS) as functions of pH before and after bio-HA precipitations with IPA from a culture medium containing soy peptone (SP) as the main contaminant. The results showed that the structural and surface changes mediated by pH as well as the proportion of IPA:broth were correlated with the recovery and purity of bio-HA. The best results for recovery (R) and purity (P) were obtained at 2:1 IPA/broth v/v with 76.0 ± 6.6% (R) and 79.0 ± 1.8% (P) at pH 3, as well as 72.0 ± 7.5% (R) and 74.0 ± 2.7% (P) at pH 7. These findings are relevant for a better understanding of the interactions at the colloidal level that lead to the optimization of the bio-HA precipitation step based on the structural and surface properties.

The Interplay between Salt Association and the Dielectric Properties of Low Permittivity Electrolytes: The Case of LiPF6 and LiAsF6 in Dimethyl Carbonate

In this article, we present evidence that the dielectric constant of an electrolyte solution can be effectively used to infer the association regime of the salt species from computational methods. As case studies, we consider the low dielectric constant solvent dimethyl carbonate with LiAsF6 and LiPF6 salts at low concentrations. Using both quantum “ab initio” methods as well classical molecular dynamics simulations, we elucidate the salt’s contribution to the dielectric constant as well as the dipolar relaxation times, which act as quantitative signatures. By comparing to previously published measurements, we provide strong evidence for the presence of contact-ion pairs at these low concentrations. Interestingly, these ion pairs increase the dielectric constant of the solution, allowing for significantly improved ionic conductivity as a function of salt concentrations. We also discuss the role of multimeric equilibrium species as contributors to the functional properties of designer electrolytes, such as...

Hunting mermaids in real space: known knowns, known unknowns and unknown unknowns.

We review efforts to realise so-called mermaid (or short-ranged attraction/long ranged repulsion) interactions in 3d real space. The repulsive and attractive contributions to these interactions in charged colloids and colloid-polymer mixtures, may be accurately realised, by comparing particle-resolved studies with colloids to computer simulation. However, when we review work where these interactions have been combined, despite early indications of behaviour consistent with predictions, closer analysis reveals that in the non-aqueous systems used for particle-resolved studies, the idea of summing the attractive and repulsive components leads to wild deviations with experiment. We suggest that the origin lies in the weak ion dissociation in these systems with low dielectric constant solvents. Ultimately this leads even to non-centro-symmetric interactions and a new level of complexity in these systems.

Synergism from interfaces between Cu and crystalline ZrO2 nanosheets fabricated by acetic complex method for oxalates hydrogenation

Herein, the Cu species uniformly combining with highly crystalline ZrO2 nanosheets had been prepared by a one-pot acetic complex method. The selectivity to ethylene glycol of 98.9%, which corresponds to 99.8% conversion of diethyl oxalate was obtained over the one prepared by using acetic acid (AC) both as the complex agent and solvent. In addition, a stable performance was achieved (life span of >160h). It also showed good performance in hydrogenation of dimethyl oxalate (95.7h−1 turnover frequency). Essentially, solvents with different dielectric constant employed in complexation process had a prominent influence on the structure and catalytic activity of Cu/ZrO2 catalyst via solvation. Besides, complexation process was also important since AC could be regarded as L-type ligands in a low dielectric constant solvent, forming of ion-clusters which resulted in exclusive formation of the Cu-O-Zr interface after calcination. Evidently, the surface synergistic effect held the key to the continuous hydrogenation reaction related to the activation of the carbonyl groups and the hydrogen dissociation, thus creating a synergetic nanoenvironment for the successful completion of the “multi step turning into one-step” in the series reaction.

Wide-Temperature Electrolytes for Lithium-Ion Batteries.

Formulating electrolytes with solvents of low freezing points and high dielectric constants is a direct approach to extend the service-temperature range of lithium (Li)-ion batteries (LIBs). In this study, we report such wide-temperature electrolyte formulations by optimizing the ethylene carbonate (EC) content in the ternary solvent system of EC, propylene carbonate (PC), and ethyl methyl carbonate (EMC) with LiPF6 salt and CsPF6 additive. An extended service-temperature range from -40 to 60 °C was obtained in LIBs with lithium nickel cobalt aluminum oxide (LiNi0.80Co0.15Al0.05O2, NCA) as cathode and graphite as anode. The discharge capacities at low temperatures and the cycle life at room temperature and elevated temperatures were systematically investigated together with the ionic conductivity and phase-transition behaviors. The most promising electrolyte formulation was identified as 1.0 M LiPF6 in EC-PC-EMC (1:1:8 by wt) with 0.05 M CsPF6, which was demonstrated in both coin cells of graphite∥NCA and 1 Ah pouch cells of graphite∥LiNi1/3Mn1/3Co1/3O2. This optimized electrolyte enables excellent wide-temperature performances, as evidenced by the high capacity retention (68%) at -40 °C and C/5 rate, significantly higher than that (20%) of the conventional LIB electrolyte, and the nearly identical stable cycle life as the conventional LIB electrolyte at room temperature and elevated temperatures up to 60 °C.

Fabrication of TiO2 Nanoparticles by Electrostatic Jet Using the Low Dielectric Constant Solvent

Fabrication of TiO<SUB>2</SUB> Nanoparticles by Electrostatic Jet Using the Low Dielectric Constant Solvent

Optical Properties of Benzotriazole-Based Conjugated Polyelectrolytes

A series of conjugated polyelectrolytes (CPEs) based on an electron-deficient polybenzotriazole backbone with various pendant ionic functionalized side chains were synthesized directly from the corresponding ionic monomers. Of particular interest was to use the different chemical structures to understand how the optical features are influenced by the ionic side chains. We found that interchain aggregation is favored in low dielectric constant solvents for cationic CPEs. Moreover, aggregated species absorb at longer wavelengths and exhibit higher fluorescence quantum yields.

Proton transfer rate‐equilibria in apolar aprotic solvents: a historical perspective

Low dielectric constant apolar aprotic solvents, although employed on a limited scale for studying proton transfer reactions as compared with commonly used polar protic or dipolar aprotic ones, offer some particular advantages, namely, specific solute–solvent interactions are virtually eliminated and proton transfer occurs directly in an apolar aprotic solvent. An intriguing feature of these reactions is their general acid‐catalyzed/base‐catalyzed kinetics with a time scale over microseconds to minutes. In fact, the true or intrinsic relative strengths of acids/bases when measured in such solvents come to the fore much more clearly than those obtained in other classes of solvents. Recently, a review documenting the post‐1980 developments relating to proton transfer reactions in apolar aprotic solvents has been published. The present article is a commentary of the pre‐1980 developments in this area since the 1920s Brønsted–Lowry's “proton cult” of acid–base theory. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Water-assisted stable dispersal of graphene oxide in non-dispersible solvents and skin formation on the GO dispersion

Graphene oxide (GO) particles disperse well in a few polar solvents including water but do not disperse in non-polar and low dielectric constant solvents. The limitation of available solvents can restrict the application of GO compositional materials. Herein, we report that by adding small amount of water in a water-miscible solvent, the dispersity of GO can be significantly improved. The scheme works even in solvent with low dielectric constant; the water-added dioxane exhibited even better GO dispersity than pure water that is known to be the best solvent for GO dispersion to date. The method increases the spectrum of available solvents for dispersing GO particles. We also report a formation of skin layer with random birefringent wrinkles on the surface of water-dioxane binary GO dispersion. The skin layer in gel phase was partially stretchable and less rigid as compared to a fully dried GO film.

Analyzing Benzene and Cyclohexane Emulsion Droplet Collisions on Ultramicroelectrodes.

We report the collisions of single emulsion oil droplets with extremely low dielectric constants (e.g., benzene, ε of 2.27, or cyclohexane, ε of 2.02) as studied via emulsion droplet reactor (EDR) on an ultramicroelectrode (UME). By applying appropriate potentials to the UME, we observed the electrochemical effects of single-collision signals from the bulk electrolysis of single emulsion droplets. Different hydrophobic redox species (ferrocene, decamethyl-ferrocene, or metalloporphyrin) were trapped in a mixed benzene (or cyclohexane) oil-in-water emulsion using an ionic liquid as the supporting electrolyte and emulsifier. The emulsions were prepared using ultrasonic processing. Spike-like responses were observed in each i-t response due to the complete electrolysis of all of the above-mentioned redox species within the droplet. On the basis of these single-particle collision results, the collision frequency, size distribution, i-t decay behavior of the emulsion droplets, and possible mechanisms are analyzed and discussed. This work demonstrated that bulk electrolysis can be achieved in a few seconds in these attoliter reactors, suggesting many applications, such as analysis and electrosynthesis in low dielectric constant solvents, which have a much broader potential window.

Anomalous Capacitance Maximum of the Glassy Carbon-Ionic Liquid Interface through Dilution with Organic Solvents.

We use electrochemical impedance spectroscopy to measure the effect of diluting a hydrophobic room temperature ionic liquid with miscible organic solvents on the differential capacitance of the glassy carbon-electrolyte interface. We show that the minimum differential capacitance increases with dilution and reaches a maximum value at ionic liquid contents near 5-10 mol% (i.e., ∼1 M). We provide evidence that mixtures with 1,2-dichloroethane, a low-dielectric constant solvent, yield the largest gains in capacitance near the open circuit potential when compared against two traditional solvents, acetonitrile and propylene carbonate. To provide a fundamental basis for these observations, we use a coarse-grained model to relate structural variations at the double layer to the occurrence of the maximum. Our results reveal the potential for the enhancement of double-layer capacitance through dilution.