Charge‐Scaling Effect in Ionic Liquids from the Charge‐Density Analysis of N,N′‐Dimethylimidazolium Methylsulfate

The charge scaling effect in ionic liquids was explored on the basis of experimental and theoretical charge‐density analyses of [C₁MIM][C₁SO₄] employing the quantum theory of atoms in molecules (QTAIM) approach. Integrated QTAIM charges of the experimental (calculated) charge density of the cation and anion resulted in non‐integer values of ±0.90 (±0.87) e. Efficient charge transfer along the bond paths of the hydrogen bonds between the imidazolium ring and the anion was considered as the origin of these reduced charges. In addition, a detailed QTAIM analysis of the bonding situation in the [C₁SO₄]^? anion revealed the presence of negative π_O→σ*_S‐O hyperconjugation.     

Charge mosaic membranes prepared from laminated structures of PVA-based charged layers: 1. Preparation and transport properties of charged mosaic membranes

A charge mosaic (CM) membrane has high permselectivity for electrolytes. While there are many reports of attempts to prepare such membranes, it is difficult to make CM membranes for practical applications. We report the preparation of CM membranes from laminated structures of charged-poly(vinyl alcohol) (PVA) membranes. The membranes were prepared by alternately stacking negatively charged base membranes and positively charged base membranes and by cutting the stack of charged layers. Permeation experiments were performed in a dialysis system consisting of the membrane and mixed solutions of KCl and sucrose. Although the salt flux through the membrane was about 30 times less than that through the charge mosaic membrane Desalton^® (Tosoh Co. Ltd.), which was prepared using microphase separation, the permselectivity for salt of our membrane is more than 30 times higher than that of Desalton^®.     

Polylactide microspheres prepared by premix membrane emulsification—Effects of solvent removal rate

Polylactide microspheres were prepared by pre-mix membrane emulsification and subsequent extraction of solvent in a coagulation bath, and ultimately to the gas phase. The polymer was dissolved in dichloromethane and emulsified with water or water–methanol mixtures by repeated passage through a glass membrane. During and after emulsification, the droplets are exposed to a bath consisting of a mixture of water and methanol. Transfer of dichloromethane takes place into the bath and (subsequently) to the gas phase. Compared to water, the solubility of dichloromethane is increased when using water–methanol mixtures; the continuous phase can quickly dissolve a significant amount of the solvent, while transfer to the gas phase is strongly enhanced as well. This was observed experimentally and by computer simulation, using a combined model based on the Maxwell–Stefan theory for non-ideal, multi-component mass transfer.

With increasing methanol concentration, the size and span of the microspheres became smaller, and was approximately 1 μm at 30% methanol. The surface morphology of these particles was solid and smooth, whereas holes were observed in those prepared in pure water. At methanol concentrations higher than 30%, the size of the microspheres increased again. This is probably due to the swelling of the particles because of the high in-diffusion of methanol which increases the porosity of the particles. Our main conclusion is that particles of defined size and size distribution can be produced by simply adjusting the non-solvent composition of the pre-mix.     

Selectivity in anionic and cationic ring‐opening polymerizations of tetramethyl‐1‐(3′‐trifluoromethylphenyl)‐1‐phenylcyclotrisiloxane and tetramethyl‐1‐[3′,5′‐bis(trifluoromethyl)phenyl]‐1‐phenylcyclotrisiloxane

Anionic and cationic ring‐opening polymerizations of two novel cyclotrisiloxanes, tetramethyl‐1‐(3′‐trifluoromethylphenyl)‐1‐phenylcyclotrisiloxane ( I ) and tetramethyl‐1‐[3′,5′‐bis(trifluoromethyl)phenyl]‐1‐phenylcyclotrisiloxane ( II ), are reported. Anionic ring‐opening polymerization of I or II leads to copolymers with highly regular microstructures. Copolymers obtained by cationic polymerizations of I or II , initiated by triflic acid, have less regular microstructures characteristic of chemoselective polymerization processes. The composition and microstructure of copolymers have been characterized by ¹H and ²⁹Si‐NMR, the molecular weight distributions by GPC, and the thermal properties by DSC and TGA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5235–5243, 2004     

Charge‐carrier transport in disordered polymers

The general properties of charge‐carrier transport in disordered organic materials are discussed. The spatial correlation between energies of transport sites determined the form of drift‐mobility field dependence. The type of spatial correlation in a disordered material depends on its nature. Mobility field dependences must be different in polar and nonpolar materials. Different methods of mobility calculation from the shape of photocurrent transient were analyzed. A widely used method is very sensitive to the variation of the shape of the transient and sometimes produces results that effectively masquerade the true dependence of the mobility on the electric field or trap concentration. Arguments in favor of the better, more reliable method are suggested. Charge transport in materials containing charged traps was considered without using the isolated trap approximation, and this led to qualitatively different results. The results indicated that the effect of charged traps can hardly be responsible for the experimentally observed transport properties of disordered organic materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2584–2594, 2003     

Ionic Ingress and Charge‐Neutralization Phenomena of Conducting‐Polymer Films

Ionic ingress and diffusion through a conducting‐polymer (CP) film containing embedded charges under potential and concentration gradients is studied. Electroneutrality, a common assumption in modeling of similar systems, is not justified in this case or similar diffusion‐limited processes, as the timescale of ionic diffusion in the solid matrix is quite large. Counter ions therefore cannot move instantaneously for effective neutralization of excess charges. Poisson–Nernst–Planck (PNP) equations have to be solved for such cases without any simplifying assumption. Analytical solution shows the existence of a charge boundary layer, which limits and strongly influences the ionic flux. A general numerical method for solution is also developed for the dynamic modeling, analysis, and design of these types of systems. The numerical results are validated by comparison with analytical solutions as well as with some experimental results available in the literature. With this modeling framework, the basic features of controlled release of molecules across a CP film under an applied electrical potential can be explained quantitatively.     

Charge‐transfer piperazine‐containing polymeric systems via ring‐opening metathesis polymerization

This article describes the synthesis of piperazine‐containing homopolymer systems via ring‐opening metathesis polymerization (ROMP). These systems were subsequently used as electron donors in the formation of charge‐transfer (CT) complexes. Using exo‐N‐(6‐bromohexyl)‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxamide as a starting material, monomers were synthesized to act as electron donors. The amine group at the “open” end of the piperazine was either left open or alkylated with various alkyl groups. The monomers' ability to act as electron donors and their polymerization rates were studied. After initial photometric titration studies using 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ) as an electron acceptor proved that these monomers would act as electron donors, they were subsequently polymerized into homopolymers via ROMP. The experimental results showed that a methanol:chloroform mixed solvent system enhanced the rate of polymerization over a single solvent (chloroform) system. Studies also showed that the alkylated piperazine‐containing monomer had a faster rate of polymerization than the secondary piperazine monomer. These monomers were used to make piperazine‐containing homopolymers via ROMP and the resulting polymers, like the monomers, also functioned as electron donors. Potential functions of these polymers include electronics, solar cells, optical systems, and biological applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5034–5043, 2009     

Ring‐Opening and polymerization of 1‐[2′‐(heptaphenylcyclotetrasiloxanyl)ethyl]‐1,3,3,5,5‐pentamethylcyclotrisiloxane

1‐[2′‐(Heptaphenylcyclotetrasiloxanyl)ethyl]‐1,3,3,5,5‐pentamethylcyclotetrasiloxane ( II ) was prepared from 1‐[2′‐(methyldichlorosilyl)ethyl]‐1,3,3,5,5,7,7‐heptaphenylcyclotetrasiloxane ( I ) and tetramethyldisiloxane‐1,3‐diol. Acid‐catalyzed ring‐opening of II in the presence of tetramethyldisiloxane gave 1,9‐dihydrido‐5‐[2′‐(heptaphenylcyclotetrasiloxanyl)ethyl]nonamethylpentasiloxane ( III ) and 1,9‐dihydrido‐3‐[2′‐(heptaphenylcyclotetrasiloxanyl)ethyl]nonamethylpentasiloxane ( IV ). Both acid‐ and base‐catalyzed ring‐opening polymerization of II gives highly viscous, transparent polymers. The structures of I – IV and polymers were determined by UV, IR, ¹H, ¹³C, and ²⁹Si NMR spectroscopy. In addition, molecular weights obtained by GPC and NMR end group analysis were confirmed with mass spectrometry. On the basis of ²⁹Si NMR spectroscopy, the polymers appear to result exclusively from ring‐opening of the cyclotrisiloxane ring. No evidence for ring‐opening of the cyclotetrasiloxane ring was observed. Polymer properties were determined by DSC and TGA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 137–146, 2006     

Well‐Defined Flexible Polyelectrolytes with Two Cationic Sites per Monomeric Unit

Summary: Well‐defined flexible, annealed, and quenched polyelectrolytes with two cationic sites per monomeric unit are synthesized. The synthetic scheme involves the synthesis of narrowly distributed poly(p‐tert‐butoxystyrene) precursors by anionic polymerization high vacuum techniques, hydrolysis to poly(p‐hydroxystyrene), and subsequent quantitative functionalization by a Mannich‐type reaction, to yield annealed polyelectrolytes with two dimethylamino groups per monomer. In a last step, the dimethylamino groups are converted into quaternary ammonium salts by reaction with methyl iodide to give high‐charge‐density quenched cationic polyelectrolytes. The polymers are molecularly characterized by NMR and FT‐IR spectroscopy, while their solution behavior is studied by potentiometric titrations, turbidimetry, and fluorescence spectroscopy as a function of pH, in the case of the annealed polyelectrolytes, as well as by viscometry in the case of the quenched polyelectrolytes.

Schematic diagram of the synthesis of the polyelectrolytes.     

A Charge‐Transfer‐Induced Self‐Healing Supramolecular Hydrogel

In this study, a dual‐component charge‐transfer (CT)‐induced supramolecular hydrogel was fabricated using pyrene‐tailored pyridinium (PYP) and 2,4,7‐trinitrofluorenone (TNF) as the electron donor and acceptor, respectively. Its thermal stability and mechanical property have been modulated effectively by altering the concentration or molar ratio of PYP and TNF. Moreover, this CT hydrogel exhibited a distinct injectable self‐healing property that could be utilized to create desired patterns on substrates. Such property holds potential for this CT hydrogel in fields like three‐dimensional printing and surface coating.     

Symmetry‐Breaking Charge‐Transfer Chromophore Interactions Supported by Carbon Nanodots

Carbon dots (CDs) and their derivatives are useful platforms for studying electron‐donor/acceptor interactions and dynamics therein. Herein, we couple amorphous CDs with phthalocyanines (Pcs) that act as electron donors with a large extended π‐surface and intense absorption across the visible range of the solar spectrum. Investigations of the intercomponent interactions by means of steady‐state and pump‐probe transient absorption spectroscopy reveal symmetry‐breaking charge transfer/separation and recombination dynamics within pairs of phthalocyanines. The CDs facilitate the electronic interactions between the phthalocyanines. Thus, our findings suggest that CDs could be used to support electronic couplings in multichromophoric systems and further increase their applicability in organic electronics, photonics, and artificial photosynthesis.     

Covalent immobilization of albumin on micron‐sized magnetic poly(methyl methacrylate‐divinylbenzene‐glycidyl methacrylate) microspheres prepared by modified suspension polymerization

Micron‐sized magnetic poly(methyl methacrylate‐divinylbenzene‐glycidyl methacrylate) microspheres were prepared by a modified suspension polymerization in the presence of oleic acid‐coated magnetite nanoparticles. The magnetic microspheres were functionalized by reacting the epoxy groups with ammonia solution to provide amino groups. After activated with glutaraldehyde (GA), bovine serum albumin was covalently immobilized on these magnetic microspheres. The influence of initial protein concentration, pH and ionic strength of the protein solution on covalent immobilization was studied. Scanning electron micrographs showed that the magnetic microspheres had an average size of 6.4 µm and relative narrow size distribution. Magnetic measurement revealed the magnetic microspheres were superparamagetic with saturation magnetization of 7.32 emu/g. The successful amination of the magnetic microspheres was confirmed by Fourier transform infrared spectroscopy (FT‐IR). Copyright © 2005 John Wiley & Sons, Ltd.     

Nature of Noncovalent Carbon‐Bonding Interactions Derived from Experimental Charge‐Density Analysis

In an effort to better understand the nature of noncovalent carbon‐bonding interactions, we undertook accurate high‐resolution X‐ray diffraction analysis of single crystals of 1,1,2,2‐tetracyanocyclopropane. We selected this compound to study the fundamental characteristics of carbon‐bonding interactions, because it provides accessible σ holes. The study required extremely accurate experimental diffraction data, because the interaction of interest is weak. The electron‐density distribution around the carbon nuclei, as shown by the experimental maps of the electrophilic bowl defined by a (CN)₂C?C(CN)₂ unit, was assigned as the origin of the interaction. This fact was also evidenced by plotting the Δ²ρ(r) distribution. Taken together, the obtained results clearly indicate that noncovalent carbon bonding can be explained as an interaction between confronted oppositely polarized regions. The interaction is, thus electrophilic–nucleophilic (electrostatic) in nature and unambiguously considered as attractive.     

Fullerol–Titania Charge‐Transfer‐Mediated Photocatalysis Working under Visible Light

The development of visible‐light‐active photocatalysts is being investigated through various approaches. In this study, C₆₀‐based sensitized photocatalysis that works through the charge transfer (CT) mechanism is proposed and tested as a new approach. By employing the water‐soluble fullerol (C₆₀(OH)_x) instead of C₆₀, we demonstrate that the adsorbed fullerol activates TiO₂ under visible‐light irradiation through the “surface–complex CT” mechanism, which is largely absent in the C₆₀/TiO₂ system. Although fullerene and its derivatives have often been utilized in TiO₂‐based photochemical conversion systems as an electron transfer relay, their successful photocatalytic application as a visible‐light sensitizer of TiO₂ is not well established. Fullerol/TiO₂ exhibits marked visible photocatalytic activity not only for the redox conversion of 4‐chlorophenol, I^?, and Cr^VI, but also for H₂ production. The photoelectrode of fullerol/TiO₂ also generates an enhanced anodic photocurrent under visible light as compared with the electrodes of bare TiO₂ and C₆₀/TiO₂, which confirms that the visible‐light‐induced electron transfer from fullerol to TiO₂ is particularly enhanced. The surface complexation of fullerol/TiO₂ induced a visible absorption band around 400–500 nm, which was extinguished when the adsorption of fullerol was inhibited by fluorination of the surface of TiO₂. The transient absorption spectroscopic measurement gave an absorption spectrum ascribed to fullerol radical cations (fullerol^.+) the generation of which should be accompanied by the proposed CT. The theoretical calculation regarding the absorption spectra for the (TiO₂ cluster+fullerol) model also confirmed the proposed CT, which involves excitation from HOMO (fullerol) to LUMO (TiO₂ cluster) as the origin of the visible‐light absorption.     

pH‐Triggered Charge‐Reversal Polyurethane Micelles for Controlled Release of Doxorubicin

A series of pH‐triggered charge‐reversal polyurethane copolymers (PS‐PUs) containing methoxyl‐poly(ethylene glycol) (mPEG), carboxylic acid groups, and piperazine groups is presented in this work. The obtained PS‐PUs copolymers can form into stable micelles at pH 7.4, which response to a narrow pH change (5.5–7.5) and show a tunable pH‐triggered charge‐reversal property. Doxorubicin (DOX) is encapsulated into the PS‐PU micelles as a model drug. The drug release of DOX‐loaded PS‐PU micelles shows an obviously stepped‐up with reducing the pH. Meanwhile, it is found that the charge‐reversal property can improve the cellular uptake behavior and intracellular drug release in both HeLa cells and MCF‐7 cells. Additionally, the time‐dependent cytotoxicity of the DOX‐loaded PS‐PU micelles is confirmed by MTT assay. Attributed to the tunable charge‐reversal property through changing the molar ratio of piperazine/carboxyl, the PS‐PU micelles will be a potential candidate as an intelligent drug delivery system in future studies.

     

Synthesis and Plasmon‐Induced Charge‐Transfer Properties of Monodisperse Gold‐Doped Titania Microspheres

Functional spheres : Monodisperse gold‐doped titania spheres with tunable sizes under high concentration of titanium precursor have been synthesized by introducing trace amounts of chloroauric acid into the reaction system. Surface photovoltage, surface photocurrent, and transient photovoltage measurements (see figure) of annealed samples reveal that gold nanodots can act as both electron acceptors and donors under the illumination of different wavelengths of light.

     

A Photoisomerization‐Activated Intramolecular Charge‐Transfer Process for Broadband‐Tunable Single‐Mode Microlasers

Miniaturized lasers with high spectral purity and wide wavelength tunability are crucial for various photonic applications. Here we propose a strategy to realize broadband‐tunable single‐mode lasing based on a photoisomerization‐activated intramolecular charge‐transfer (ICT) process in coupled polymer microdisk cavities. The photoisomerizable molecules doped in the polymer microdisks can be quantitatively transformed into a kind of laser dye with strong ICT character by photoexcitation. The gain region was tailored over a wide range through the self‐modulation of the optically activated ICT isomers. Meanwhile, the resonant modes shifted with the photoisomerization because of a change in the effective refractive index of the polymer microdisk cavity. Based on the synergetic modulation of the optical gain and microcavity, we realized the broadband tuning of the single‐mode laser. These results offer a promising route to fabricate broadband‐tunable microlasers towards practical photonic integrations.