Formation Of Charge-transfer Complex Research Articles

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Surface-modified ZrO2 nanoparticles with caffeic acid: Characterization and in vitro evaluation of biosafety for placental cells

The toxicity of hybrid nanoparticles, consisting of non-toxic components, zirconium dioxide nanoparticles (ZrO2 NPs), and caffeic acid (CA), was examined against four different cell lines (HTR-8 SV/Neo, JEG-3, JAR, and HeLa). Stable aqueous ZrO2 sol, synthesized by forced hydrolysis, consists of 3–4 nm in size primary particles organized in 30–60 nm in size snowflake-like particles, as determined by transmission electron microscopy and direct light scattering measurements. The surface modification of ZrO2 NPs with CA leads to the formation of an interfacial charge transfer (ICT) complex followed by the appearance of absorption in the visible spectral range. The spectroscopic observations are complemented with the density functional theory calculations using a cluster model. The ZrO2 NPs and CA are non-toxic against four different cell lines in investigated concentration range. Also, ZrO2 NPs promote the proliferation of HTR-8 SV/Neo, JAR, and HeLa cells. On the other hand, hybrid ZrO2/CA NPs induced a significant reduction of the viability of the JEG-3 cells (39 %) for the high concentration of components (1.6 mM ZrO2 and 0.4 mM CA).

Facile synthesis of acyloxy-containing fluorene-based Cardo polyimides with high optical transparency, fluorescence and low dielectric constant

A series of acyloxy-containing fluorene-based Cardo polyimides (PIs) were facilely synthesized by the post-polymerization modification based on a simple esterification of hydroxyl-containing PIs. Incorporation of acyloxy groups may reduce the packing density of PI chains and weaken both inter- and intra-chain charge transfer complexes (CTC) formation. Accordingly, the modified PIs exhibit the improved solubility in low-boiling-point solvents and optical transparence. The optical transmittance at 400 nm (T400) of all modified PI films is significantly increased to 80.1–83.5% from 41.6–54.5% of the precursor PI films. Meanwhile, the modified PI films exhibit a bright fluorescence. The modified PIs still display the superior heat resistance with a glass transition temperature (Tg) of 301.1–390.9 °C as well as admirable mechanical properties with a tensile strength (TS) of 72.1–81.3 MPa. In addition, the dielectric constant (k) value at 1 MHz of the modified PI films is decreased to 2.58–2.90 from 3.95–4.48 of the precursor PI films, which is attributed to the enlarged free volume and reduced water absorption afforded by the incorporation of acyloxy groups. This work provides an efficient post-polymerization modification approach to simultaneously affording the multifunctional PI films with high Tg, high T400 and low k, probably as the potential candidates for the practical application in display and microelectronic industries.

Light stimulated donor-acceptor forms charge transfer complex in chlorinated solvents

Light stimulated donor-acceptor forms charge transfer complex in chlorinated solvents

Chemical Oxidative Polymerization of Methylene Blue: Reaction Mechanism and Aspects of Chain Structure.

The kinetic regularities of the initial stage of chemical oxidative polymerization of methylene blue under the action of ammonium peroxodisulfate in an aqueous medium have been established by the method of potentiometry. It was shown that the methylene blue polymerization mechanism includes the stages of chain initiation and growth. It was found that the rate of the initial stage of the reaction obeys the kinetic equation of the first order with the activation energy 49 kJ · mol−1. Based on the proposed mechanism of oxidative polymerization of methylene blue and the data of MALDI, EPR, and IR spectroscopy methods, the structure of the polymethylene blue chain is proposed. It has been shown that polymethylene blue has a metallic luster, and its electrical conductivity is probably the result of conjugation over extended chain sections and the formation of charge transfer complexes. It was found that polymethylene blue is resistant to heating up to a temperature of 440 K and then enters into exothermic transformations without significant weight loss. When the temperature rises above 480 K, polymethylene blue is subject to endothermic degradation and retains 75% of its mass up to 1000 K.

Stimuli-Responsive Trimorphs and Charge-Transfer Complexes of a Twisted Molecular Donor.

Supramolecular self-assemblies and co-assemblies possess multiple noncovalent interactions, highly ordered structures, and multifunctional properties. Yet, the fundamental understanding of their "structure-property relationship" remains very challenging. Herein, two kinetically controlled supramolecular charge transfer (CT) complexes were conceptualized from a trimorphic molecular donor denoted as "twisted aromatic hydrocarbon" (TAH), with p-fluoranil (TFQ) and p-chloranil (TCQ) in water, organic solvent, and solvent-free methods. Elucidating their co-assembling mechanism revealed that segmentation of the TAH with molecules having planar deficient cores spontaneously formed a distinct "H-type mixed stack" and "J-type segregated stack", regulated by blue/red-shifted charge-transfer and π-π stacking including weak C-H···F and C-H···O noncovalent interactions. By utilizing the structural transformational ability of the self-assembled TAH, the mechanistic aspects for the rapid nanoscopic co-assembly formation were precisely demonstrated experimentally and theoretically. The trimorphs and co-crystals of TAH could be disassembled resulting in turn-on emission by applying various external stimuli and being repeatedly reconfigured, thus providing a unique structure-property relationship and new TAH-based materials. This unique concept offers color-specific polymorphism and CT-complex formation strategy involving a simple class of functional materials having cooperative network forming ability using the twisted molecular donor.

Benzophenone‐Functionalized Oligo(Amido Amine)/Iodonium Salt Systems as Visible Light Photoinitiators

AbstractTwo water soluble oligomeric photoinitiators (OAA‐B and OAA‐BP) were synthesized by first preparing an oligo(amido amine) (OAA) via aza‐Michael addition reaction of N,N’‐methylene bisacrylamide and 1,4‐diaminobutane, then carrying out another aza‐Michael addition reaction between OAA and 4‐benzoylphenyl acrylate for OAA‐B and also diethyl vinylphosphonate for OAA‐BP. Photopolymerization kinetics of 2‐hydroxyethyl methacrylate (HEMA) and HEMA: poly(ethylene glycol) diacrylate (PEGDA, Mn = 575) mixture initiated by these photoinitiators were monitored by real‐time FTIR spectrophotometer and photo‐DSC. These photoinitiators together with bis‐(4‐tert‐butylphenyl)‐iodonium hexafluorophosphate (Iod) have high polymerization efficiencies under UV and unexpectedly visible light exposure. The efficiency of the photoinitiators is based on two separate mechanisms, oxidative interaction between benzophenone group and Iod and charge transfer complex (CTC) formation between Iod and amines in OAA; verified by absorption, steady state photolysis, electron spin resonance and laser flash photolysis. The CTC formation mechanism was also studied by molecular modeling studies; and both mechanisms generating aryl radicals.

Unzipping Carbon Nanotube Bundles through NH-π Stacking for Enhanced Electrical and Thermal Transport.

Bundling of single-walled carbon nanotubes (SWCNTs) significantly undermines their superior thermal and electrical properties. Realizing stable, homogeneous, and surfactant-free dispersion of SWCNTs in solvents and composites has long been regarded as a key challenge. Here, we report amine-containing aromatic and cyclohexane molecules, which are common chain extenders (CEs) for epoxy curing in industry, can be used to effectively disperse CNTs. We achieve single-tube-level dispersion of SWCNTs in CE solvents, as demonstrated by the strong chirality-dependent absorption and photoluminescence emission. The SWCNT-CE dispersion remains stable under ambient conditions for months. The excellent dispersibility and stability are attributed to the formation of an n-type charge-transfer complex through the NH-π interaction between the amine group of CEs and the delocalized π bond of SWCNTs, which is confirmed by the negative Seebeck coefficient of the CE-functionalized SWCNT films, the red shift of the G band in the Raman spectra, and the NH-π peak in X-ray photoelectron spectroscopy. The high dispersibility of CEs significantly improves the electrical and thermal transport of macroscale CNT assemblies. The sheet resistance of the CE-dispersed SWCNT thin films reaches 161 Ω sq-1 at 80.8% optical transmittance after functional modification by HNO3. Moreover, the CEs cross-link CNTs and epoxy molecules, forming a pathway for phonon transport in CNT/epoxy nanocomposites. The thermal conductivity of the CE-CNT-epoxy composite is enhanced by 1850% compared with the original epoxy, which is the highest enhancement reported to date for CNT/epoxy nanocomposites. The CE-based NH-π interaction provides a new paradigm for the effective and stable dispersion of SWCNTs in a facile and scalable process.

Exploring the potential of thin films made from poly(imide-amide-sulfone)s for engineering applications

This work focuses on the thorough investigation of structure–assisted multifunctional properties of some poly(amide-imide-sulfone) films specifically designed to meet the technological needs. In this respect, the influence of structural parameters onto mechanical, optical, dielectric and gas transport properties was deeply explored along with some general characteristics, like chemical integrity, thermal stability and solid-state packing. The understudy tough and flexible films featuring amorphous state displayed good mechanical behavior, withstanding repeating bending or rolling. The sulfone groups reduced the charge transfer complex formation, and in some cases, increased transparency. The permittivity, dielectric loss and conductivity and their variation with frequency and temperature were studied along with γ and β secondary relaxations originating from small- and large-scale segmental motions. The permeability of CO2, O2 and N2 through these dense films along with diffusion and solubility coefficients and respective selectivities were measured and discussed in relation with the structural parameters.

Oxidative Damage of S‐Containing Amino Acids by the Environmental Radical NO3.: A Kinetic, Product and Computational Study

AbstractMethionine, cysteine and cystine, which were acetylated at the N‐terminus and methylated at the C‐terminus, react rapidly with the environmental nitrate radical (NO3.) with rate coefficients of 7.7×109, 3.4×109 and 2.0×109 M−1 s−1, respectively, in acetonitrile. Methionine (Ac−Met−OMe) is successively oxidized via the sulfoxide (Ac−MetO−Me) to the sulfone (Ac−MetO2−OMe), with the latter step being also extremely fast with a rate coefficient of 1.2×109 M−1 s−1. Computations predict formation of an initial charge transfer complex between NO3. and the S or SO moiety in Ac‐Met‐OMe, Ac‐MetO‐OMe and cystine (Ac−Cys(S−S)Cys‐OMe), respectively, which is followed by simultaneous S−O bond formation and NO2. expulsion. Calculations for the reaction of cysteine (Ac‐Cys‐OMe) with NO3. revealed side‐chain oxidation to give a thiyl radical or a sulfenic acid as likely pathways. These findings highlight the potential harmful impact of NO2./O3 pollution on S‐containing amino acid residues in peptides.

Radical Carboxylative Cyclizations and Carboxylations with CO2.

Carbon dioxide (CO2) is not only a greenhouse gas and a common waste product but also an inexpensive, readily available, and renewable carbon resource. It is an important one-carbon (C1) building block in organic synthesis for the construction of valuable compounds. However, its utilization is challenging owing to its thermodynamic stability and kinetic inertness. Although significant progress has been achieved, many limitations remain in this field with regard to the substrate scope, reaction system, and activation strategies.Since 2015, our group has focused on CO2 utilization in organic synthesis. We are also interested in the vast possibilities of radical chemistry, although the high reactivity of radicals presents challenges in controlling selectivity. We hope to develop highly useful CO2 transformations involving radicals by achieving a balance of reactivity and selectivity under mild reaction conditions. Over the past 6 years, we along with other experts have disclosed radical-type carboxylative cyclizations and carboxylations using CO2.We initiated our research by realizing the Cu-catalyzed radical-type oxytrifluoromethylation of allylamines and heteroaryl methylamines to generate valuable 2-oxazolidones with various radical precursors. Apart from Cu catalysis, visible-light photoredox catalysis is also a powerful method to achieve efficient carboxylative cyclization. In these cases, single-electron-oxidation-promoted C-O bond formation between benzylic radicals and carbamates is the key step.Since carboxylic acids exist widely in natural products and bioactive drugs and serve as important bulk chemicals in industry, we realized further visible-light-promoted carboxylations with CO2 to construct such chemicals. We have achieved the selective umpolung carboxylations of imines, enamides, tetraalkylammonium salts, and oxime esters by successive single-electron-transfer (SSET) reduction. Using this strategy, we have also realized the dearomative arylcarboxylation of indoles with CO2. In addition to the incorporation of 1 equiv of CO2 per substrate, we have recently developed a visible-light photoredox-catalyzed dicarboxylation of alkenes, allenes, and (hetero)arenes via SSET reduction, which allows the incorporation of two CO2 molecules into organic compounds to generate valuable diacids as polymer precursors.In addition to the two-electron activation of CO2, we sought to develop new strategies to realize efficient and selective transformations via single-electron activation of CO2. Inspired by the hypothetical electron-transfer mechanism of iron-sulfur proteins, we have realized the visible-light-driven thiocarboxylation of alkenes with CO2 using catalytic iron salts as promoters. The in-situ-generated Fe/S complexes are likely able to reduce CO2 to its radical anion, which could react with alkenes to give a stabilized carbon radical. Moreover, we have also disclosed charge-transfer complex (CTC) formation between thiolate and acrylate/styrene to realize the visible-light-driven hydrocarboxylation of alkenes with CO2 via generation of a CO2 or alkene radical anion. On the basis of this novel CTC, the visible-light-driven organocatalytic hydrocarboxylation of alkenes with CO2 has also been realized using a Hantzsch ester as an effective reductant.

Probing the Ag – liquid gallium system and its interaction with redox active solutions for catalysis and AgTCNQ formation

The creation of liquid metal alloys that are reacted with species in solution is a relatively new approach to the synthesis of functional nanomaterials. In this work we explore the liquid Ag–Ga system and its interaction with redox active species in aqueous solution in the areas of heterogeneous catalysis and charge transfer complex formation. It was found that when Ag is alloyed with Ga that solid microwires of Ag2Ga were formed over time with a width of ca. 1–1.5 µm of up to 160 µm in length. This Ga/Ag2Ga composite was then investigated for the discolouration of methylene blue dye in both the liquid and solid state where little difference in activity was found resulting in 40% discolouration after 30 min. However, if nitrogen gas was passed through the liquid form of the catalyst the conversion efficiency of the catalyst increased significantly up to 99% after 1 min and could be re-used for up to 10 cycles. In addition, the catalytic conversion of 4-nitrophenol to 4-aminophenol at the liquid Ga/Ag2Ga catalyst was significantly greater than liquid Ga and could be reused for up to 5 cycles. The interaction of liquid Ag–Ga with the well-known electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) was also studied where it was found that a reaction only occurred immediately after mixing Ag microparticles with liquid Ga and before any Ag2Ga microwires were formed. The reaction conditions of bubbling nitrogen gas through the liquid Ag–Ga catalysts in an acetonitrile solution of TCNQ resulted in the time dependent formation of various morphologies of the semi-conducting charge transfer complex AgTCNQ. This work shows that alloying metals with Ga can result in the time dependent formation of a variety of materials under different reaction conditions when exposed to solution based redox active species.

Charge-transfer (CT) dynamics of triamterene with 2,3-dichloro-5,6-dicyano-p-benzoquinone acceptor: A n → π* model CT complex generated by liquid- and solid-state reactions

Since it was first described in 1969 by Robert Mulliken, the charge-transfer (CT) chemical reaction has received unparalleled attention and inspired extensive research efforts. This is because CT yields new charge-transfer complexes (CTCs) with unique physical, biological, and chemical characteristics that render them beneficial to academia, material science, medicine, and pharmacology. The formation of CTCs by the liquid-state reaction is described well in literature, while their formation by the solid-state reaction is less well studied. For this reason, we conducted a series of works to reveal the formation of CTCs by solid-state reaction between the donor and acceptor. This work represents a model CT complex generated by liquid- and solid-state reactions between a typical donor (triamterene) and a typical acceptor (2,3-dichloro-5,6-dicyano-p-benzoquinone; DDQ). Outcomes in this work indicate that both reaction types (liquid- and solid-state) yielded the same CT complex between the investigated donor and acceptor molecules, which were bridged by a n → π* transition.

Donor-acceptor complex formation in tetra-n-butylammonium chloride: n-decanoic acid deep eutectic solvent.

Complex formation between pyrene (Py) and N,N-dimethylaniline (DMA) is presented in a deep eutectic solvent constituting of tetra-n-butylammonium chloride (TBAC) and n-decanoic acid (DA) in a 1:2 mol ratio, respectively, named TBAC:DA. The addition of DMA to a Py solution of TBAC:DA results in the formation of a fluorescent Py-DMA charge-transfer complex, which is manifested via a broad structureless bathochromically shifted band centered at 550(±2) nm. The solvatochromic nature of the Py-DMA fluorescent complex indicates the solvent polarity of TBAC:DA to be higher than that of methanol. The absence of a negative pre-exponential factor in the intensity decay at 550 nm combined with the excitation scans implies the presence of weak interaction between Py and DMA in the ground-state, leading to the rapid formation of a Py-DMA complex possibly at a sub-nanosecond time scale. The Stern-Volmer quenching constant (KSV) varies from 53(±2) to 96(±1) M-1, and the bimolecular quenching rate constant (kq) varies from 3.0(±0.4) × 108 to 8.8(±1.3) × 108 M-1 s-1 by increasing the temperature (T) from 283.15 to 313.15 K, implying efficient deactivation of electron-acceptor Py in the excited-state induced effectively by the electron-donor DMA within TBAC:DA. ln kq varies linearly with 1/T with an activation energy (Ea) of 26.4(±0.4) kJ mol-1. The linear behavior between kq and 1/η suggests conformity to the Stokes-Einstein relationship within TBAC:DA. The Py-DMA complex formation efficiency increases with an increase in T and reaches maxima at 298.15 K before decreasing with a further increase in T. The initial reduction in η favors Py-DMA complex formation; this effect is overcome by preferential thermal deactivation of the Py-DMA fluorescent complex as compared to that of pyrene.

Chromic and Fluorescence-Responsive Metal-Organic Frameworks Afforded by N-Amination Modification.

Sensory materials that show color and/or fluorescence changes in response to specific gases or vapors have important applications in many fields. Here, we report the postsynthetic preparation of novel sensory metal-organic frameworks (MOFs) and their multiple responsive properties. Through postsynthetic N-amination, the 2,2'-bipyridyl spacers in a Zr(IV) MOF are partially transformed into N-aminobipyridinium. The new MOF (Zr-bpy-A) shows chromic behavior toward ammonia and amines because the electron-deficient pyridinium groups form charge-transfer complexes with amino moieties. It also shows a unique chromic response to formaldehyde owing to the Schiff-base condensation with the N-amino groups. Furthermore, the N-amino group can be used to graft different polycyclic aromatic hydrocarbons, which endow the MOF with strong fluorescence of variable colors and afford a high-contrast fluorescence response to ammonia/amines and formaldehyde associated with the chromic response. The presence of the unquaternized bipyridyl group also leads to a fluorescence response to HCl. The multiple responsive behaviors hold appeal for applications in sensing, switching, and antifake marking, which are illustrated with a test paper and writing ink.

A New Charge Transfer Reaction for Spectrophotometric Determination of Nitrazepam Using Reverse Flow Injection Analysis

A new sensitive spectrophotometric method conjugated with reverse flow-injection analysis has been developed for the assay of nitrazepam (NZP) in the bulk drug and dosage form. The proposed method is based on the formation of charge-transfer complex between reduced NZP (donor) with a new reagent (acceptor) namely, 4,4'-tetramethyl-diaminodiphenyl-methane in the presence of NaIO4 as an oxidant. A violet-colored product was quantified spectrophotometrically at 560 nm. All the chemical and physical conditions of the reaction have been studied carefully. Under the selected optimum conditions, Beer’s law was obeyed in the concentration range of 5–300 µg/mL. The limits of detection and quantification were 5 and 16 µg/mL, respectively, with a sampling frequency of 62 sample/h. The proposed method was further successfully applied for the assay of NZP in commercial dosage forms and compared statistically with the reference method using t- and F-tests. The method was characterized by its accuracy and simplicity.

Biomass-Derived Humin-like Furanic Polymers as an Effective UV-Shielding Agent for Optically Transparent Thin-Film Composites

Synthesis of 5-hydroxymethylfurfural from saccharide biomass yields humin-like furanic polymers (BFPs) as a byproduct. As a maiden attempt, BFP was successfully separated and explored as an effective UV-shielding agent by blending with poly(vinyl alcohol) (PVA, 0.5–2.0 wt %). PVA/BFP composite films showed high stability and durability even under extreme conditions, such as intense UV irradiation, sunlight exposure, and thermal treatment, while retaining their UV-shielding efficiency. The PVA/BFP (0.5–2.0 wt %) composite film showed 63–99% UV-shielding capacity in the entire UV range with 48–89% optical transparency; in addition, the decolorized BFP composite film showed superior UV-shielding efficiency (98%) with >98% optical transparency. Thermal stability of the film witnessed significant improvement, exhibiting higher thermal degradation temperature (Td, by 57 °C) and glass transition temperature (by 7.3 °C). Further, the composite film exhibited an excellent mechanical strength of 71 MPa and 338% strain to break, compared to the PVA film (25 MPa mechanical strength and 177% strain), along with enhanced DMA storage modulus. Application of UV shielding was demonstrated through rhodamine B photodegradationstability, which showed that incorporation of BFP resulted in mere 0.4% degradation of rhodamine B, while neat PVA films showed 100% degradation. The enhanced photostability of rhodamine B while using PVA/BFP is attributed to the formation of BFP and PVA charge-transfer complexes.

Charge generation efficiency of electrically doped organic semiconductors

Organic semiconductors (OSCs) have been a significant focus of research for electronic devices over the years exclusively due to their superior mechanical and optical properties as opposed to conventional inorganic semiconductors (ISCs) such as silicon or germanium. These unique materials have smoothened the path for developing extremely light-weight and ultrathin electronic devices with built-in flexibility and transparency for a considerably low cost. However, the commercial application of these organic materials is limited by their inferior electrical conductivity and charge carrier mobility compared with inorganic counterparts. This review article presents an overview of the works published on how to control and adjust the electrical conductivity of OSCs, focusing on electrical doping. The main point of this review is related to the principles and fundamental mechanisms of charge generation efficiency (CGE) in OSCs, which are significantly different from those of ISCs. The reported CGE of OSCs, defined as the ratio of the generated charge carriers to the dopants, is found to be in the range of a few percent and is significantly small compared with the ISCs. The origin of this lies in the lower dissociation rate of the charge transfer complexes (CTCs) formed between the tightly bound ionized dopants and generated charges. The CTCs induce localized electron-hole pairs, and the dissociation of such CTCs into free charge carriers requires large activation energies to overcome the strong Coulombic forces exerted on the generated charges by the dopant ions. Therefore, high doping concentrations are required to generate a large number of free charge carriers in doped OSC films. In this review, the CGE of OSCs is discussed in detail from the point of view of CTC formation and charge separation efficiencies.

Controlling the Formation of Charge Transfer Complexes in Chemically Doped Semiconducting Polymers

Chemical doping of semiconducting polymers predominantly takes place via integer charge transfer (ICT), where an electron is entirely removed from the host conjugated polymer and transferred to res...

Gliclazide charge transfer complexes with some benzoquinone acceptors: Synthesis, structural characterization, thermal analyses, DFT studies, evaluation of anticancer activity and utility for determination of gliclazide in pure and dosage forms

The reaction between gliclazide (GLZ, the antidiabetic drug) as n-electron donor with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, PCA) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as π-acceptors led to the formation of 1:1 charge-transfer (CT) complexes as the final products. These reactions were utilized for the spectrophotometric quantitative determination of GLZ in its pure and pharmaceutical forms (diamicron and diamedizen tablets) under various optimized conditions and a good linearity was obtained with a wide range of concentrations of 10-450 and 30-500 µg mL−1 using DDQ and PCA reagents, respectively. The limits of detection and quantification, inter-day and intra-day accuracy and precision were optimized. The formed complexes were structurally characterized using different spectral methods. Theoretical DFT/TD-DFT calculations were performed to investigate their optimized geometries, molecular electrostatic potentials (MESP), quantum chemical parameters and electronic spectra. Thermal properties of the formed CT complexes were studied and their anticancer activity were screened against breast cancer MCF-7 cell line.