Number Of Electron Donors Research Articles

Electron donor–acceptor type delayed fluorescence emitters with inverted singlet and triplet excited states

Emitters having a negative energy difference between their lowest singlet and triplet excited states are promising candidates for developing next-generation organic light-emitting diodes (OLEDs) because their inverted singlet and triplet (IST) excited states enable exothermic reverse intersystem crossing, which results in a fast rate constant for reverse intersystem crossing and facilitates the efficient harvesting of triplet excitons. This study reports the development of organic emitters comprising 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene as an electron acceptor and 10H-spiro[acridine-9,9′-fluorene] as an electron donor that exhibit IST-excited states. We confirmed the presence of IST excited states in our emitters using photoluminescence spectroscopy, time-correlated single-photon counting, and excited-state density functional theory calculations. In addition, by varying the number of electron donors and the dihedral angles between the electron donor and acceptor, we identified the underlying reasons for the inversion of the singlet and triplet states. Furthermore, we achieved high external quantum efficiencies of up to 30 % by utilizing the IST emitters as emitting layers in OLEDs.

Lewis Structures and the Bonding Classification of End-on Bridging Dinitrogen Transition Metal Complexes.

The activation of dinitrogen by coordination to transition metal ions is a widely used and promising approach to the utilization of Earth's most abundant nitrogen source for chemical synthesis. End-on bridging N2 complexes (μ-η1:η1-N2) are key species in nitrogen fixation chemistry, but a lack of consensus on the seemingly simple task of assigning a Lewis structure for such complexes has prevented application of valence electron counting and other tools for understanding and predicting reactivity trends. The Lewis structures of bridging N2 complexes have traditionally been determined by comparing the experimentally observed NN distance to the bond lengths of free N2, diazene, and hydrazine. We introduce an alternative approach here and argue that the Lewis structure should be assigned based on the total π-bond order in the MNNM core (number of π-bonds), which derives from the character (bonding or antibonding) and occupancy of the delocalized π-symmetry molecular orbitals (π-MOs) in MNNM. To illustrate this approach, the complexes cis,cis-[(iPr4PONOP)MCl2]2(μ-N2) (M = W, Re, and Os) are examined in detail. Each complex is shown to have a different number of nitrogen-nitrogen and metal-nitrogen π-bonds, indicated as, respectively: W≡N-N≡W, Re═N═N═Re, and Os-N≡N-Os. It follows that each of these Lewis structures represents a distinct class of complexes (diazanyl, diazenyl, and dinitrogen, respectively), in which the μ-N2 ligand has a different electron donor number (total of 8e-, 6e-, or 4e-, respectively). We show how this classification can greatly aid in understanding and predicting the properties and reactivity patterns of μ-N2 complexes.

A simple molecular design towards the conversion of a MCL backbone to a multifunctional emitter exhibiting polymorphism, AIE, TADF and MCL

Compared with the large number of single-function materials such as aggregation-induced emission (AIE), mechanochromic luminescence (MCL), or thermally activated delayed fluorescence (TADF) emitters, multifunctional emitting materials offer more opportunities in practical applications. In this report, we provide a simple molecular design strategy towards the conversion of a MCL building block to a multifunctional emitter. Through altering the substituent sites and increasing the number of electron donors and steric hindrance on a normal MCL backbone benzo[d,e]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one, a novel multifunctional material 10,11-bis-(4-diphenylamino-phenyl)-benzo[d,e]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (10,11-2TPA-BBI) is designed and synthesized. 10,11-2TPA-BBI exhibits simultaneous polymorphism, AIE, MCL and TADF properties. It can form four different aggregate species: yellow solid (YS) and orange solid (OS), orange flake-shaped crystal (OC), and red prism-like crystal (RC). Among them, because of the small energy gaps (ΔESTs < 0.3 eV) between the singlet and triplet excited states, OS, OC and RC exhibit TADF properties, while YS show normal fluorescence characteristics with a large ΔEST of 0.33 eV. OS can be reversibly transformed into YS upon external stimuli, which can be attributed to the emission switch between local excited state and charge transfer state. Crystallographic study indicates that the bulky structure and weak intermolecular interactions account for polymorphism and AIE properties. This work will provide a simple molecular design strategy for multifunctional materials.

Chromatographic study of electron acceptor–donor properties of 4-(trans-4’-n-alkylcyclohexyl) benzoates

A new approach of characterizing the specific properties of 4-(trans-4’-n-alkylcyclohexyl) benzoates, based on the interaction of the acidic and basic testing substances, for their form Crystalline, Smectic B and Nematic have been proposed. The testing substances selected for our study have been considered in the light of the results obtained in the previous research and the data available in the literature for other liquid crystals with different structures. The DN values denoting the electron donor number in the Gutmann scale and the AN* values indicating the acceptor number in the Riddle-Fowkes scale have been chosen in the estimation of the electron acceptor parameter KA and electron donor parameter KD values. The temperature-dependent quotients of KA to KD are employed for the assessment of the electron donor-acceptor properties of 4-(trans-4’-n-alkylcyclohexyl) benzoates. The 4-(trans-4’-n-alkyl cyclohexyl) benzoates tested have the affinity to act as a donor of electrons concerning electron acceptor of the testing substance. The sizes and shapes effects of the testing substances (or penetrants) and the LCs tested (or solvents while in mesophases) are taken into account. The inverse gas chromatography tests were supported by the Quantitative Structure-Activity Relationship modelling technique to determine which part (or group) of liquid crystals tested was dominant in the interaction with the testing substances.

Nucleic acid-functionalized metal-organic framework for ultrasensitive immobilization-free photoelectrochemical biosensing

This work established an immobilization-free photoelectrochemical (PEC) biosensor for ultrasensitive determination of carcinoembryonic antigen (CEA) based on the DNA-functionalized metal-organic frameworks (MOFs) and T7 exonuclease-aided recycling amplification. In this proposal, MOFs were served as nanocarriers for efficient encapsulation of electron donors, while an ingeniously designed hairpin probe (HP) employed as the recognition element. The recognition of CEA by its aptamer sequence in HP triggered the conformational change and the T7 exonuclease-aided recycling amplification, which opened the pore of MOFs to release a large number of electron donors, producing a significantly increased photocurrent. Benefitting from the high loading ability of MOFs and the excellent amplification efficiency of the T7 exonuclease-assisted recycling process, the proposed biosensor is capable of ultrasensitive and highly selective determination of CEA with a detection limit down to 0.36 fg mL-1 and a wide linear range from 1.0 fg mL-1 to 10 ng mL-1. Moreover, the proposed biosensor can also apply to measure CEA in spiked serum samples, indicating that this PEC biosensor holds excellent potential for application in bioanalysis and early disease diagnosis.

The electron transfer mechanism between metal and amorphous polymers in humidity environment for triboelectric nanogenerator

Humidity tends to deteriorate the output performance and the stability of triboelectric nanogenerator (TENG). However, the microscopic mechanism of how water molecules adsorbed on the surface affect electron transfer in the metal-amorphous polymer contact electrification of TENG remains elusive. Here in order to investigate the effect of humidity on the electron transfer process between metal-amorphous polymer in TENG, we employ first-principles calculations to study the typical material pair Al- polyethylene (PE). We find that water molecules adsorbed between the interfaces replace the original electron donor Al in the electron transfer between Al/PE pair, providing the electron to the LUMO (lowest unoccupied molecular orbital) of PE and the surface atoms of Al and reducing the amount of charge transfer for Al/PE pair. Most importantly, we demonstrate that the existence of hydrogen bonds makes water molecules the electron donor (positively charged) in metal/polymer interface, in which only the non-hydrogen bond H atom is the main electron donor. In addition, it is also found that the number of transferred charge is closely related to the number of electron donors, which can explain the declining trend of the amount of charge transfer. The gained insights provide a theoretical basis for the regulation of the contact electrification process and the design of TENG in humidity environment.

Influence of the structure of ceftazidime on obtaining biologically active cellulosic bandage

Biologically active fibers as drug carriers have improved characteristics in comparison with conventional medical therapies. Cellulosic fibers as hydrophilic and biocompatible, nontoxic and eco-friendly make a good polymer matrix for obtaining biologically active fibers. Current investigations in this area show that the features of these fibers depend on the type of carrier as well as the drug structure. Loading drugs on the fiber carrier is accomplished by ionic bonding between ionized drugs and the groups fixed on the fiber (by ion exchange) or loosely adsorption on the fiber through hydrophobic interactions. These interactions can be achieved between hydrophobic parts of the drug and the fiber carrier or among the hydrophobic drugs bonded on the fiber. Prevailing mechanism of ionized drug bonding on the carrier is ionic, although different hydrophobic interactions can contribute the drug loading to varying degrees. In this paper oxidized cellulose (OC) with different carboxylic group content is obtained by selective oxidation and used for chemical bonding of antibiotic ceftazidime. In its structure this antibiotic has aminothiazole ring and pyridine ring in the side chains of cephem nucleus. Ceftazidime has two carboxylic groups and also great number of electron donors and acceptors. Due to these groups and structures ceftazidime is able to form multiple chemical bonds i. e. interactions with oxidized cellulosic bandage. The bonding was performed in antibiotic water solution concentration of c=3,4?10-3 mol/L at room temperature (22 ? 1?C), while desorption was performed in physiological solution. The amounts of bonded and released antibiotic were determined spectrophotometrically in UV range. Maximum amount of bound drug (0,0243 mg/g) was obtained during the sorption on the oxidized bandage with 2,276 mmol/g COOH and the maximum amount of released drug was 0,0238 mmol/g. Antimicrobial activity of the samples with bonded ceftazidime was tested in vitro against Staphylococcus aureus, Bacillus subtilis i Escherichia coli by agar diffusion test. The bigest zone of inhibition was obtained for Escherichia. The paper studies the influence of ceftazidime chemical structure, pH of solution in which sorption is performed and sorption duration, on the amount of bonded drug. It was established that the drug bonding was achieved by ionic bonds and the hydrogen bonds of the drug functional groups with oxidised cellulose bandage. Also it was found that buffering of the drug solution, in which bonding is performed, can increase the amount of ceftazidime bonded on the fiber.

Thermal and spectroscopic characterization of zinc(II) bis(dipyrrinate)s crystal solvates with acetone, dimethyl sulfoxide, and triethylamine

The crystal solvates of 2,2′-, 2,3′- and 3,3′-bis(dipyrrinato)zinc(II) with acetone, dimethyl sulfoxide, and triethylamine were obtained by slow crystallization. Composition, stability, and spectral luminescent properties of the samples were studied. Spectroscopic studies showed that the quantum yield (φ) of crystal solvates in cyclohexane is noticeably lower (to ~1.5–4.5 times) than φ for of [Zn2 L 2] helicates. The thermal dissociation processes of crystal solvates in an argon atmosphere have been investigated. It is shown that bis(dipyrrinato)zinc(II) form stable supramolecular complexes with electron donor molecules X of the composition [Zn2 L 2Xn], where n = 1, 2, or 4. Crystal solvates are stable up to a temperature ~356.9–412.2 К. The energy stability of the solvates [Zn2 L 2Xn] reduced at replacing the 2,2′-bis(dipyrrine) on 2,3′- and 3,3′-isomer and with a decrease in electron donor number of molecular ligands X: Acet, DMSO, TEA. It is demonstrated that the high energies of the coordination interactions Zn–X in supramolecular complexes [Zn2 L 2Xn] are the main cause of the fluorescence quenching of [Zn2 L 2] luminophores in the presence of electron donor ligands X. The obtained results are of interest for the development on the basis of [Zn2 L 2] of the new fluorescent sensors of the electron donor molecules.

Application of DSC to study the promoting effect of a small amount of high donor number solvent on the solvent swelling of kerogen with non-covalent cross-links in non-polar solvents

This paper investigates the effect of a small amount of a strong electron-donating solvent (or high electron donor number solvent) on the solvent swelling of covalently and non-covalently cross-linked Kukersite oil shale kerogen in non-polar solvents. The non-polar (or non-specifically interacting) solvents used in the study were benzene, o-xylene and tetralin. The specifically interacting (or swelling promoting), high donor number solvent added was N-methyl-2-pyrrolidinone (NMP). The changes in solvent uptake of the samples caused by the specifically interacting solvent, previously in equilibrium with respect to a non-specifically interacting solvent, were studied using a Differential Scanning Calorimeter (DSC). The specifically interacting solvent was added in small amounts, up to roughly 2mmol of NMP per gram of kerogen (that is, 0.208, 0.416, 0.624, 0.831, 1.039 and 2.07mmol of NMP per gram of kerogen). The experiments indicated an increase up to about two times in the swelling ratio by adding a strong electron donor solvent at 0.8mmol per gram of kerogen. The effect was most pronounced in the case of tetralin, the solvent with the lowest initial swelling ratio and the largest molar volume. From solvent melting point depression and gas chromatography (GC) experiments, it could be stated that up to 0.8mmolNMP/gkerogen most of the high electron donor solvent was absorbed by the Kukersite kerogen. The value 0.8mmol NMP per gram of kerogen is specific to Kukersite oil shale kerogen. The DSC-based method applied can be considered quantitative up to this limiting value of 0.8mmol NMP per gram of kerogen, and above this value the results indicate characteristic trends.

Kukersite oil shale kerogen solvent swelling in binary mixtures

This work presents experimental data on volumetric swelling of Estonian kukersite oil shale kerogen in 11 different binary mixtures, prepared using nine different solvents. Variations in equilibrium swelling ratios have been studied as a function of mixture composition. The results confirm the important role of specific interactions in determining the swelling behavior of this kerogen. Swelling of kukersite kerogen in mixtures with high electron donor number solvents (such as pyridine, propylamine, and NMP) show the highest values of equilibrium swelling ratios over the very broad solubility parameter range. In terms of maximizing swelling of this kerogen, binary solvent mixtures do not offer particular advantage relative to pure, strong electron donor solvents.

Charging of unfunctionalized graphene in organic solvents

Unfunctionalized graphene is positively or negatively charged when it is dispersed in organic solvents. The charging is negative in solvents with high electron donor numbers and positive in those with low donor numbers. We suggest that the charging originates from electron transfer between graphene surfaces and solvent molecules, and the stable dispersion of unfunctionalized graphene in organic solvents is mainly controlled by electrostatic repulsion between the charged graphene surfaces.

SOLVENT SWELLING OF DICTYONEMA OIL SHALE

The present work investigates volumetric swelling of Estonian Dictyonema oil shale, as a representative of black shales of the Baltoscandian basin, in 22 solvents. This study shows that kerogen of Dictyonema oil shale is characterized by a low degree of swelling indicating a highly cross-linked structure. The relatively high swellability in high Guttmann’s electron donor number solvents indicates the importance of non-covalent cross-links, such as hydrogen bonding, in swelling process and raises concern regarding the use of regular solution-based approaches. Despite this, the solubility parameter, a fundamental thermodynamic property, was tentatively determined from swelling data.

Electronic spectra of uranium tetrachloride clusters with electron-donor ligands

Electronic absorption spectra of nanoclusters of uranium tetrachloride are obtained experimentally and analyzed over a wide spectral range, from the visible to the IR. The structure of the long wavelength electronic absorption spectra is discussed in terms of the structure and electron-donor number of the attached ligand. Molecules of dimethyl sulfoxide (DMSO), hexamethyl phosphotriamide (HMPT), and water were used as ligands. The effect of the symmetry of the surroundings of the U4+ ion on the structure of the electronic spectrum is examined.

Photoinduced multi-electron transfer in the Dn–A system consisting of multi-phthalocyanines linked to one carbon nanotube

A Dn-A model in which a carbon nanotube (nanoscaled electron acceptor A) is attached with a number of electron donors (Dn), i.e. amino phthalocyanines, was employed to reveal the different nature of photoinduced electron transfer (PeT) in the nanoscaled model from that of a usual one-to-one linked D-A system, which is known to form the single-charge separation state D*+-A*-via well-studied single-electron transfer. For the Dn-A system, however, a one-step multi-electron transfer from multi donors to the same acceptor occurs simultaneously to generate a long-lived multiple-charge separation state Dn*+-A*n- (n>1), which is desirable for efficiently mimicking PSII in photosynthesis.

Cytochrome b5, Not Superoxide Anion Radical, Is a Major Reductant of Indoleamine 2,3-Dioxygenase in Human Cells

The heme protein indoleamine 2,3-dioxygenase (IDO) initiates oxidative metabolism of tryptophan along the kynurenine pathway, and this requires reductive activation of Fe(3+)-IDO. The current dogma is that superoxide anion radical (O(2)(*-)) is responsible for this activation, based largely on previous work employing purified rabbit IDO and rabbit enterocytes. We have re-investigated this role of O(2)(*-) using purified recombinant human IDO (rhIDO), rabbit enterocytes that constitutively express IDO, human endothelial cells, and monocyte-derived macrophages treated with interferon-gamma to induce IDO expression, and two cell lines transfected with the human IDO gene. Both potassium superoxide and O(2)(*-) generated by xanthine oxidase modestly activated rhIDO, in reactions that were prevented completely by superoxide dismutase (SOD). In contrast, SOD mimetics had no effect on IDO activity in enterocytes and interferon-gamma-treated human cells, despite significantly decreasing cellular O(2)(*-) Similarly, cellular IDO activity was unaffected by increasing SOD activity via co-expression of Cu,Zn-SOD or by increasing cellular O(2)(*-) via treatment of cells with menadione. Other reductants, such as tetrahydrobiopterin, ascorbate, and cytochrome P450 reductase, were ineffective in activating cellular IDO. However, recombinant human cytochrome b(5) plus cytochrome P450 reductase and NADPH reduced Fe(3+)-IDO to Fe(2+)-IDO and activated rhIDO in a reconstituted system, a reaction inhibited marginally by SOD. Additionally, short interfering RNA-mediated knockdown of microsomal cytochrome b(5) significantly decreased IDO activity in IDO-transfected cells. Together, our data show that cytochrome b(5) rather than O(2)(*-) plays a major role in the activation of IDO in human cells.

Cytochromes c of Acidithiobacillus ferrooxidans.

The chemolithoautotrophic Gram-negative bacterium Acidithiobacillus ferrooxidans is versatile and can grow on a number of electron donors and acceptors. In the A. ferrooxidans ATCC 23270 genome, computer analysis identified 11 genes encoding putative cytochromes c. At least eight putative cytochromes c were differentiated on gels in ATCC 33020 cells grown on ferrous iron or sulfur. All these cytochromes were associated with the inner or the outer membranes. Lower levels of total cytochromes c were observed in sulfur- than in ferrous iron-grown cells. One cytochrome c was specific for sulfur conditions while three were specific for iron conditions, suggesting that cytochrome c synthesis is modulated depending on the electron donor.

Cytochromes c of Acidithiobacillus ferrooxidans

The chemolithoautotrophic Gram-negative bacterium Acidithiobacillus ferrooxidans is versatile and can grow on a number of electron donors and acceptors. In the A. ferrooxidans ATCC 23270 genome, computer analysis identified 11 genes encoding putative cytochromes c. At least eight putative cytochromes c were differentiated on gels in ATCC 33020 cells grown on ferrous iron or sulfur. All these cytochromes were associated with the inner or the outer membranes. Lower levels of total cytochromes c were observed in sulfur- than in ferrous iron-grown cells. One cytochrome c was specific for sulfur conditions while three were specific for iron conditions, suggesting that cytochrome c synthesis is modulated depending on the electron donor.

Determination of the Photoinduced Electron Transfer Rate Constant in Langmuir−Blodgett Films by Time-Resolved Fluorescence

The feasibility of a relevant analysis of the fluorescence decays of Langmuir−Blodgett−Kuhn films where electron and energy transfer occur simultaneously is demonstrated. Starting from a stretched exponential, describing Forster-type energy transfer, a model describing simultaneous photoinduced electron transfer and energy transfer is developed. In this model a binomial distribution of electron donors (pyrene) is assumed in the layer adjacent to the excited probe (Rhodamine G). When the fluorescence decays of two or three samples with different concentrations of electron donors are analyzed simultaneously with the decay of a sample containing no electron donor, reliable values of the global parameters (the fluorescence decay time of the unquenched probe, the rate constant for electron transfer, and the rate constant for energy transfer to a trap) could be obtained. The local parameters (the average number of electron donors in a site opposite the probe and the fraction of the monolayer containing an elect...

98/02683 Low temperature extractability and solvent swelling of Turkish lignites: Onal, Y. and Ceylan, K. Fuel Process. Technol., 1997, 53, (1/2), 81–97.

Six Turkish lignites have been pretreated with the solutions of HCl or sodium ethanolate at room temperature or at 150°C. The volumetric swelling of the raw or pretreated lignites have been investigated by using 13 solvents at room temperature. These lignites have been subjected to Soxhlet extractions in the same solvents and in the linear alkylamines. The solubility of the samples in toluene under supercritical conditions were also tested. The effect of solvent on swelling ratio and on the extraction yields of the raw or pretreated lignites have been examined. The results have indicated that both swelling and extraction yields generally increased after the pretreatments and the increments are higher with hydrogen bonding solvents. Especially, sodium ethanolate pretreatment increases the solubility in toluene under supercritical conditions. The results suggest that solvent solubility parameter and electron donor number are effective in both swelling and solubility. A qualitative information regarding the structural characteristics of extracts was obtained by UV and NMR analysis.

METABOLIC PROPERTIES OF DENITRIFYING BACTERIA ADAPTING TO METHANOL AND ETHANOL IN ACTIVATED SLUDGE

The effect of external carbon sources on metabolic properties of the denitrifying community in single-sludge systems with predenitrification was investigated. Sludge samples were collected from full-scale and pilot-scale experimental lines during microbial adaption to methanol and ethanol, respectively. Changes in functional properties were studied by measuring denitrification capacity with different electron donors in batch tests using the acetylene inhibition technique. Substrate-use profiles were analysed with principal component analysis. Adaptation to methanol was slow, and the capacity to denitrify with acetate decreased continuously. Short-chain fatty acids were less popular for denitrifiers in the methanol-adapted sludge than they were in the reference sludge, while the capacity to denitrify with methanol and ethanol was higher. Denitrification capacity with ethanol and acetate in the ethanol adapting sludge increased rapidly. The ethanol-adapted sludge also had a higher capacity to denitrify with butyrate, glycerol, and methanol. Neither methanol nor ethanol as external carbon affected denitrification capacity with aromatic compounds or glucose. A reduced ability to denitrify with a vast number of electron donors can be regarded as a negative characteristic, since it reflects a lower capacity to make use of substances in the sewage. © 1998 Elsevier Science Ltd. All rights reserved