Electron-donor Electron-acceptor Research Articles

Thiophene or Pyridine-Substituted Quinoline Derivatives: Synthesis, Properties, and Electropolymerization for Energy Storage

Designing novel electropolymerizable monomers is essential in developing electron donor-electron acceptor (D-A) type conjugated polymers for applications in sensing, catalysis, and energy storage. Thiophene and pyridine-substituted quinoline-based molecules (Th-Q, DTh-Q, and Py-Q) are synthesized in this work, and their crystal structures, optical properties, and electrochemical properties are investigated. The potentiostatic electropolymerization of these molecules are successfully carried out on carbon cloth substrate, with the thiophene and quinoline as the possible electropolymerizable units. The PTh-Q shows the best charge storage performance ( 1.12 × 10 − 3 C at 0.02 mA cm-2 in the potential range of 0-1 V) in 0.1 M Na2SO4, and maintains 77% of the initial capacity after 3000 charge-discharge cycles at 0.02 mA cm-2. The morphology and structure of the PTh-Q does not alter significantly after the repetitive charge-discharge cycling. The superior charge storage performance of the PTh-Q than PDTh-Q and PPy-Q is originated from the exposed highest amount of electrochemically active sites and the participation of redox processes of both hydroxyl/ketone structures on quinoline and thiophene groups.

Phthalocyanine zirconium diazo passivation of black phosphorus for efficient smoke suppression, flame retardant and mechanical enhancement

The existence of lone pair electrons on the surface of black phosphorus (BP) is a good electron acceptor, which has good structural stability when it forms new electron donor-electron acceptor pairs when combined with electron donators such as phthalocyanine. In order to bond functional groups available for reaction on the surface of BP, the lamellae group density was increased by functionalizing BP with benzoic acid diazonium salt, and then the carboxylated BP was covalently grafted with phthalocyanine zirconium, and finally the phthalocyanine-zirconium polyphosphazene functionalized BP (BP-ZrPZN) was obtained by crosslinking reaction. Subsequently, BP-ZrPZN was added into the EP matrix as nano filler to form the reinforced system. The results showed that the thermal stability and fire safety of EP composites containing 2 wt% BP-ZrPZN were significantly improved. The peak heat release rate and total heat release rate were reduced by 56.8 % and 54.1 %, respectively, and the limited oxygen index was up to 33 % and UL94 value was V-0. In addition, the presence of BP-ZrPZN greatly improved the ability of BP to inhibit toxic smoke. The total smoke yield of EP composites decreased by 62.7 %. The tensile strength and impact strength increased by 36.1 % and 50.6 % respectively. Therefore, the functional strategy of phthalocyanine in this work will provide a reasonable and feasible way to optimize the flame retardancy and smoke suppression effect of BP.

A correlation between electron-hole pair radii and magnetomodulation of exciplex fluorescence in electron donor-electron acceptor organic systems

Electric field dependencies of electromodulated photoluminescence and magnitudes of the magnetic-field effect on photoluminescence have been measured in vacuum-evaporated films of m-MTDATA [4,4′,4″-tris(N-(3-methylphenyl)-N-phenylamino)triphenylamine]:bathophenanthroline, m-MTDATA:BCP (bathocuproine), as well as 4,4′,4″-tris[2-naphthyl(phenyl)amino]triphenylamine:BCP. The Sano-Tachiya-Noolandi-Hong extension of standard Onsager formalism was used to investigate the electron-hole pair dissociation process which allowed us to estimate the pair intercarrier distances and the final speed of carrier recombination. A distinct correlation between the pair radii and the magnitude of the magnetic-field effect has been found.

Amine-functionalized MIL-53(Al)-coated stainless steel fiber for efficient solid-phase microextraction of synthetic musks and organochlorine pesticides in water samples.

The fiber coating is the key part of the solid-phase microextraction (SPME) technique, and it determines the sensitivity, selectivity, and repeatability of the analytical method. In this work, amine (NH2)-functionalized material of Institute Lavoisier (MIL)-53(Al) nanoparticles were successfully synthesized, characterized, and applied as the SPME fiber coating for efficient sample pretreatment owing to their unique structures and excellent adsorption properties. Under optimized conditions, the NH2-MIL-53(Al)-coated fiber showed good precision, low limits of detection (LODs) [0.025-0.83ngL-1 for synthetic musks (SMs) and 0.051-0.97ngL-1 for organochlorine pesticides (OCPs)], and good linearity. Experimental results showed that the NH2-MIL-53(Al) SPME coating was solvent resistant and thermostable. In addition, the extraction efficiencies of the NH2-MIL-53(Al) coating for SMs and OCPs were higher than those of commercially available SPME fiber coatings such as polydimethylsiloxane, polydimethylsiloxane-divinylbenzene, and polyacrylate. The reasons may be that the analytes are adsorbed on NH2-MIL-53(Al) primarily through π-π interactions, electron donor-electron acceptor interactions, and hydrogen bonds between the analytes and organic linkers of the material. Direct immersion (DI) SPME-gas chromatography-mass spectrometry methods based on NH2-MIL-53(Al) were successfully applied for the analysis of tap and river water samples. The recoveries were 80.3-115% for SMs and 77.4-117% for OCPs. These results indicate that the NH2-MIL-53(Al) coating may be a promising alternative to SPME coatings for the enrichment of SMs and OCPs.

Study of marine bacteria adhesion on sea-immersed 304 and 316 stainless steels: experimental and theoretical investigations

In this study, we investigated the potential adhesion of marine bacteria isolated from seawater in the port of Chmaâla, Morocco, to sea-immersed 304 and 316 stainless steels using thermodynamic approach and the Environmental Scanning Electron Microscopy (ESEM). Furthermore, the physicochemical properties including hydrophobicity and electron donor / electron acceptor (Lewis acid-base) of bacterial isolates and both substrates were evaluated using the contact angle measurements. The molecular identification indicated that the isolated strains were Bacillus thuringiensis and Bacillus amyloliquefascience. Results also showed that both bacterial strains’s cells have a hydrophilic character with ΔGiwi values of 29.30 and 24.12 mJ m−2 respectively for Bacillus thuringiensis and Bacillus amyloliquefascience, and are strong electron donating (γ−) and weakly electron accepting (γ+). For substrates surfaces, we found that both sea-immersed stainless steels types were hydrophilic and present strong electron-donor character (γ− = 49 ± 0.2 mJ m−2 for 304 and γ− = 55.07 ± 0.02 mJ m−2 for 316) and weak electron-acceptor character (γ+ = 5.4 ± 0.1 mJ m−2 for 304 and γ+ = 8.3 ± 0.06 mJ m−2 for 316). The theoretical prediction showed that both tested strains, B. thuringiensis and B. amyloliquefascience, exhibited positive values of ΔGTotal vis-à-vis the two sea-immersed stainless steels types which indicates unfavorable adhesion while the ESEM electro-micrographs show that both strains were able to adhere to both strainless steels surfaces.

Fabrication Processes to Generate Concentration Gradients in Polymer Solar Cell Active Layers

Polymer solar cells (PSCs) are considered as one of the most promising low-cost alternatives for renewable energy production with devices now reaching power conversion efficiencies (PCEs) above the milestone value of 10%. These enhanced performances were achieved by developing new electron-donor (ED) and electron-acceptor (EA) materials as well as finding the adequate morphologies in either bulk heterojunction or sequentially deposited active layers. In particular, producing adequate vertical concentration gradients with higher concentrations of ED and EA close to the anode and cathode, respectively, results in an improved charge collection and consequently higher photovoltaic parameters such as the fill factor. In this review, we relate processes to generate active layers with ED–EA vertical concentration gradients. After summarizing the formation of such concentration gradients in single layer active layers through processes such as annealing or additives, we will verify that sequential deposition of multilayered active layers can be an efficient approach to remarkably increase the fill factor and PCE of PSCs. In fact, applying this challenging approach to fabricate inverted architecture PSCs has the potential to generate low-cost, high efficiency and stable devices, which may revolutionize worldwide energy demand and/or help develop next generation devices such as semi-transparent photovoltaic windows.

The effect of permodified cyclodextrins encapsulation on the photophysical properties of a polyfluorene with randomly distributed electron-donor and rotaxane electron-acceptor units.

We report on the synthesis as well as the optical, electrochemical and morphological properties of two polyrotaxanes (4a and 4b), which consist of electron-accepting 9,9-dicyanomethylenefluorene 1 as an inclusion complex in persilylated β- or γ-cyclodextrin (TMS-β-CD, TMS-γ-CD) (1a, 1b) and methyltriphenylamine as an electron-donating molecule. They are statistically distributed into the conjugated chains of 9,9-dioctylfluorene 3 and compared with those of the corresponding non-rotaxane 4 counterpart. Rotaxane formation results in improvements of the solubility, the thermal stability, and the photophysical properties. Polyrotaxanes 4a and 4b exhibited slightly red-shifted absorption bands with respect to the non-rotaxane 4 counterpart. The fluorescence lifetimes of polyrotaxanes follow a mono-exponential decay with a value of τ = 1.14 ns compared with the non-rotaxane, where a bi-exponential decay composed of a main component with a relative short time of τ1 = 0.88 (57.08%) and a minor component with a longer lifetime of τ2 = 1.56 ns (42.92%) were determined. The optical and electrochemical band gaps (ΔEg) as well as the ionization potential and electronic affinity characterized by smaller values compared to the values of any of the constituents. AFM reveals that the film surface of 4a and 4b displays a granular morphology with a lower dispersity supported by a smaller roughness exponent compared with the non-rotaxane counterpart.

Impact of the exopolysaccharides Pel and Psl on the initial adhesion of Pseudomonas aeruginosa to sand

In this study, the impact of the exopolysaccharides Pel and Psl on the cell surface electron donor-electron acceptor (acid-base) properties and adhesion to quartz sand was investigated by using Pseudomonas aeruginosa PAO1 and its isogenic EPS-mutant strains Δpel, Δpsl and Δpel/Δpsl. The microbial adhesion to hydrocarbon (MATH) test and titration results showed that both Pel and Psl contribute to the surface hydrophobicity of the cell. The results of contact angle measurement, however, showed no correlation with the cell surface hydrophobicity measured by the MATH test and the titration method. Packed-bed column experiments indicated that the exopolysaccharides Pel and Psl are involved in the initial cell attachment to the sand surface and the extent of their impact is dependent on the ionic strength (IS) of the solution. Overall, the Δpel/Δpsl double mutant had the lowest adhesion coefficient to sand compared with the wild-type PAO1, the Δpel mutant and the Δpsl mutant. It is hypothesized that in addition to bacterial surface hydrophobicity and DLVO forces, other factors, eg steric repulsion caused by extracellular macromolecules, and cell surface appendages (flagella and pili) also contribute significantly to the interaction between the cell surface and a sand grain.

The influence of the nematic phase on the phase separation of blended organic semiconductors for photovoltaics

Differential scanning calorimetry in combination with atomic force microscopy is used to examine the phase separation of a blended nematic liquid crystalline electron-donor and crystalline perylene electron-acceptor mixture. Separate domains of donor and acceptor material are mostly retained in the blend, although a small proportion of the acceptor, increasing with increasing donor concentration, is mixed in with the donor domains. Annealing in the nematic phase allows the donor and acceptor molecules to move and generate phase-separated domains of the required size, thus enhancing the performance of bulk heterojunction photovoltaic devices based on these blends. We show that the optimum annealing temperature can be controlled by manipulation of the temperature range of the nematic phase of the donor.

Proton-Coupled Electron Transfer with Photoexcited Metal Complexes

Proton-coupled electron transfer (PCET) plays a crucial role in many enzymatic reactions and is relevant for a variety of processes including water oxidation, nitrogen fixation, and carbon dioxide reduction. Much of the research on PCET has focused on transfers between molecules in their electronic ground states, but increasingly researchers are investigating PCET between photoexcited reactants. This Account describes recent studies of excited-state PCET with d(6) metal complexes emphasizing work performed in my laboratory. Upon photoexcitation, some complexes release an electron and a proton to benzoquinone reaction partners. Others act as combined electron-proton acceptors in the presence of phenols. As a result, we can investigate photoinduced PCET involving electron and proton transfer in a given direction, a process that resembles hydrogen-atom transfer (HAT). In other studies, the photoexcited metal complexes merely serve as electron donors or electron acceptors because the proton donating and accepting sites are located on other parts of the molecular PCET ensemble. We and others have used this multisite design to explore so-called bidirectional PCET which occurs in many enzymes. A central question in all of these studies is whether concerted proton-electron transfer (CPET) can compete kinetically with sequential electron and proton transfer steps. Short laser pulses can trigger excited-state PCET, making it possible to investigate rapid reactions. Luminescence spectroscopy is a convenient tool for monitoring PCET, but unambiguous identification of reaction products can require a combination of luminescence spectroscopy and transient absorption spectroscopy. Nevertheless, in some cases, distinguishing between PCET photoproducts and reaction products formed by simple photoinduced electron transfer (ET) (reactions that don't include proton transfer) is tricky. Some of the studies presented here deal directly with this important problem. In one case study we employed a cyclometalated iridium(III) complex. Our other studies with ruthenium(II) complexes and phenols focused on systematic variations of the reaction free energies for the CPET, ET, and proton transfer (PT) steps to explore their influence on the overall PCET reaction. Still other work with rhenium(I) complexes concentrated on the question of how the electronic structure of the metal-to-ligand charge transfer (MLCT) excited states affects PCET. We used covalent rhenium(I)-phenol dyads to explore the influence of the electron donor-electron acceptor distance on bidirectional PCET. In covalent triarylamine-Ru(bpy)₃²⁺/Os(bpy)₃²⁺-anthraquinone triads (bpy = 2,2'-bipyridine), hydrogen-bond donating solvents significantly lengthened the lifetimes of photogenerated electron/hole pairs because of hydrogen-bonding to the quinone radical anion. Until now, comparatively few researchers have investigated this variation of PCET: the strengthening of H-bonds upon photoreduction.

Resistive Polymer Memory Materials Containing Electron Donor and Acceptor Moieties

Two series of polymers including polyimides and poly(aryl ether)s were prepared and used as active layers of polymer memories. The poly(aryl ether)-based polymers showed flash behaviors and polyimide-based polymers showed WORM behaviors. The poly(aryl ether)s flash memories can be negatively switched on and positively switched off, and the switching voltages are relative to the chemical structure of bisphenol moiety. On the other hand, the polyimide-based polymer devices can be bidirectionally switched on with comparable positive and negative switching threshold voltages, but cannot be switched off. The polyimides showed write-once-and-read- many-times (WORM) memory behavior. The poly(aryl ether) (AZTA-PAEb) showed very different memory behavior from polyimides (AZTA-PI and AZTA-PEI) although they contain the similar chemical structure (electron-donor triphenylamine and electron-acceptor triazine moieties). The imide structure in the polyimides plays a great role in the memory effects.

On the influence of the exciton-blocking layer on the organic multilayer cells properties

The performances of organic photovoltaic cells based on the layer couple electron donor/electron acceptor (ED/EA) are significantly improved when an exciton blocking layer (EBL) is inserted between the organic acceptor and the cathode. A new material, the (Z)-5-(4-chlorobenzylidene)-3-(2-ethoxyphenyl)-2-thioxothiazolidin-4-one, that we called (CBBTZ), has been synthesized, characterized and probed as EBL. The energy levels corresponding to the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the CBBTZ have been determined from the first oxidation and reduction potential respectively, using cyclic voltametric (CV) measurements. From CV curves, CBBTZ in dichloromethane showed a one electron reversible reduction and oxidation waves. The values of its HOMO and LUMO have been estimated to be 6.42 eV and 3.42 eV respectively. Such values show that CBBTZ could be probed as EBL in organic solar cells based on the ED/EA couple copper phthalocyanine(CuPc)/fullerene (C 60 ). The photovoltaic solar cells have been obtained by sequential deposition under vacuum of the different films. The different thin film thicknesses were measured in situ by a quartz monitor. Multilayer solar cells ITO/Au/CuPc/C 60 /EBL/Al have been probed, where EBL is the aluminium tris(8-hydroxyquinoline) (Alq 3 ), the CBBTZ, the 2-(4-byphenylyl)-5-(4-tert-buthylphenyl)-1,3,4-oxadiazole (butyl PBD) or the bathocuproine (BCP). The optimum film thickness is 8–9 nm whatever the EBL used. When obtained in the same run, the averaged efficiency of the cells using the CBBTZ is of the same order of magnitude than that obtained with BCP and higher than that achieved with Alq 3 or butyl PBD. It is shown by XPS study that some aluminium of the cathode is present in the buffer layer. This aluminium could justify the ability of the electrons to cross the insulating exciton blocking layer thick of 9 nm.

Ab initio Study of the Interactions between CO2 and N‐Containing Organic Heterocycles

In the garden of dispersion: High-accuracy ab initio calculations are performed to determine the nature of the interactions and the most favorable geometries between CO(2) and heteroaromatic molecules containing nitrogen (see figure). Dispersion forces play a key role in the stabilization of the dimer, because correlation effects represent about 50 % of the total interaction energy. The interactions between carbon dioxide and organic heterocyclic molecules containing nitrogen are studied by using high-accuracy ab initio methods. Various adsorption positions are examined for pyridine. The preferred configuration is an in-plane configuration. An electron donor-electron acceptor (EDA) mechanism between the carbon of CO(2) and the nitrogen of the heterocycle and weak hydrogen bonds stabilize the complex, with important contributions from dispersion and induction forces. Quantitative results of the binding energy of CO(2) to pyridine (C(5)H(5)N), pyrimidine, pyridazine, and pyrazine (C(4)H(4)N(2)), triazine (C(3)H(3)N(3)), imidazole (C(3)H(4)N(2)), tetrazole (CH(2)N(4)), purine (C(5)H(4)N(4)), imidazopyridine (C(6)H(5)N(3)), adenine (C(5)H(5)N(5)), and imidazopyridamine (C(6)H(6)N(4)) for the in-plane configuration are presented. For purine, three different binding sites are examined. An approximate coupled-cluster model including single and double excitations with a perturbative estimation of triple excitations (CCSD(T)) is used for benchmark calculations. The CCSD(T) basis-set limit is approximated from explicitly correlated second-order Møller-Plesset (MP2-F12) calculations in the aug-cc-pVTZ basis in conjunction with contributions from single, double, and triple excitations calculated at the CCSD(T)/6-311++G** level of theory. Extrapolations to the MP2 basis-set limit coincide with the MP2-F12 calculations. The results are interpreted in terms of electrostatic potential maps and electron density redistribution plots. The effectiveness of density functional theory with the empirical dispersion correction of Grimme (DFT-D) is also examined.

Turning on Fluorescent Emission from C-Alkylation on Quinoxaline Derivatives

Reduction on imine moiety (C=N) of quinoxalines by alkyl-/aryllithiums led to a geometrical change on the quinoxaline ring, thereby perturbing the electronic structure to turn on fluorescence emission. Such a structural change resulted in interrupted cyclic-ring systems with electron-donating amine (sp(3)-type) and electron-accepting imine (sp(2)-type) units bridged by a phenylene unit. Through either alkylation or arylation, a highly polarized electron donor-electron acceptor bipolar system was established in a single molecule with dramatically enhanced PL efficiency (up to 60%).

Spectrophotometric study of interaction of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone with diaza-18-crown-6 and diaza-15-crown-5 in acetonitrile and chloroform solutions

Interactions of diaza-18-crown-6 and diaza-15-crown-5, as electron donors, with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), as an electron acceptor, have been investigated spectrophotometrically in acetonitrile and chloroform solutions. The results indicated immediate formation of an electron donor-electron acceptor complex DA: D + A ⇌ fast K f DA which is followed by two relatively slow consecutive reactions: DA ⟶ k 1 D + A − ⟶ k 2 Product The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance time data to appropriate equations. The formation constants of the resulting DA complexes have also been determined. The influences of both the azacrown’s structure and the solvent properties on the formation of DA complexes and the rates of subsequent reactions are discussed.

Does the back electron transfer affect the rate of photoinducec free radical polymerization?

The specific behaviors of monomeric electron acceptor-electron donor bridged molecules and of polymeric initiator-coinitiator systems tested as free radical polymerization photoinitiating systems were observed. The obtained experimental and theoretical results suggest that the back electron transfer process probably does not control the rate of photoinitiated polymerization going with initiators tested. The phenomena observed more likely results from a different proton transfer between Rose bengal radical anion and a tertiary aromatic amine radical cation. This can be deducted on the basis of Marcus theory, describing the kinetics of photoinduced intermolecular and intramolecular electron transfer processes, and laser flash photolysis measurements.

Nonlinear optical properties of some side chain copolymers based on benzoxazole containing chromophores

Acrylate-methylmethacrylate copolymers have been synthesized for nonlinear optical applications. Acrylate monomer units are characterized by the presence in the side chain of phenylbenzoxazole groups containing electron donor-electron acceptor substituents. The phase behavior of all polymers has been investigated by DSC, X-ray diffraction and polarizing microscopy: two of them exhibit liquid crystalline behavior of smectic type. For four polymers, nonlinear optical properties have been examined by second harmonic generation measurements on thin films (∼ 1 μm thickness) electrically poled by corona discharge. Second order susceptibility coefficients d33 and average relaxation times 〈τ〉, relative to the time stability of the chromophore poling, have been measured. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 603–608, 1999

INHIBITORY EFFECTS OF 2-MERCAPTOBENZOTHIAZOLE ON MICROBIAL GROWTH IN A VARIETY OF TROPHIC CONDITIONS

2-Mercaptobenzothiazole (MBT) is found mainly in the wastewaters of its industrial production as a rubber vulcanization accelerator. Because this compound was found to be toxic to activated sludges and because it causes poor process performances, its impact on bacteria in particular was studied. 2-Mercaptobenzothiazole, but not other benzothiazoles, exerted mainly bacteriostatic effects towards Escherichia coli, Sarcina lutea, Staphylococcus aureus, and a 2-hydroxybenzothiazole-degrading isolate (OBT18). It caused membrane disturbance as measured by induced potassium effluxes from the cell. Emphasis was on the effects of MBT on growth of E. coli on different electron donor-electron acceptor combinations. Paracoccus denitrificans was grown in the presence of oxygen or nitrate and the yeast Saccharomyces cerevisiae was used under aerobic and fermentative conditions. In almost all conditions the growth was severely inhibited, indicating that MBT might interfere with a common oxidoreduction step in membrane-bound systems and probably also interferes with metabolic reactions not related to the respiratory chain.

Capillary Gas-Chromatographic Retention Behavior and Physico-Chemical Properties of Underivatized Equine Estrogens

The capillary gas-chromatographic retention behavior of six underivatized equine estrogens (estrone, equilin, equilenin and their corresponding 17α-diols) on a mixed stationary phase (non-polar CP-Sil 5 CB and slightly polar CP-Sil 19 CB capillary columns coupled in series) was characterized by their Kovats retention indices and steroid numbers. In order to find whether a correlation exists between the chromatographic retention and some physico-chemical properties of the compounds, their octanol-water partition coefficients and dipole moments were measured. No straightforward correlation was observed between the physico-chemical properties and the retention behavior, which suggests that the GC separation of equine estrogens is governed by some specific electron donor-electron acceptor interactions of a chemical nature.

Influence of spacer length between interacting group and polymer backbone on the glass transition temperature of electron-donor/electron-acceptor blends

Charge transfer Interaction (CT-I) between electron-donor/electron-acceptor groups contributes to an enhancement of the miscibility in polymer blends. Typical of polymer blends with charge transfer interaction is an increase of the glass transition temperature, suggesting a decrease of the free volume during mixing of the blend components. Both, “zip”-like orientation effects of the CT-I onto the polymer backbones and temporary crosslink formation may contribute to the reduction of the free volume. The effect generally decreases with increasing spacer length between the interacting groups and the polymer backbone, although an increased probability of electron-donor/electron acceptor (EDA) association may be accepted due to the enhanced mobility of the interacting endgroups. Thus the increased probability of EDA association is overcome both by the increased mobility of the temporary crosslinks and by the decrease of the induced orientation effect on the polymer backbone of the CT-I due to the enhanced decoupling of the mobile interacting groups from the less mobile polymer backbone. Because of the possibility of D/2A association of the carbazolyl end-group the effect is more complicated. For the same overall spacer length of the interacting EDA groups the deviation from the additivity of the glass transition temperatures of the polymer blend components is always the larger the longer the donor-spacer.