Strong Electron Acceptor Research Articles

Исследование молекулярной и электронной структуры полициклических ароматических углеводородов каменноугольной смолы

The molecular and electronic structure of coal tar asphaltenes was investigated. The objects of the study are asphalt resins of coking Kuzbass coal. Solution absorption spectra in the range of 310-780 nm were recorded on a СФ-2000 spectrophotometer. In the process of studying the absorption spectra of asphaltenes by optical spectroscopy, it has been found that the asphaltene fraction is a strong donor and electron acceptor. Effective ionization potential (6.64 eV), effective electron affinity (1.20 eV) and band gap width (5.44 eV) have been established. The study of the electronic structure of molecules of polycyclic aromatic hydrocarbons (PAHs), which are nuclei of molecules of asphaltenes of the "continental" type, was carried out by the method of DFT/B3LYP with the basic set 6-31+G*, using the software package GAUSSIAN. Quantum-chemical calculations have shown that the first vertical ionization potential is equal to that the first vertical ionization potential is in the range of 6.41 to 6.71 eV, affinity to the electron – from 0.79 to 1.08 eV, values of the gap zone width – from 5.33 to 5.92 eV. Dipole moments of asphaltenes (0.32 to 0.46 D) were calculated. The calculation data confirm the hypothesis of increased donor-acceptor capacity of asphalt-resin substances.

Gap states induce soft Fermi level pinning upon charge transfer at ZnO/molecular acceptor interfaces

The deposition of strong molecular electron acceptors onto ZnO induces a substantial work function (\ensuremath{\phi}) increase due to electron transfer from the inorganic semiconductor to the molecules. The \ensuremath{\phi} increase results from two mechanisms: (i) a change of the surface band bending within ZnO and (ii) an interface dipole between the inorganic surface and the negatively charged acceptors. The molecule adsorption induced upward band bending in ZnO is, however, found to be limited to a few 100 meV, while the \ensuremath{\phi} increase is significantly larger (up to 2.8 eV). We elucidate the origin of limited upward band bending by revealing a notable gap state density-of-states (GDOS) using high-sensitivity photoemission spectroscopy. Upon acceptor-induced upward band bending, the GDOS with a wide energy distribution becomes increasingly unoccupied. This, in turn, makes the interface dipole dominant and limits the ZnO surface band bending changes due to a ``soft'' pinning at the Fermi level.

Optoelectronic and Electronic Properties of Tetracyanoindane for Chemical Doping of Organic Semiconductors

ABSTRACTChemical doping of organic semiconductors is a common technique used to increase the performance numerous organic electronic and optoelectronic devices. Tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) is one of the most widely known p-dopants having the properties necessary to act as a strong electron acceptor. Despite its strong electron accepting abilities, F4-TCNQ is extremely expensive, making it less than ideal for large-area applications. Here, we introduce a small molecule called Tetracyanoindane (TCI) as a potential p-dopant. Widely known for its role in the field of non-linear optics, its high polarizability arises from the addition of four cyano-groups, which are electron withdrawing groups. The four cyano-groups are also seen in the F4-TCNQ molecule and contributes to the withdrawing strength alongside the four fluorine atoms present. We hypothesize that TCI could have similar accepting strength to F4-TCNQ and could potentially replace it as a cheaper alternative. In this study, Cyclic Voltammetry (CV), UV-Visible-Near Infrared Spectroscopy (UV/Vis/NIR), Photoluminescence (PL), Current-Voltage (IV) measurements analysis was conducted to compare the accepting strength of TCI and F4-TCNQ. Then, the two molecules were added to Poly-3-hexy-thiophene (P3HT) to observe how readily they dope the organic semiconductor.

Determination of the mechanism of interaction of humic acids of peats with a strong electron acceptor - bromanil

The binding capacity of humic acids of peats in the relation to bromoanil is determined. It is shown the percentage of binding of bromoanil with humicacids and hymatomelanoic acids has similar values and does not exceed 18%, which indicates a minimal contribution of donor-acceptor interaction in the process of binding polyaromatic hydrocarbons with humic acids. It has been proved that the leading role in the binding of humic acids with polyaromatic hydrocarbons belongs to intermolecular hydrophobic interactions, which leads to the formation of supramolecular structures between the aromatic core of humic acids and polyaromatic hydrocarbons.

Synthesis of a tetrazine\u2013quaterthiophene copolymer and its optical, structural and photovoltaic properties

Herein, we report the synthesis of a novel, tetrazine-based conjugated polymer. Tetrazines have the benefit of being strong electron acceptors, while little steric hindrance is imposed on the flanking thiophene rings. Conversion of a suitably substituted nitrile precursor led to 3,6-bis(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-1,2,4,5-tetrazine (2OD-TTz). Palladium-catalyzed copolymerization of 2OD-TTz with a bithiophene monomer yielded an alternating tetrazine–quaterthiophene copolymer (PTz4T-2OD). The polymer PTz4T-2OD showed an optical band gap of 1.8 eV, a deep HOMO energy level of − 5.58 eV and good solubility. In combination with the non-fullerene acceptor ITIC-F, solar cells with power conversion efficiencies of up to 2.6% were obtained.

A comparative study of S···π chalcogen bonds between SF2 or SFH and C[sbnd]C multiple bonds

We theoretically study chalcogen bonds involving SF2 and SFH, each paired with various unsaturated hydrocarbons ethyne, ethene, 1,3-butadiene, and benzene. The binding energies are calculated at theory level MP2, M06-2X-D3 and CCSD(T)/CBS, respectively. Geometry structure, binding energies, interaction type and strength are studied comparatively. SFH engages in a stronger chalcogen bond than does SF2 for all systems, which indicates that SFH is a stronger electron acceptor than SF2. Two kinds of energetic effects are observed, SF2···cis-butadiene complex contain the strongest chalcogen bond among all the SF2···π complexes, which is attributed to the energetic effect of two S···π interactions. For SFH···π complexes, the strongest interaction is formed between SFH and C6H6, which can be explained by the synergistic effects of the S···π and SH···π interaction. The largest charge transfer arises from the occupied CC bonding orbital to the σ*(SF) antibonding orbital. The quantity is considerably larger for SFH than for SF2.

Modulation of the Work Function by the Atomic Structure of Strong Organic Electron Acceptors on H‐Si(111)

AbstractAdvances in hybrid organic/inorganic architectures for optoelectronics can be achieved by understanding how the atomic and electronic degrees of freedom cooperate or compete to yield the desired functional properties. Here, how work function changes are modulated by the structure of the organic components in model hybrid systems is shown. Two cyano‐quinodimethane derivatives (F4‐TCNQ and F6‐TCNNQ), which are strong electron‐acceptor molecules, adsorbed on H‐Si(111) are considered. From systematic structure searches employing the range‐separated hybrid HSE06 functional including many‐body van der Waals (vdW) contributions, it is predicted that, despite their similar composition, these molecules adsorb with significantly different densely packed geometries in the first layer, due to strong intermolecular interaction. F6‐TCNNQ shows a much stronger intralayer interaction (primarily due to vdW contributions) than F4‐TCNQ in multilayered structures. The densely packed geometries induce a large interface‐charge rearrangement that results in a work function increase of 1.11 and 1.76 eV for F4‐TCNQ and F6‐TCNNQ, respectively. Nuclear fluctuations at room temperature produce a wide distribution of work function values, well‐modeled by a normal distribution with σ = 0.17 eV. These findings are corroborated with experimental evidence of pronounced island formation for F6‐TCNNQ on H‐Si(111) and with the agreement of trends between predicted and measured work function changes.

Molecular Doping of a Water‐Soluble Polythiophene Derivative

Intrinsic conducting polymers are promising candidates for bioelectronic devices due to their structural kinship to biological matter combined with electronic functionality. For sophisticated nano‐scaled bioelectronic devices, P3RT‐type polythiophene derivatives bearing water‐soluble, biocompatible sidechains are particularly appealing due to their well‐defined molecular structure and controllable end‐group composition. However, their employment in bioelectronic devices is not as straightforward as expected. Challenging is their poor performance due to, e.g., the low charge carrier concentration in the native state. Partial oxidation of these polymers by strong electron acceptors, so‐called p‐type doping, can increase the charge carrier concentration, and thus, the conductivity. The solution‐based molecular p‐type doping of such a water‐soluble polythiophene derivative by the dopant tetrafluoro‐tetracyano‐quinodimethane is reported. The mechanism of the doping process is thoroughly investigated by a combination of spectroscopic techniques covering the UV‐VIS and IR regions. Furthermore, the morphological and electronic properties of polymer thin films are examined as a dependence on the dopant concentration.

High-Performance Resistance-Switchable Multilayers of Graphene Oxide Blended with 1,3,4-Oxadiazole Acceptor Nanocomposite.

Graphene oxide (GO) has been actively utilized in nonvolatile resistive switching random access memory (ReRAM) devices due to solution-processability, accessibility for highly scalable device fabrication for transistor-based memory, and cross-bar memory arrays. Uncontrollable oxygen functional groups of GO, however, restrict its application. To obtain stable memory performance, 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) a that can serve as 1,3,4-oxadiazole acceptor was carefully introduced onto the GO framework. Better stability was achieved by increasing the weight ratio of the chemical component from 2:1 to 10:1 in all GO-based solutions. Particularly, rewritable nonvolatile memory characteristics were dependent on the ratio between PBD and GO. PBD:GO devices with a proportion of 10:1 w/w exhibited better memory performance, possessed a higher ON/OFF ratio (>102) at a lower switching voltage of −0.67 V, and had a long retention ability. The interaction between PBD and GO can be demonstrated by transmission electron microscope, scanning electron microscope, thermogravimetric analysis, fourier transform infrared spectra, Raman spectra, X-ray diffraction, and fluorescence spectra. The superior ReRAM properties of the multilayers of GO blended with the PBD nanocomposite are attributed to electron traps caused by the strong electron acceptors.

Fractional and Integer Charge Transfer at Semiconductor/Organic Interfaces: The Role of Hybridization and Metallicity.

Inorganic/organic interfaces show two phenomenologically different types of charge transfer: On inert substrates, charge is localized, leading to a coexistence of neutral and charged molecules. Conversely, on metals, which have more available charge carriers and a larger propensity to hybridize, the charge is homogeneously delocalized. In this contribution, we use hybrid density functional theory to study the adsorption of the strong electron acceptor F4TCNQ on ZnO(10-10) as a function of the substrate's doping concentration. This system undergoes a joint charge donation/backdonation reaction. Because only the former is driven by hybridization, this allows us to study the impact of hybridization and the availability of charge carriers separately. We find that here both charge-transfer types are simultaneously at work. Whereas hybridization determines the charge localization, the charge-carrier concentration determines the amount of transferred charge. Consequently, at low doping concentrations, most of the electron acceptors become slightly positively, rather than negatively, charged.

VIRTUAL SCREENING OF HETEROCYCLIC COMPOUNDS AGAINST ANGIOTENSIN-CONVERTING ENZYME FOR POTENTIAL ANTIHYPERTENSIVE INHIBITORS

Objective: The objective of this study was to investigate the antihypertensive activity of heterocyclic compounds against angiotensin-converting enzyme (ACE) through molecular docking studies.
 Methods: The X-ray crystal three-dimensional (3D) structure of human ACE complexed with lisinopril (PDB ID: 1O86) was retrieved from protein databank. The two-dimensional structures of 10 selected heterocyclic compounds were drawn in ACD-Chemsketch and converted into 3D structures. The 3D structures of compounds were virtually screened in the binding pockets of ACE using FlexX docking program. Further, the chemical entities revealing the molecular electronic structures of the best docked compound (Compound-4) were explored through density functional theory studies.
 Results: The Compound-4 showed the highest docking score of −26.6290 kJ/mol with ACE. The Hbond and non-bonded interactions are favored by phenylalanine, leucine, and arginine. The energy gap of 1.60 eV between highest occupied molecular orbital and lowest unoccupied molecular orbitals explained the presence of strong electron-acceptor group. Furthermore, the molecular electrostatic potential studies clearly envisaged the requirement of electropositive and electronegative groups are crucial for the ACE inhibitor activities.
 Conclusion: The identification of good ACE inhibitors requires the understanding of the current ACE inhibitors. Thus, the docking interactions of Compound-4 and its molecular electronic structure significantly imply its potential as antihypertensive agent. However, further clinical studies are required to ascertain its potential toxic effects.

Optimization of the thermoelectric performance of layer-by-layer structured copper-phthalocyanine (CuPc) thin films doped with hexacyano-trimethylene-cyclopropane (CN6-CP).

Copper-phthalocyanine (CuPc), as a classical small molecular organic semiconductor, has been applied in many fields. However, the low intrinsic conductivity limits its application in thermoelectricity. Here, hexacyano-trimethylene-cyclopropane (CN6-CP), a strong electron acceptor, is synthesized as dopant for CuPc thin films to improve their conductivities. Multilayer thin films constructed from alternate thermally evaporated CuPc and CN6-CP thin layers are investigated. Under the optimized condition, the doped CuPc film with a conductivity of 0.76 S cm−1 and a Seebeck coefficient of 130 μV K−1, shows a high power factor of 1.3 μW m−1 K−2 and the carrier concentration is estimated to be 2.8 × 1020 cm−3. Considering the relatively superior performance, the CN6-CP doped CuPc film is a promising small molecular organic thermoelectric (OTE) material. In addition, for those highly crystalline materials with poor solubility, the layer-by-layer structure offers a general strategy for investigation and optimization of their TE performance.

Structure-property relationship of novel monosubstituted Ru (II) complexes for high photocurrent and high efficiency DSSCs: Influence of donor versus acceptor ancillary ligand on DSSCs performance

Two novel high molar extinction coefficient monosubstituted-bipy Ru (II) complexes, IA-5 and IA-6, based on D-D-π and π-A-π-A ancillary ligands were synthesized with the aid of Knoevenagel reaction, to study the influence of the electron donor and electron acceptor ancillary ligand and number of anchoring group (COOH) on the light harvesting efficiency (LHE), ground and excited state oxidation potentials, incident-photon-to-current conversion efficiency (IPCE), short-circuit photocurrent density (J), and total solar-to-electric conversion efficiency (%η) for DSSCs, and their device performances were studied and showed a maximum of PCE of 7.81% (JSC = 17.61 mA cm−2, VOC = 0.69 V and FF = 64.05%) for dye IA-6 compared to PCE of 7.74% (JSC = 15.83 mA cm−2, VOC = 0.74 V and FF = 65.37%) for N719 dye. The photophysical and photoelectrochemical properties discussed herein addressed the significant impact of the electron donor and electron acceptor ancillary ligand and the number of anchoring groups on JSC and %η in DSSCs. The molecular structures of IA-5 and IA-6 were characterized using UV–Vis, emission spectrophotometry, FT-IR, ESI-MS, and 1H NMR.To probe the interrelationship between the chemical structure, photophysical and photoelectrochemical properties, molecular modeling studies, implemented in Gaussian, were employed. DFT/TD-DFT calculations were used to calculate the thermodynamics and electronic properties of IA-5 and IA-6 including HOMO and LUMO isosurfaces, lowest singlet-singlet electronic transitions (E0-0), ground and excited states oxidation potentials, GSOP and ESOP, which were in excellent agreement with the experimental results. Surprisingly, the insertion of the strong electron acceptor benzodithiazole in the ancillary ligand of IA-5 showed that the frontier LUMO shifted by 100% from 2,2′-bipyridyl-4,4′-dicarboxlic acid to the ancillary ligand containing benzodithiazole with electron injection accomplished from the anchoring group tethered to benzodithiazole. This new finding of relocating the LUMO from bipy-dicarboxylic acid to the other ancillary ligand would open the door for the molecular engineering of better light harvesting and more efficient Ru (II) complexes for DSSCs.

Unraveling the Microstructure of Molecularly Doped Poly(3-hexylthiophene) by Thermally Induced Dedoping

We exploited the thermal annealing of poly(3-hexylthiophene) (P3HT) molecularly p-doped with the strong electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) as a tool for tuning the doping concentration as a quasi singular parameter. Via directed dopant desorption, we could unravel the complex microstructure of this semicrystalline system, leading to a detailed growth model solely based on complementary experimental evidence from scattering and spectroscopic techniques. We find the crystalline portion of p-doped P3HT to comprise regions, where dopant anions pack with the polymer chains in a metastable, cocrystalline structure with additional ionized dopants dispersed in the alkyl chain region of P3HT. Simultaneously, regions exist where the pristine polymer backbones closely pack. The dedoping via dopant desorption through thermal annealing reveals the dopants within the mixed crystalline phase to be thermally least stable. Notably, their initial desorption does not alter the th...

Enhancing photoconductivity of aromatic polyimide films by incorporating fluorinated dianhydrides and main chain triphenylamine structure

The photoconductive properties of seven types of fully aromatic polyimide (PI) films with a main chain triphenylamine structure were investigated by examining the wavelength dependence of photo-irradiation in the visible region under a direct current (DC) electric field. It was clarified that the out-of-plane photoconductivity of the PIs synthesized from seven types of dianhydrides and 4,4′-diamino-4″-methyltriphenylamine (DATPA) tends to increase as the intramolecular charge transfer (CT) interactions increase, which is essentially dominated by the electron accepting properties of the dianhydrides. In particular, the PIs derived from the pyromellitic dianhydrides substituted by two fluoro (−F) or one trifluoromethyl (−CF3) substitutes with strong electron accepting properties (P2FDA/DATPA and P3FDA/DATPA) exhibited significantly enhanced photoconductivity with relatively strong optical absorbance in the visible region. Moreover, the P6FDA/DATPA PI prepared from pyromellitic dianhydrides and substituted by two bulky CF3 substitutes exhibited intense optical absorbance but lower photoconductivity, owing to the enlarged interchain distance, as evaluated by the out-of-plane GI-WAXS pattern. This suggests that the charged carriers are preferentially transported along the interchain directions, and the photoconductivity of the PI films is significantly influenced, not only by the degree of intramolecular CT interactions, but also by the polymer aggregation structures facilitating the interchain charge transportation.

Fluorosolvatochromism and hyperpolarizability of one-arm and two-arms nitro-compounds bearing heterocyclic rings

We report here the spectral characterization and hyperpolazizatin coefficinet of all-trans isomers of two-branched push-pull systems of interest as new efficient organic materials for Non Linear Optics, compared with the corresponding mono-branched analogues. These molecules are characterized by Acceptor-π-Het-π-Acceptor and Acceptor-π-Het structures, respectively, where the strong electron acceptor is the nitro group and the electron rich portion is a heteroaromatic ring (pyridine, furan and thiophene). These compounds exhibit strong fluorosolvatochromism, in agreement with the substantial photoinduced intramolecular charge transfer (from the heteroaromatics to the nitro groups) undisclosed by quantum mechanical calculations. The hyperpolarizability of these molecules, here estimated by the solvatochromic method, reaches significant values in all cases: enhanced for the two-branched systems with respect to their mono-branched analogues and higher for the furan/thiophene derivatives with respect to the pyridine ones. Surprisingly, hyperpolarizabilities of the symmetrical Acceptor-π-Het-π-Acceptor structures are found to be similar or higher than those of the asymmetrical Acceptor-π-Het-π-Donor counterparts.

Charge Transfer at the Interface Between MnPc and F6TCNNQ

Photoelectron spectroscopy in the core level as well as the valence band region has been used to determine the electronic properties of interfaces between manganese phthalocyanine (MnPc) and the strong electron acceptor F6TCNNQ. It is shown that charge transfer occurs at this interface which results in the oxidation (reduction) of MnPc (F6TCNNQ) at the interface. Our data indicate a full electron transfer with no evidence for hybrid states. The valence band data suggest that the interface remains insulating/semiconducting despite the charge transfer, which indicates localized charges.

NIR-Absorbing Dye Based on BF2-Bridged Azafulvene Dimer as a Strong Electron-Accepting Unit.

BF2-bridged azafulvene dimers designed to be strong electron-accepting units were selectively synthesized using a bulky base. Single-crystal X-ray diffraction analysis revealed that the high electron-accepting ability of this structure stems from the contribution of the π-conjugation mode of the azafulvene dimer upon formation of B-N coordination bonds. As a result of the low-lying LUMO energy of this electron-accepting unit, the corresponding D-A-D dye exhibits an intense NIR absorption band at 922 nm, which tails up to 1150 nm, while significant absorption bands in the visible region are absent. As a NIR dye this molecule exhibits moreover exceptional photostability and resistance to oxidation by atmospheric oxygen, even in dilute solution.

Multifunctional Additives Improve the Electrolyte Properties of Magnesium Borohydride Toward Magnesium-Sulfur Batteries.

Highly reductive magnesium borohydride [Mg(BH4)2] is compatible with metallic Mg, making it a promising Mg-ion electrolyte for rechargeable Mg batteries. However, pure Mg(BH4)2 in ether-based solutions displays very limited solubility (0.01 M), low oxidative stability (<1.8 V vs Mg), and nucleophilic characteristic, all of which preclude its practical utilization for any battery applications. Herein, we present a multifunctional additive of tris(2 H-hexafluoroisopropyl)borate (THFPB) for preparing Mg(BH4)2-based electrolytes. By virtue of the strong electron-acceptor ability of the THFPB molecule, a transparent and high-concentration Mg(BH4)2/THFPB-diglyme (DGM) electrolyte (0.5 M, almost 50 times higher than that of the pristine Mg(BH4)2-DGM electrolyte) is first obtained, which shows dramatic performance improvements, including high ionic conductivity (3.72 mS cm-1 at 25 °C) and high Mg plating/stripping Coulombic efficiency (>99%). The newly-generated active cation and anion species revealed by Raman, NMR and MS spectra, increase the electrochemical potential window from 1.8 V to 2.8 V vs Mg on stainless steel electrode, rendering electrolytes the ability to examine high voltage cathodes. More importantly, on account of the non-nucleophilicity of active electrolyte species, we present the first example of magnesium-sulfur (Mg-S) batteries using Mg(BH4)2-based electrolytes, which exhibit a high discharge capacity of 955.9 and 526.5 mA h g-1 at the initial and 30th charge/discharge cycles, respectively. These achievements not only provide an efficient and specific strategy to eliminate the major roadblocks facing Mg(BH4)2-based electrolytes but also highlight the profound effect of functional additives on the electrochemical performances of unsatisfied Mg-ion electrolytes.

Pristine and modified radix Angelicae dahuricae (Baizhi) residue for the adsorption of methylene blue from aqueous solution: A comparative study

In the present study, samples derived from radix Angelicae dahuricae (Baizhi, BZ) residue, a traditional Chinese herb, were investigated for their adsorption behavior and mechanism of methylene blue (MB). Optimization of factors like SDS impregnation ratio, contact time and pH on the adsorption were conducted firstly and it showed that the highest adsorption capacity of BZ samples when the SDS impregnation ratio equals to 1:1 at pH 10.5 at equilibrium. According to the study on pHpzc and pH, the SDS loading on BZ contributed to reducing the repulsion force between BZ sample and MB molecule and thus promoting the absorption. The adsorption kinetics was found to follow the pseudo-second-order kinetic model, suggesting chemisorption plays the dominant role in the adsorption process. The Langmuir model is adequate to represent the MB adsorption data, the maximum monolayer adsorption capacity (QL) for BZ 11 (SDS impregnation 1:1) was 1411 mg/g. By studying adsorption kinetics and thermodynamics, it is concluded that SDS impregnation increased the adsorption capacity by strengthening the adsorbent-adsorbate bonding force rather than augment the numbers of available active sites. Elemental analysis (EA), fourier transform infrared spectrometry (FT-IR) and scanning electron microscopy (SEM) analysis of BZ samples confirmed the SDS impregnation and the adsorption of MB molecules. Based on experimental results, Brunauer-Emmett-Teller (BET) and FT-IR, it is reckoned that after ring opening under alkaline conditions, the coumarin could produce cis-o-coumaric acid as the strong electron-donating structure which reacted with the strong electron acceptor MB molecule to produce the charge transfer complex and enhanced adsorption. The remarkable adsorption capacity of BZ samples compared to various natural and artificial materials and the high resorption rate as 97.8% indicated the radix Angelicae dahuricae residue as a potential adsorbent material.