Electron Donor Molecules Research Articles

Theoretical study on the charge transport and metallic conducting properties in organic complexes.

The charge transfer process between substrate molecular and dopant always appears in doped organic semiconductors, so that molecular doping is a common method to improve the electrical properties by combining appropriate complexes of electron acceptor and donor molecules. At the interface of the doped complexes, the amount of charge-transfer based on the charge analysis method could be affected by various factors, including the stacking structure, the HOMOD-LUMOA gaps, the offset defined by the donor ionization potential and the acceptor electron affinity IPD-|EAA|, and the strength of the intermolecular orbital interaction. To better understand the charge transport properties in complex crystals, reasonable mobility values were calculated by combining semi-classical Marcus-Hush theory with molecular dynamics simulation, in which the mobility values were on the same order of magnitude as experimental values. The largest and average room-temperature mobility were 4.59 and 0.21 cm2 V-1 s-1 for TTF-TCNQ based on the anisotropic transport properties and random-walk schemes of the charge diffusion coefficient. The interface of the TTF-TCNQ crystal possesses metallic conducting properties with a predicted resistance of 4.43 kΩ. Charge-transfer complexes exhibit larger mobility and higher conductivity compared to the constituent donor and acceptor molecules.

High-Performance Nonfullerene Polymer Solar Cells Based on a Wide-Bandgap Polymer without Extra Treatment.

Nonfullerene polymer solar cells (PSCs) are developed based on a fluorinated thienyl-based wide-bandgap (WBG) polymer PBBF as the electron donor and nonfullerene small molecule IDIC as the electron acceptor. PBBF exhibits a strong absorption in the range of 300-605nm with a wide optical bandgap of 2.05eV, which is complementary with that of IDIC. Meanwhile, it possesses a deeper highest occupied molecular orbital energy level of -5.52eV and a higher hole mobility of 7.3×10-4 cm2 V-1 s-1 compared to the nonfluorinated polymer PBDTT. The PSCs based on PBBF:IDIC without extra treatment show a power conversion efficiency (PCE) of 8.5% with a V oc of 0.95V, a J sc of 15.3mAcm-2 , and an FF of 58.8%, which is much higher than that of the devices based on PBDTT:IDIC (a PCE of 5.3% with a V oc of 0.88V, a J sc of 13.7mAcm-2 , and an FF of 43.9%). These results indicate that PBBF is a promising WBG polymer donor material for the photovoltaic applications in nonfullerene PSCs.

An Organometallic Molecular Wire Bearing a Manganese Porphyrin Linker: Coordination-driven Modulation of the Metal-Metal Interaction

Here, we report synthesis and properties of a di-ruthenium acetylide molecular wire having a diethynylporphyrinatomanganese linker, and the effect of the coordination of electron-donor molecules to...

Alpha-lipoic acid, but not di-hydrolipoic acid, activates Nrf2 response in primary human umbilical-vein endothelial cells and protects against TNF-α induced endothelium dysfunction

The antioxidants role in cell response regulation attracted great interest in the last decades and it is undergoing to a profound reconsideration. The mere concept of “biological antioxidant” has been frequently misconceived or misused, possibly leading to the misinterpretation of some experimental observation. Organosulfur compounds in general and α-lipoic acid, a dithiol molecule, can be considered a typical example of the kind. Reduced α-lipoic acid, dehydrolipoic acid has been in fact originally considered a bona fide, reducing, electron donor molecule. A more recent approach, according to stoichiometric and thermodynamic evidences, lead to a reinterpretation of the biochemical role of “antioxidants”. The electrophilic nature of oxidized nucleophilic molecules, including α-lipoic acid, renders more plausible a mechanism based on the ability to activate Nrf2/EpRE mediated hormetic response.In this study, we demonstrate that nmolar concentrations of oxidized α-lipoic acid, but not dehydrolipoic acid, protect human umbilical primary endothelial cells (HUVEC) from TNF-α induced dysfunction, inhibit NF-κB activation and block apoptosis following the activation of Nrf2 transcription factor. Our observations corroborate the concept that the major, if not the unique, mechanism by which α-lipoic acid can non-enzymatically exert its reducing activity is related to the electrophilic nature of the oxidized form.

Lone-Pair Delocalization Effects within Electron Donor Molecules: The Case of Triphenylamine and Its Thiophene-Analog

Triphenylamine (TPA) and its thiophene-analog, N,N-Diphenyl-2-thiophenamine (DPTA), are both well known as electron-donating molecules implemented in optoelectronic devices such as organic solar ce ...

ZINC(II) BIS(DIPYRROMETENATES) AS NEW FLUORESCENT CHEMOSENSORS OF N- AND O-CONTAINING ANALYTES

The results of spectral studies of the fluorescence of binuclear zinc(II) bis(dipyrrinate)s with 3,3′-, 2,3′- and 2,2′-bis(dipyrrine)s of the composition [Zn2L2] in binary mixtures of cyclohexane and N- and O -containing solvent Х (acetone, DMF, DMSO, TEA) are presented. Spectrophotometric studies have shown that additive in cyclohexane of analyte upto χХ<0.2 leads to red shift (to ~10 nm) of emission band maximum and to a sharp decrease in fluorescence quantum yield (φ) of [Zn2L2] luminophores. The observed effect is due to the additional coordination processes of the electron-donor molecules X, leading to the formation of solvates [Zn2L2Xn]. The efficiency of fluorescence quenching of [Zn2L2], formed by 3,3′, 2,3′- or 2,2′-bis(dipyrrine)s, is different. Zinc(II) 3,3′-bis(dipyrrometenat) demonstrates the highest sensitivity to fluorescence at the presence of X, as compared with the 2,3′- and 2,2′-analogues. The interpretation of found experimentally linear correlations of φ and calculated on the Stern-Volmer model of the apparent quenching fluorescence constants of helicates from the electron-donating ability of the analytes was given. Indicators of intensity relative change at different wavelengths of the [Zn2L2] fluorescence spectrum were suggested as analytical criterion of the analyte identification. The detection limits of toxicants X by means of [Zn2L2] amounted upto ~ 10–7– 10–5 mol/l in organic media. High specificity of spectral-luminescence characteristics changing in the presence of particular N- and O-containing analytes provides the possibility of using [Zn2L2] helicates as new fluorescent selective chemosensors of the electron-donor molecules in liquid media.

Exciplex: An Intermolecular Charge-Transfer Approach for TADF.

Organic materials that display thermally activated delayed fluorescence (TADF) are a striking class of functional materials that have witnessed a booming progress in recent years. In addition to pure TADF emitters achieved by the subtle manipulations of intramolecular charge transfer processes with sophisticated molecular structures, a new class of efficient TADF-based OLEDs with emitting layer formed by blending electron donor and acceptor molecules that involve intermolecular charge transfer have also been fabricated. In contrast to pure TADF materials, the exciplex-based systems can realize small Δ EST (0-0.05 eV) much more easily since the electron and hole are positioned on two different molecules, thereby giving small exchange energy. Consequently, exciplex-based OLEDs have the prospective to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency. Therefore, the challenging issue of achieving small Δ EST in organic systems could be solved. In this article, we summarize and discuss the latest and most significant developments regarding these rapidly evolving functional materials, wherein the majority of the reported exciplex forming systems are categorized into two subgroups, viz. (a) exciplex as TADF emitters and (b) those as hosts for fluorescent, phosphorescent and TADF dopants according to their structural features and applications. The working mechanisms of the direct electroluminescence from the donor/acceptor interface and the exciplex-forming systems as cohost for the realization of high efficiency OLEDs are reviewed and discussed. This article delivers a summary of the current progresses and achievements of exciplex-based researches and points out the future challenges to trigger more research endeavors to this growing field.

Phosphorene quantum dots

Phosphorene, a two-dimensional material, has been a subject of recent investigations. In the present study, we have prepared blue fluorescent phosphorene quantum dots (PQDs) by liquid phase exfoliation of black phosphorus in two non-polar solvents, toluene and mesitylene. The average particle sizes of PQDs decrease from 5.0 to 1.0 nm on increasing the sonicator power from 150 to 225 W. The photoluminescence spectrum of the PQDs is red-shifted in the 395–470 nm range on increasing the excitation-wavelength from 300 to 480 nm. Electron donor and acceptor molecules quench the photoluminescence, with the acceptors showing more marked effects.

Ligand-controlled Behavior of Ag(I)–π Complex as σ-Lewis Acid

Abstract An efficient σ-Lewis acidic Ag(I) complex has been obtained by complexation with an electron-donating π-conjugated molecule as a side-on π ligand. The σ-Lewis acidity is possibly derived from the controlled linear coordination around Ag(I) due to the π ligand. A combination of UV-Vis absorption spectroscopy and X-ray absorption near-edge structure analyses clearly revealed that the complex is formed by π ligand-to-Ag(I) charge-transfer interaction. The σ-Lewis acidity was evaluated by IR spectroscopy using 2,6-dimethyl-γ-pyrone as the σ-Lewis basic molecule.

Simple electron donor molecules based on triphenylamine and carbazole derivatives

Electron donating carbazole and triphenylamine derivatives are widely used in molecular electronic materials and in biological fluorescent or active probes. Novel easy-to access, highly substituted, electron-rich carbazole and triphenylamine compounds were designed, synthesized and characterized in photophysical and electrochemical experiments. These compounds, with an unusual D-π-D-π-D molecular design are based on carbazole and triphenylamine cores, thiophene conjugated linker and donor aromatic extremities. They showed excellent light-absorbing and emitting properties with high fluorescent quantum yield along with low oxidation potential and excellent electron donating properties. Computational calculations complete the experimental data, and enlighten about the redox and photophysical processes.

Effect of Halogenation on the Energetics of Pure and Mixed Phases in Model Organic Semiconductors Composed of Anthradithiophene Derivatives and C60

Halogenation, particularly fluorination, is commonly used to manipulate the energetics, stability, and morphology of organic semiconductors. In the case of organic photovoltaics (OPVs), fluorination of electron donor molecules or polymers at appropriate positions can lead to improved performance. In this contribution, we use ultraviolet photoelectron spectroscopy, external quantum efficiency measurements of charge-transfer (CT) states, and density functional theory calculations to systematically investigate the effects of halogenation on the bulk solid-state energetics of model anthradithiophene (ADT) materials, their interfacial energetics with C60, and the energetics of various ADT:C60 blend compositions. In agreement with previous work, nonhalogenated ADT molecules show higher energy CT states in blends with C60 and lower energy CT states in the ADT/C60 bilayers. However, this trend is reversed in the halogenated ADT/C60 systems, wherein the CT state energies of ADT:C60 blends are lower than those in t...

Photoinduced Intermolecular Electron Transfer Mediated by the Colloidal Tyrosyl Bolaamphiphile Assembly.

The self-assembly of tyrosyl bolaamphiphiles is exploited to create a colloidal protein-like host matrix, upon which sacrificial electron-donor molecules associate to create a photosystem II (PSII) mimetic electron-relay system. This system harnesses the tyrosine phenol groups abundant on the surface of the assemblies to mediate photoinduced intermolecular electron transfer. Compared with the l-tyrosine molecules, the tyrosyl bolaamphiphile assembly facilitates electron transfer from the sacrificial electron donor to the oxidized photosensitizer. The enhanced electron relay is likely to be driven by the host function of the assembly associated with the sacrificial electron donor and by the suppression of the oxidative cross-linking of phenoxyl radicals. The tyrosyl bolaamphiphile assembly is advantageous in the construction of a PSII mimetic system with a protein-like nature and displaying biochemical functions.

Band-Like Carrier Transport at the Single-Crystal Contact Interfaces between 2,5-Difluoro-7,7,8,8-tetracyanoquinodimethane and Electron Donors.

Some heterojunction interfaces formed with molecular solids show metal-like transport behavior. In order to clarify the requirement, interfaces are fabricated by lamination of single-crystal electron-accepting 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane (F2TCNQ) and electron-donating molecules with a wide range of ionization potentials. Carrier injection between the acceptor and donor crystals leads to highly conducting interfaces, some of which exhibited band-like charge transport behaviors. Combinations with weak donors also resulted in interfaces with band-like transport properties. Accordingly, band-like conduction was achieved for interfaces where the donor and acceptor crystals do not have well-matched band energies. The results indicate that the wide range of candidates have great potential for modification of the electronic structure of organic crystals. The present method is expected to enable control of the electronic properties of the interface.

Tunable magnetism and spin-polarized electronic transport in graphene mediated by molecular functionalization of extended defects

We use first-principles simulations to investigate the magnetic and the electronic transport properties of functionalized graphene layers upon the presence of extended linear defects (ELDs). We have considered electron-donor molecules, tetrathiafulvalene (TTF), lying on the graphene sites neighboring the ELD (TTF/ELD). Those molecules bond to the graphene sheet mediated by van der Waals interactions, giving rise to a net (molecule$\ensuremath{\rightarrow}$graphene) charge transfer. The $n$-type doping of graphene, as well as the molecule-graphene interaction, are strengthened by the presence of the ELD. There is a charge density accumulation on the C atoms along the defect sites, promoting the formation of magnetic states in TTF/ELD. We show that such a net magnetization can be modified through an external electric field (${E}_{\text{field}}$). Further electronic transport calculations reveal that the transmission coefficients exhibit a spin anisotropy which can be controlled by the ${E}_{\text{field}}$, and thus showing that TTF/ELD is a quite interesting system to realize tunable spin-polarized electronic currents on graphene.

Three-dimensional directed assembly of organic charge-transfer heterostructure.

Multicomponent crystalline heterostructures are a powerful approach to integrate different functional materials into the ordered structures. Here we describe three-dimensional spherical assembly of binary organic solids that consist of electron donor and acceptor molecules. A mechanistic study of heterostructure formation reveals that the dewetting and drying-mediated assembly processes are responsible for the spherical crystallite formation. The assembled spherical heterostructures are highly tunable, crystalline and chemically stable, exhibiting phase separation controlled optoelectronic behavior. This simple, generalizable three-dimensional assembly can be modified for the formation of ordered functional organic multicomponent heterostructures for emerging applications.

Chemical Doping Effects of Gas Molecules on Black Phosphorus Field-Effect Transistors

Black phosphorus (BP) is a recently rediscovered layered material with outstanding optical and electrical properties. Its large adsorption energy and high surface-to-volume ratio have motivated chemical sensing and doping applications. We analyzed the charge transport properties as BP-based field-effect transistors (FETs) were chemically doped by adsorption of gas molecules. The electron-withdrawing NO2 and the electron-donating NH3 molecules were applied to observe p-doping and n-doping behaviors, respectively, in BP channel layer. Y-function method was used to extract the device parameters, allowing us to elucidate the chemical doping effects of different types of gas molecules in BP FETs. Excellent sensing ability of BP-based devices to gas molecules was also demonstrated. Our results provide a facile method to control the device properties of BP-based FET via the chemical doping.

Nanopore-induced host-guest charge transfer phenomena in a metal-organic framework.

A spontaneous entrapment of electron-donating small guest molecules, including tetrathiafulvalene (TTF) and N,N,N',N'-tetramethyl-1,3-propanediamine (TMPDA), was realized in a structurally flexible metal-organic framework, {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)6}∞ (AQDC = anthraquinone dicarboxylates, DMA = N,N-dimethylacetamide), with electron-accepting anthraquinone groups, generating two MOF guest charge transfer complexes: {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)6(TTF)5} and {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)4(H2O)2(TMPDA)7}. Using a mild impregnation procedure, single crystals of the target complexes were obtained via a crystal-to-crystal conversion, and the crystals were suitable for structural analysis. Single crystal X-ray analysis demonstrated the different arrangements of these intercalated donor molecules: some donor molecules interacted with the anthraquinone groups and formed infinite D-A-A-D stacks, some appeared beside the anthraquinone groups but only formed donor-acceptor pairs, and the remainder of the molecules simply filled the space. The charge transfer between the guests and the framework was spectroscopically confirmed, and the radical densities on the organic species were estimated using magnetic susceptibility measurements. Compared with a solid-state mixture of anthraquinone and donor molecules, the evenly distributed donor molecules in the micropores of the MOF resulted in a "solid solution" state and significantly promoted the degree of charge transfer between donors and acceptors. Such an encapsulation process may be adopted as a new strategy for post-modification of the electronic and magnetic properties of MOFs, as well as for generating new semiconducting charge-transfer complexes.

Spectroscopic, electronic and computational properties of a mixed tetrachalcogenafulvalene and its charge transfer complex

The unexplored electron donor molecule triselenathiafulvalene (TSTF) and its corresponding charge transfer complex with the well-known electron acceptor TCNQ exhibit rich electronic, optical and semiconducting properties.

Synthesis, characterization, DFT and TD-DFT studies of novel carbazole-based copolymer used in high efficient dye-sensitized solar cells

New donor-acceptor based copolymer incorporating carbazole as electron donor molecule and benzothiazole as electron withdrawing one has been designed and synthesized for organic solar cells applications. The synthesis procedure was achieved via a chemical oxydation pathway. Structural modifications were examined using infrared spectroscopy. Then, optical properties were investigated by the means of UV-VIS and photoluminescence measurements. A large red shift was observed in both optical absorption and emission spectra, showing an extension of the conjugation length going from the pristine PVK to the PVK-based copolymer. The experimental analyses were completed by theoretical calculations based on density functional theory (DFT) and time-dependant density functional theory (TD-DFT) methods. Then, Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) levels have been calculated in order to elucidate the intramolecular charge transfer (ICT) between the electron acceptor and the electron donor moieties and to establish the energetic diagrams of PVK and the PVK-based copolymer. All results showed that this copolymer exhibit interesting photophysical properties and shows promising photovoltaic trends.

Analyzing the n-Doping Mechanism of an Air-Stable Small-Molecule Precursor.

Efficient n-doping of organic semiconductors requires electron-donating molecules with small ionization energies, making such n-dopants usually sensitive to degradation under air exposure. A workaround consists in the usage of air-stable precursor molecules containing the actual n-doping species. Here, we systematically analyze the doping mechanism of the small-molecule precursor o-MeO-DMBI-Cl, which releases a highly reducing o-MeO-DMBI radical upon thermal evaporation. n-Doping of N,N-bis(fluoren-2-yl)-naphthalene tetracarboxylic diimide yields air-stable and highly conductive films suitable for application as electron transport layer in organic solar cells. By photoelectron spectroscopy, we determine a reduced doping efficiency at high doping concentrations. We attribute this reduction to a change of the precursor decomposition mechanism with rising crucible temperature, yielding an undesired demethylation at high evaporation rates. Our results do not only show the possibility of efficient and air-stable n-doping, but also support the design of novel air-stable precursor molecules of strong n-dopants.