Properties Of Organic Materials Research Articles

ИССЛЕДОВАНИЕ ВЛИЯНИЯ УСЛОВИЙ ИЗГОТОВЛЕНИЯ НА ФОТОПРОВОДИМОСТЬ ГРАНИЦЫ РАЗДЕЛА ДВУХ ПОЛИМЕРНЫХ ПЛЕНОК

The study of optical properties in organic materials requires taking into account a wide range of features of these materials in connection with their sensitivity to external influences and aggressive environment. In this work, we studied the features of the photoconductivity of the interface between two dielectrics (polydiphenylene phthalide (PDP)) manufactured under different conditions. Drying was carried out in air and in vacuum. This study is necessary to determine the features of the manufacturing process and its effect on the photoconductive properties of the interface. Currently, the structure of the polymer / polymer interface has been fairly well studied by various methods, in particular, atomic force microscopy. However, there is a certain difficulty in obtaining repeatable results due to the presence of dilution of the lower PDP film when the upper polymer layer is applied. In this work, the photoconductive properties were studied on the basis of the measurements of the current-voltage characteristics (CVC) and the curves of the growth and relaxation of the photocurrent. Based on the results obtained within the framework of this work, it is possible to draw conclusions about the contribution of the drying method of experimental structures to the photoconductivity of the interface. It is known that oxygen makes a significant contribution to the electrical conductivity of thin PDP films. Earlier, it was shown on this polymer material that the presence of oxygen leads to a decrease in the conductivity of PDP films due to the formation of charge carrier traps. Moreover, when oxygen interacts with fragments of a polymer molecule, a chemical bond does not arise, which leads to a reversible change in electrical conductivity with a change in oxygen concentration. Due to this, the PDP films demonstrate a high stability of the electrophysical characteristics for several years when repeated measurements are carried out in an open atmosphere and at room temperature. It can be argued that the effect on the response of photoconductivity in organic materials, as well as on the relaxation time, can be associated with the presence of oxygen traps in the PDP films, increasing the relaxation time. This result is extremely important from the point of view of the practical application of these structures.

Permittivity Threshold and Thermodynamics of Integer Charge-Transfer Complexation for an Organic Donor–Acceptor Pair

Molecular charge doping involves the formation of donor-acceptor charge-transfer complexes (CTCs) through integer or partial electron transfer; understanding how local chemical environment impacts complexation is important for controlling the properties of organic materials. We present steady-state and temperature-dependent spectroscopic investigations of the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) complexed with the electron donor and hole transport material N,N'-diphenyl-N,N'-di-p-tolylbenzene-1,4-diamine (MPDA). Equilibrium formation constants (KCT) were determined for donor-acceptor pairs dissolved in a series of solvents covering a range of values of permittivity. A threshold for highly favorable complex formation was observed to occur at ϵ ∼ 8-9, with large (>104) and small (<103) values of KCT obtained in solvents of higher and lower permittivity, respectively, but with chloroform (ϵ = 4.81) exhibiting an anomalously high formation constant. Temperature-dependent formation constants were determined in order to evaluate the thermodynamics of complex formation. In 1,2-dichloroethane (ϵ = 10.36) and chlorobenzene (ϵ = 5.62), complex formation is both enthalpically and entropically favorable, with higher enthalpic and entropic stabilization in the solvent with higher permittivity. Complexation in chloroform is exothermic and entropically disfavored, indicating that specific, inner-shell solvent-solute interactions stabilize the charge-separated complex and result in a net increase in local solution structure. Our results provide insight into how modification to the chemical environment may be utilized to support stable integer charge transfer for molecular doping applications and requiring only modest changes in local permittivity.

Significant Improvement of Solid‐State One‐/Two‐Photon Excited Luminescence in HOFs via Constructing Hydrogen‐Bonded Solvate Model

AbstractA hydrogen‐bonded solvate (HBS) model is herein proposed to construct hydrogen‐bonded organic frameworks (HOFs), for enhancing the solid‐state one‐/two‐photon excited fluorescence (1/2PEF) of organic fluorophores. Two photonic HOFs (ZJU‐HOF‐25 and ZJU‐HOF‐26) are synthesized by using the same organic fluorophore and the fluorophore in them features similar arrangement. The most obvious structural distinction between the two HOFs is the existence of solvent molecules in the crystal cell of ZJU‐HOF‐25. ZJU‐HOF‐25 is regarded as an ideal HBS material where solvent molecules separate fluorophores apart just like dissolving them. But ZJU‐HOF‐26 contains no solvent molecules and the fluorophores are connected directly via hydrogen bonds among them. A significant quantum yield (η) increase is realized from amorphous fluorophores (η ≈0%) to HBS‐based ZJU‐HOF‐25 (η ≈21.75%), while ZJU‐HOF‐26 displays poor 1PEF (η ≈0%). ZJU‐HOF‐25 also exhibits much stronger 2PEF with the two‐photon action cross section larger than ZJU‐HOF‐26 by almost two orders of magnitude. These phenomena are mainly attributed to that the solvent molecules in ZJU‐HOF‐25 benefit the homogeneous separation and conformation fixation of fluorophores, suppressing the non‐radiative transition. The HBS model thus shows the fantastic validity to improve solid‐state optical properties of organic materials, providing guidance for exploring advanced optical materials.

Disilane-bridged architectures: an emerging class of molecular materials.

Disilanes are organosilicon compounds that contain saturated Si-Si bonds. The structural characteristics of Si-Si single bonds resemble those of C-C single bonds, but their electronic structure is more similar to that of C[double bond, length as m-dash]C double bonds, as Si-Si bonds have a higher HOMO energy level. These organosilicon compounds feature unique intramolecular σ electron delocalization, low ionization potentials, polarizable electronic structure, and σ-π interaction. It has been demonstrated that the employment of disilane units (Si-Si) is a versatile and effective approach for finely adjusting the photophysical properties of organic materials in both solution and solid states. In this review, we present and discuss the structure, properties, and relationships of novel σ-π-conjugated hybrid architectures with saturated Si-Si σ bonds. The application of disilane-bridged σ-conjugated compounds as optoelectronic materials, multifunctional solid-state emitters, CPL, and non-linear optical and stimuli-responsive materials is also reviewed.

Conjugated Azo Compounds as Active Materials for Rechargeable Sodium‐Metal Batteries with High‐Rate Performance

AbstractOrganic electrode materials have gained growing attention in the field of sodium‐metal batteries due to their rich reserves, flexibility, and environmental friendliness. However, organic small molecules suffer from poor stability in the electrolyte leading to the decay of battery capacity and reduced cycle life. To address these issues, we report a linear polymer p‐PADA with N=N and C=N as active centers. Its highly‐conjugated and polymerized structure endows the p‐PADA electrode stability, faster reaction kinetics, and exceptional rate performance. When the current density reaches 5 A g−1, p‐PADA still exhibits a specific capacity of 313 mAh g−1 after 1000 cycles. This work demonstrates that polymerization is an effective method to enhance the electrochemical properties of organic materials.

Organic Materials for Electronic and Thermoelectric Applications

Abstract In this invited review article, we give a comprehensive account of the existing literature on the electronic properties of organic materials. The main focus of this article is the rich and extensive literature on the electronic transport in organic materials, particularly conjugated polymers, as they offer numerous advantages over inorganic materials. Consequently, they have found widespread application in photovoltaics, light-emitting displays, and even, more recently, in thermoelectric energy conversion. This literature review will be useful to researchers starting in the field of organic electronics as well as experts seeking to broaden their understanding of transport in polymers.

Establishing patterns of nitrogen application for fire safety of sunflower grain storage facilities

The issue of using nitrogen to eliminate fires in granaries is related to ventilating the grain mass with nitrogen while it is necessary to take into consideration the change in gas concentration. Therefore, the object of this research was the value of the minimum concentration of nitrogen to eliminate the combustion of sunflower grain. It has been proven that in the process of thermal destruction of sunflower grain, the composition of gaseous products of thermal destruction of sunflower grain contains more than 70 % of combustible gases. Namely: carbon monoxide, over 51 %; hydrogen, about 5.7 %; and hydrocarbons with a total concentration of 13.72 %, which provide fire hazardous properties of organic material. Therefore, it should be noted that the release of the amount of combustible gases during pyrolysis requires a reduction in the amount of oxygen in the gas-air environment to eliminate fire sites. Obviously, such a mechanism for the decomposition of sunflower grain during pyrolysis is a factor in regulating the extinguishing process, due to which the amount of nitrogen to eliminate combustion increases. Comparison of experimental studies on the composition of gaseous products of thermal destruction of sunflower grain and studies to determine the minimum fire extinguishing concentration of nitrogen, at which combustion was stopped, made it possible to justify the use of nitrogen. Based on the study's results on the elimination with nitrogen of fire sites of sunflower grain, the values of the minimum fire extinguishing concentration were revealed at extinguishing, about 33.7 % by volume. At the same time, terminating the combustion of sunflower grain occurs with a decrease in the concentration of oxygen in the gas-air environment of about 14 %. The practical significance is the fact that the results obtained for determining the minimum fire extinguishing concentration of nitrogen make it possible to establish operating conditions for granaries when eliminating fire sites

Pairing nitroxyl radical and phenazine with electron-withdrawing/-donating substituents in “water-in-ionic liquid” for high-voltage aqueous redox flow batteries

Aqueous redox-active organic materials-base electrolytes are sustainable alternatives to vanadium-based electrolyte for redox flow batteries (RFBs) due to the advantages of high ionic conductivity, environmentally benign, safety and low cost. However, the underexplored redox properties of organic materials and the narrow thermodynamic electrolysis window of water (1.23 V) hinder their wide applications. Therefore, seeking suitable organic redox couples and aqueous electrolytes with a high output voltage is highly suggested for advancing the aqueous organic RFBs. In this work, the functionalized phenazine and nitroxyl radical with electron-donating and electron-withdrawing group exhibit redox potential of −0.88 V and 0.78 V vs. Ag, respectively, in “water-in-ionic liquid” supporting electrolytes. Raman spectra reveal that the activity of water is largely suppressed in “water-in-ionic liquid” due to the enhanced hydrogen bond interactions between ionic liquid and water, enabling an electrochemical stability window above 3 V. “Water-in-ionic liquid” supporting electrolytes help to shift redox potential of nitroxyl radical and enable the redox activity of functionalized phenazine. The assembled aqueous RFB allows a theoretical cell voltage of 1.66 V and shows a practical discharge voltage of 1.5 V in the “water-in-ionic liquid” electrolytes. Meanwhile, capacity retention of 99.91% per cycle is achieved over 500 charge/discharge cycles. A power density of 112 mW cm−2 is obtained at a current density of 30 mA cm−2. This work highlights the importance of rationally combining supporting electrolytes and organic molecules to achieve high-voltage aqueous RFBs.

Functional Organic Materials for Photovoltaics: The Synthesis as a Tool for Managing Properties for Solid State Applications.

The continuous increase in the global energy demand deeply impacts the environment. Consequently, the research is moving towards more sustainable forms of energy production, storage and saving. Suitable technologies and materials are fundamental to win the challenge towards a greener and more eco-friendly society. Organic π-conjugated materials, including small molecules, oligomers and polymers are a wide and versatile class of functional materials with great potentiality, as they can be used as active matrixes in the fabrication of lightweight, flexible, cheap and large area devices. Their chemical and physical properties, both at a molecular level and mainly in the solid state, are a result of many factors, strictly related to the conjugated structure and functional groups on the backbone, which control the intermolecular forces driving solid state aggregations. The synthesis, through the molecular design, the choice of conjugated backbone and functionalization, represents the first and most powerful tool for finely tuning the chemico-physical properties of organic materials tailored for specific applications. In the present review, we report an overview of our works focused on synthetic methodologies, characterization, structure-properties correlation studies and applications of organic materials designed for energy-involving solid-state applications, organic photovoltaics in particular. The impact of functionalization on electro-optical properties and performance in device are discussed, also in relation to the specific applications.

Discriminating Chiral Supramolecular Motions by Circularly Polarized Luminescence.

Molecular motions are closely associated with the behaviors and properties of organic materials. However, monitoring molecular motions is challenging. Herein, a chiral supramolecular system consisting of L-/D-phenylalanine (LPF/DPF) as a chiral inducer and an achiral tetraphenylethene derivative (TPEF) as a molecular rotor has been proposed and explored for real-time discriminating the supramolecular motions by the visualization of circularly polarized luminescence (CPL) signal variations. Derived from the ordered molecular motions of TPEF induced by LPF/DPF, highly organized aggregates have been progressively assembled in a controlled manner with differentiated morphologies, including spherical particles, one-dimensional fibers, and floor-shaped supercrystals. Notably, increasing level of ordered aggregates, in turn, led to quenching emissions, while the CPL signals have been dramatically amplified accompanying by a sharp enhancement of luminescence dissymmetry factors (glum ) from nearly 0 to -0.1. The significant amplification of CPL is attributed to the ordered aggregates of supramolecules, leading to the decrease of electric transition dipole moments in supramolecular system. As a result of the chiral supramolecular motions powered by supramolecular crystallization, the supramolecular motions are conveniently discriminated by visual CPL signal variation with an enhancement of glum value from 0 to -0.1 in real time.

TCNQ-based organic cocrystal integrated red emission and n-type charge transport

Simultaneously realizing the optical and electrical properties of organic materials is always challenging. Herein, a convenient and promising strategy for designing organic materials with integrated optoelectronic properties based on cocrystal engineering has been put forward. By selecting the fluorene (Flu) and the 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) as functional constituents, the Flu-TCNQ cocrystal prepared shows deep red emission at 702 nm, which is comparable to the commercialized red quantum dot. The highest electron mobility of organic field-effect transistor (OFET) based on Flu-TCNQ is 0.32 cm2 V−1 s−1. Spectroscopic analysis indicates that the intermolecular driving force contributing to the co-assembly of Flu-TCNQ is mainly charge transfer (CT) interaction, which leads to its different optoelectronic properties from constituents.Graphical

Bistable Organic Materials in Optoelectrical Switches: Two-Electrode Devices vs Organic Field Effect Transistors

We present a short overview of research into properties of organic materials and structures that could be used in optoelectrical switches, i.e., switches in which changes in electrical properties are triggered by light of appropriate wavelengths. In particular, we describe the structures acting by virtue of reversible photochemical reactions occurring in photochromic molecular materials.

Synergistic effects of side-functionalization and aza-substitution on the charge transport and optical properties of perylene-based organic materials: a DFT study

The physicochemical properties of organic materials are subject to the chemical structure of the molecular unit and the arrangement of molecules in a crystal.

Tunable uniaxial, area, and volume negative thermal expansion in quartz-like and diamond-like metal-organic frameworks.

This paper proposes that it will be an effective way to discover and explore organic negative thermal expansion (NTE) materials based on the specific topologies in inorganic NTE materials. Various NTE behaviors from the uniaxial, area, and volume-NTE can be achieved by adjusting the topology, for instance, quartz-like and diamond-like. Zn(ISN)2 and InH(BDC) metal–organic frameworks (MOFs) with quartz-like topology have been studied by first principles calculations. The calculated area-NTE of Zn(ISN)2 and uniaxial-NTE of InH(BDC) within quasi-harmonic approximation (QHA) agree well with the experimental data. Through the calculation of Grüneisen parameters, it is shown that low-frequency optical phonons appear dominant resulting in their NTE, but the coupling to high-frequency phonons is of greater ultimate importance. The lattice vibrational modes of great contribution to area-NTE of Zn(ISN)2 and uniaxial-NTE of InH(BDC) are analyzed in detail. Also, four MOFs with diamond-like topology are predicted to exhibit volume-NTE behavior. Moreover, it is found that there is a bulk modulus anomaly in some studied MOFs with the quartz-like and diamond-like framework, where the temperature dependence of bulk modulus does not follow the inverse dependence on that of volume. These specific topologies provide key geometric frameworks for various NTE behaviors of MOFs, and meanwhile, the local structure and bond environment in MOFs can lead to abnormal interatomic force, i.e., bulk modulus anomaly. This abnormal elastic property also deserves more attention.

Configuration Interaction Methods to Predictions on Photophysical Properties of Organic Materials

Configuration Interaction Methods to Predictions on Photophysical Properties of Organic Materials

Magnetic behavior in metal-free radical thin films

<h2>Summary</h2> Magnetism in organic materials is very intriguing: the realization of long-range magnetic order in completely metal-free systems combines magnetic moments with useful properties of organic materials. An essential step for applications is the knowledge of the magnetic behavior that, so far, was investigated only in the proximity of light atoms to heavy metals, impurities, or vacancies, and not as an intrinsic property of thin films that are purely organic. Here, we unravel X-ray magnetic circular dichroism at the carbon and nitrogen K-edges in purely organic radical thin films. Our results show that, controlling the preparation, the magnetic behavior is different than in single crystals. Atomistic simulations indicate that the reason for this is the molecular arrangement in the films when compared with that in the single crystal. The tuning of the film magnetic properties by the molecular arrangement is an exciting perspective toward revealing new properties and applications.

Generation-recombination in disordered organic semiconductor: Application to the characterization of traps

The presence of traps in organic semiconductor based electronic devices affects considerably their performances and their stability. The Shockley-Read-Hall (SRH) model is generally used to extract the trap parameters from the experimental results. In this paper, we propose to adapt the SRH formalism to disordered organic semiconductors by considering a hopping transport process and Gaussian distributions for both mobile and trapped carriers. The model is used to extract multiple trap parameters from charge based Deep Level Transient Spectroscopy (Q-DLTS) spectrum. Calculation of the charge transients are given in detail. The model predicts that the activation energy of the trap should not follow an Arrhenius plot on large temperature ranges. Also, the charge transients are no longer exponential when considering Gaussian trap distributions, enlarging the Q-DLTS peaks. The model fits the Q-DLTS spectra measured on organic diodes with a limited number of trap contributions with a good agreement. It is found that an increase of the material rate of disorder reduces the extracted trap energy distances to the LUMO but has no influence on the extracted trap distribution widths. This work shows the importance of considering the specific properties of organic materials to study their properties and their trap distributions. • A trap emission model has been developed for OSCs including hopping transport and Gaussian DOS for free carriers and traps. • Model predictions: the OSC disorder, i.e., to the width of the intrinsic Gaussian DOS, strongly influences the determined trap energies. • The emission model is validated by extracting trap parameters in organic diodes from Q-DLTS measurements.

Untargeted effects in organic exciton-polariton transient spectroscopy: A cautionary tale.

Strong light-matter coupling to form exciton- and vibropolaritons is increasingly touted as a powerful tool to alter the fundamental properties of organic materials. It is proposed that these states and their facile tunability can be used to rewrite molecular potential energy landscapes and redirect photophysical pathways, with applications from catalysis to electronic devices. Crucial to their photophysical properties is the exchange of energy between coherent, bright polaritons and incoherent dark states. One of the most potent tools to explore this interplay is transient absorption/reflectance spectroscopy. Previous studies have revealed unexpectedly long lifetimes of the coherent polariton states, for which there is no theoretical explanation. Applying these transient methods to a series of strong-coupled organic microcavities, we recover similar long-lived spectral effects. Based on transfer-matrix modeling of the transient experiment, we find that virtually the entire photoresponse results from photoexcitation effects other than the generation of polariton states. Our results suggest that the complex optical properties of polaritonic systems make them especially prone to misleading optical signatures and that more challenging high-time-resolution measurements on high-quality microcavities are necessary to uniquely distinguish the coherent polariton dynamics.

Polarization Resolved Optical Excitation of Charge-Transfer Excitons in PEN:PFP Cocrystalline Films: Limits of Nonperiodic Modeling.

Charge-transfer excitons (CTXs) at organic donor/acceptor interfaces are considered important intermediates for charge separation in photovoltaic devices. Crystalline model systems provide microscopic insights into the nature of such states as they enable microscopic structure-property investigations. Here, we use angular-resolved UV/vis absorption spectroscopy to characterize the CTXs of crystalline pentacene:perfluoro-pentacene (PEN:PFP) films allowing determination of the polarization of this state. This analysis is complemented by first-principles many-body calculations, performed on the three-dimensional PEN:PFP cocrystal, which confirm that the lowest-energy excitation is a CTX. Analogous simulations performed on bimolecular clusters are unable to reproduce this state. We ascribe this failure to the lack of long-range interactions and wave function periodicity in these cluster calculations, which appear to remain a valid tool for modeling properties of organic materials ruled by local intermolecular couplings.

Robust organic functional materials by thermally doping with metal oxide

We have investigated the failure mechanism of organic functional materials and organic light-emitting diodes (OLEDs) by annealing at high temperatures. We found that N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB) doped molybdenum oxide and 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene doped cesium carbonate can enhance the thermal stability significantly. The former composite film reveals the ions of NPB, as observed by X-ray photoelectron spectroscopy (XPS), the formation of which shows that NPB receives the electron that Mo loses. Meanwhile, it is stable for the binding energy of the element in the latter composite film from the XPS image. Through the research of carrier-only cells, the observation indicates that the thermal stability of the doped cell is better than that of the undoped cell at high temperatures. The current efficiency of the doped device is only reduced by 12% after annealing at 80℃; meanwhile the lifetime reaching 208 h is the longest among that of the devices. Simultaneously, the undoped device represents a larger decline even of about 30% with the lifetime reaching just 40 h. We assumed that the enhanced heat-resisting properties of organic materials by inorganic doping might be attributed to the decrease of energy barrier and the reduction of the interface charge accumulation phenomenon caused by high temperature. Inorganic doping paves an alternative way to substitute for synthesizing expensive functional materials with high glass transition temperature.