High Electron Affinity Research Articles

Inside Cover Picture

Herein, we developed a series of conjugated polymers based on an indandione‐terminated quinoidal unit for the application of organic thermoelectric. Owning to the high electron affinity of the quinoidal unit, all polymers showed low‐lying LUMO energy levels below –4.10 eV. By incorporating electron‐withdrawing substituents (F or CN) on the comonomer, the LUMO energy levels of the polymers can be further downshifted to –4.36 eV. The decreased LUMO level is favorable for a high doping efficiency, thus leading to high electrical conductivity and good thermoelectric performance. Among the synthesized polymers, PIQ‐2CNBT with the deepest LUMO level achieved the best thermoelectric performance with a PF of up to 2.14 μW·m–1·K–2. More details are discussed in the article by Deng et al. on page 776—782.image

Designing covalent organic frameworks with Co-O4 atomic sites for efficient CO2 photoreduction

Cobalt coordinated covalent organic frameworks have attracted increasing interest in the field of CO2 photoreduction to CO, owing to their high electron affinity and predesigned structures. However, achieving high conversion efficiency is challenging since most Co related coordination environments facilitate fast recombination of photogenerated electron-hole pairs. Here, we design two kinds of Co-COF catalysts with oxygen coordinated Co atoms and find that after tuning of coordination environment, the reported Co framework catalyst with Co-O4 sites exhibits a high CO production rate of 18000 µmol g−1 h−1 with selectivity as high as 95.7% under visible light irradiation. From in/ex-situ spectral characterizations and theoretical calculations, it is revealed that the predesigned Co-O4 sites significantly facilitate the carrier migration in framework matrixes and inhibit the recombination of photogenerated electron-hole pairs in the photocatalytic process. This work opens a way for the design of high-performance catalysts for CO2 photoreduction.

Non-Fullerene Electron Acceptors Based on Hybridisation of Corannulene and Thiophene-S,S-Dioxide Motifs.

Herein we show that hybridisation of buckybowl corannulene and thiophene-S,S-dioxide motifs is a general approach for the preparation of high electron affinity molecular materials. The devised synthesis is modular and relies on thienannulation of corannnulene-based phenylacetylene scaffolds. The final compounds are highly soluble in common organic solvents. These compounds also exhibit interesting optical properties such as absorption and emission in the blue/green regions of the electromagnetic spectrum. Importantly, a bis-S,S-dioxide derivative exhibits three reversible reductions similar in their strength to the prevalent fullerene-based electron acceptor phenyl-C61 -butyric acid methyl ester (PC61 BM).

Prediction of stable radon fluoride molecules and geometry optimization using first-principles calculations

Noble gases possess extremely low reactivity because their valence shells are closed. However, previous studies have suggested that these gases can form molecules when they combine with other elements with high electron affinity, such as fluorine. Radon is a naturally occurring radioactive noble gas, and the formation of radon-fluorine molecules is of significant interest owing to its potential application in future technologies that address environmental radioactivity. Nevertheless, because all isotopes of radon are radioactive and the longest radon half-life is only 3.82 days, experiments on radon chemistry have been limited. Here, we study the formation of radon molecules using first-principles calculations; additionally, possible compositions of radon fluorides are predicted using a crystal structure prediction approach. Similar to xenon fluorides, di-, tetra-, and hexafluorides are found to be stabilized. Coupled-cluster calculations reveal that RnF6 stabilizes with Oh point symmetry, unlike XeF6 with C3v symmetry. Moreover, we provide the vibrational spectra of our predicted radon fluorides as a reference. The molecular stability of radon di-, tetra-, and hexafluoride obtained through calculations may lead to advances in radon chemistry.

Enhanced n‐Type Thermoelectric Performance of Conjugated Polymers Based on an Indandione‐Terminated Quinoidal Unit through Comonomer Optimization

Comprehensive SummaryConjugated polymers (CPs) containing quinoidal units are promising in n‐type organic thermoelectric materials because of their deep‐positioned lowest unoccupied molecular orbital (LUMO) energy levels and planar conjugated backbones. Herein, three CPs have been synthesized by copolymerizing an indandione‐terminated quinoidal unit with bithiophene derivatives. Owning to the high electron affinity of the indandione‐terminated quinoidal unit, all polymers showed deep LUMO energy levels below –4.10 eV. Incorporating electron‐withdrawing substituents (F or CN) on the bithiophene comonomer can further downshift the LUMO energy levels. As a result, a more efficient n‐doping process can be realized when employing 4‐(2,3‐dihydro‐1,3‐dimethyl‐1H‐benzimidazol‐2‐ yl)‐N,N‐dimethylbenzenamine (N‐DMBI) as the dopant. Ultimately, the polymer with CN substituents delivered the best thermoelectric performance with a power factor of up to 2.14 μW·m−1·K−2, because it possessed the lowest LUMO energy level among the three CPs. This work highlights that the modulation of LUMO energy level is an effective strategy to optimize the thermoelectric performance of CPs.

Unlocking the Full Potential of Electron-Acceptor Molecules for Efficient and Stable Hole Injection.

Understanding the hole-injection mechanism and improving the hole-injection property are of pivotal importance in the future development of organic optoelectronic devices. Electron-acceptor molecules with high electron affinity (EA) are widely used in electronic applications, such as hole injection and p-doping. Although p-doping has generally been studied in terms of matching the ionization energy (IE) of organic semiconductors with the EA of acceptor molecules, little is known about the effect of the EA of acceptor molecules on the hole-injection property. In this work, the hole-injection mechanism in devices is completely clarified, and a strategy to optimize the hole-injection property of the acceptor molecule is developed. Efficient and stable hole injection is found to be possible even into materials with IEs as high as 5.8 eV by controlling the charged state of an acceptor molecule with an EA of about 5.0eV. This excellent hole-injection property enables direct hole injection into an emitting layer, realizing a pure blue organic light-emitting diode with an extraordinarily low turn-on voltage of 2.67V, a power efficiency of 29lm W-1 , an external quantum efficiency of 28% and a Commission Internationale de l'Eclairage y coordinate of less than 0.10.

Double [4]Helicene-like Naphthobisbenzothiophene Diimides and Their Thienyl-S,S-dioxidized Derivatives with Attractive Solid-State Fluorescence and High Electron Affinity

A series of double [4]helicene-like naphthobisbenzothiophene diimides and their thienyl-S,S-dioxidized derivatives are synthesized via MoCl5-catalyzed cyclization and m-CPBA-mediated oxidation reactions. The functional five-membered ring diimides show a helicene-like geometry, strong solid-state fluorescence, and deep LUMO of -4.37 eV.

Ambipolar charge transport in a non-fullerene acceptor

Charge transport is one of the key factors in the operation of organic solar cells. Here, we investigate the electron and hole transport in the non-fullerene acceptor (NFA) IT-4F, by a combination of space-charge-limited current measurements and multiscale molecular simulations. The electron and hole mobilities are fairly balanced, amounting to 2.9 × 10−4 cm2 V−1 s−1 for electrons and 2.0 × 10−5 cm2 V−1 s−1 for holes. Orientational ordering and electronic couplings facilitate a better charge-percolating network for electrons than for holes, while ambipolarity itself is due to sufficiently high electron affinity and low ionization energy typical for narrow-gap NFAs. Our findings provide a molecular-level understanding of the balanced hole and electron transport in an archetypical NFA, which may play a key role in exciton diffusion and photogenerated hole transfer in organic solar cells.

Sunlight Bleaching of Subporphyrazine Dye Films

Stable subphthalocyanine-type dyes with a high electron affinity attract much attention as potential substitutes for traditional fullerenes in molecular electronics devices. One possible way to enhance the acceptor properties of the subphthalocyanine core is by replacing the peripheral benzene fragments (C6H4) with 1,2,5-thiadiazole fragments (C2N2S1). However, the resistance of these materials to light or atmospheric effect remains an open question, which limits their further application in device manufacturing. In this work, we compare vacuum-deposited films of three derivatives, SubPzS3H0 (all peripheral fragments are 1,2,5-thiadiazoles), SubPzS2H4 (two fragments are 1,2,5-thiadiazoles and one fragment is benzene), and SubPcS0H12 (all benzenes, i.e., parent subphthalocyanine). Practically relevant substrates were used for deposition, namely, bare glass, glass/ITO or FTO, and PET/ITO. Photobleaching of films under continuous 1 sun illumination was studied in laboratory air, synthetic air, and ultrapure argon. It is shown that the exclusion of near-UV photons from the incident light spectrum, which corresponds to the absorption of subphthalocyanines in the Soret-band, strongly inhibits degradation. Absorption in the Q-band range initiates soft annealing rather than photobleaching of films. The stability of the films deposited on glass decreases as SubPzS3H0 > SubPzS2H4 > SubPcS0H12 in air, and vice versa in argon. The substrate adds more complexity to this picture. In argon, the ITO coating reduces degradation of all of the compounds equally, in contrast to the glass samples, while in air, the SubPzS3H0 films discolor completely. The latter reaction proceeds due to the indium-containing species migrating from the conductive coating.

Intermediate nanofibrous charge trapping layer-based wearable triboelectric self-powered sensor for human activity recognition and user identification

Significant research has been conducted to find practical methods to increase the triboelectric charge density of friction surfaces and improve the TENG output performance. In this study, a double-layer nanofibrous-TENG is newly proposed, consisting of MXene/P(VDF-TrFE) as a charge-generating layer and Siloxene/cobalt-nanoporous carbon/P(VDF-TrFE) as a charge-trapping layer, fabricated via a facile electrospinning process. The charge-generating layer generates abundant surface charges owing to the high electronegativity and electron affinity of MXene. Similarly, Siloxene as a filler in the charge-trapping layer improves the dielectric property of the layer, whereas hierarchically porous structure with a large surface area of cobalt nanoporous carbon provides more active sites for charge storage. After utilizing the charge-trapping layer, the current density and surface potential of the double-layer nanofibrous TENG is two-fold higher than the single-layer nanofibrous TENG. Furthermore, the TENG with Nylon 6/6 nanofiber as a positive friction layer, delivers a power density of 19 W m-2, which shows superior output performance compared to the state-of-the-art works. Finally, the fabricated device is attached to the shoe insole, and the triboelectric sensor data is analyzed using cutting-edge deep learning technology, which exhibited an accuracy of 99% in user identification and user activity recognition. Thus, this study investigates the possibilities of using the electrospun double-layer nanofibrous mat to boost the TENG output performance and explores its applications in artificial intelligence and human activity recognition systems.

Nanostructured doping of WSe2via block copolymer patterns and its self-powered photodetector application.

Transition metal dichalcogenides (TMDs), e.g., MoS2, MoSe2, ReS2, and WSe2, are effective materials for advanced optoelectronics owing to their intriguing optical, structural, and electrical properties. Various approaches for manipulating the surface of the TMDs have been suggested to unleash the optoelectronic potential of the TMDs. Herein, we employed the self-assembly of the poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer (BCP) to prepare a nanoporous pattern and generate nanostructured charge-transfer p-doping on the WSe2 surface, maximizing the depletion region in the absorber layer. After the spin coating and thermal annealing of PS-b-PMMA, followed by the selective etching of PMMA cylindrical microdomains using oxygen reactive-ion plasma, nanopatterned WOx with high electron affinity was grown on the WSe2 surface, forming a three-dimensional homojunction. The nanopatterned WOx significantly expanded the depletion region in the WSe2 layer, thus enhancing optoelectronic performance and self-powered photodetection. The proposed approach based on the nanostructured doping of the TMDs via BCP nanolithography can help create a promising platform for highly functional optoelectrical devices.

Recent progress on the design and applications of superhalogens.

The research on superhalogens has successfully completed four decades. After their prediction in 1981 and experimental verification in 1999, such species have attracted attention due to their unusual structures and intriguing applications. Superhalogens are species whose electron affinity exceeds that of halogen or whose anions possess a larger vertical detachment energy than that of halides. Initially, these species were designed using s and p block atoms having a central electropositive atom as the core with excess electronegative atoms as ligands such as F, Cl, O etc. The last decade has witnessed enormous progress in the field of superhalogens. The transition metal atoms have played the role of the central core and a variety of new ligands have been explored. Further, new classes of superhalogens such as polynuclear superhalogens, magnetic superhalogens, aromatic superhalogens, etc. have been reported. The first application of superhalogens as strong oxidizers appeared much before their conceptualization. In the last decade, however, their applications have spanned a variety of fields such as energy storage, superacids, organic superconductors, ionic liquids, liquid crystals, etc. This makes research in the field of superhalogens truly interdisciplinary. This article is intended to highlight the progress on the design and applications of superhalogens in the last decade.

Reduction of copper from oxides when heated in air

The paper presents the results of experiments on the reduction of copper oxides formed during the heat treatment of metallic copper samples in air. The necessary condition is the presence of a muffle made of a material with a higher electron affinity (lower standard electrode potential) compared to copper. Replacing nitrogen in the composition of the atmosphere with an equal proportion of argon does not change the observed redox pattern. Our results indicate an electrochemical mechanism for the reduction of copper oxides in a steel muffle, in which oxygen plays the role of a charge carrier. Keywords: oxidation of metallic copper, reduction of copper oxides, steel muffle, air, oxygen, electrochemistry.

Восстановление меди из оксидов при нагревании в воздухе

The paper presents the results of experiments on the reduction of copper oxides formed during the heat treatment of metallic copper samples in air. A necessary condition is the presence of a muffle made of a material with a higher electron affinity (lower standard electrode potential) compared to copper. Replacing nitrogen in the composition of the atmosphere with an equal proportion of argon does not change the observed redox pattern. Our results indicate an electrochemical mechanism for the reduction of copper oxides in a steel muffle, in which oxygen plays the role of a charge carrier.

Superior high-temperature capacitive performance of polyaryl ether ketone copolymer composites enabled by interfacial engineered charge traps.

Metalized film capacitors with high-temperature capacitive performance are crucial components in contemporary electromagnetic energy systems. However, the fabrication of polymer-based dielectric composites with designed structures faces the challenge of balancing high energy density (Ue) and low energy loss induced by electric field distortion at the interfaces. Here, BN nanoparticles coated with a thin layer of aminobenzoic acid (ABA) voltage stabilizer are introduced into a copolymer of aryletherketone and 2,6-bis(2-benzimidazolyl)pyridine (P(AEK-BBP)). Our results demonstrate that the ABA voltage stabilizer, possessing high electron affinity, significantly improves the dispersion of BN particles within the matrix, mitigates electric field distortion, and creates effective charge traps. This, in turn, effectively suppresses high-temperature-induced Schottky emission and P-F emission, leading to a dramatic decrease in leakage loss. As a result, the optimized composite film, filled with 0.3 vol% m-ABA-BN particles, exhibites a Ue of 10.1 J cm-3 and a η of 90% at 150 °C and 600 MV m-1, surpassing the majority of previously reported materials. Furthermore, even after undergoing 100 000 cycles at 150 °C and 250 MV m-1, the composite dielectric films demonstrate favorable charge-discharge characteristics. This work offers a novel approach to fabricate polymer-based dielectric materials with high-temperature resistance and high discharging efficiency for long-term high energy storage applications.

국내 수송환경에 적합한 마찰전기 나노발전기의 발전특성 분석

Sustainable energy supplies without the recharging and replacement of charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications. The TENG harvests electrical energy from wasted mechanical energy in the ambient environment. TENG devices are very likely to be used in next-generation renewable energy and energy harvesting. TENG devices have the advantage of being able to manufacture very simple power devices. In this experiment, various organic dielectrics and inorganic dielectrics were used to improve the open voltage of TENG, Among the various organic dielectrics, Teflon-based FEP, which has the highest electron affinity, showed the highest open voltage and Al electrode was fabricated on Teflon substrate by sputtering deposition process. And AAO (Anodized Aluminum Oxide) nanostructures were applied to maximize the specific surface area of the TENG device. The power generation of TENG within the acceleration level (0.25, 0.5, 1.0, 1.5 and 2 G) and the frequency range (5-120 Hz) of the domestic transport environment was up to 4 V.

Acceleration Effect of Bowl-Shaped Structure in Aerobic Oxidation Reaction: Synthesis of Homosumanene ortho-Quinone and Azaacene-Fused Homosumanenes.

An oxidation reaction of hydroxyhomosumanene on silica gel providing homosumanene ortho-quinone and its synthetic application for azaacene-fused homosumanenes is described. Hydroxyhomosumanene is photochemically oxidized by air, when it is coated on silica gel; this aerobic oxidation proceeds faster than that of planar analogues. The difference of such reactivity was attributed to the unusual keto-enol tautomerization due to structural difference between planar and curved π-system. The homosumanene ortho-quinone was used in the synthesis of several azaacene-fused homosumanenes, azaacenohomosumanenes. X-ray diffraction analysis of the single crystals revealed their columnar stacking structures due to the interactions between each bowl. Azaacenohomosumanenes exhibited high electron affinity due to the combination of buckybowl and electron-deficient azaacene moieties.

Pristine, carboxylated, and hybrid multi-walled carbon nanotubes exert potent antioxidant activities in in vitro-cell free systems

Multi-walled carbon nanotubes (MWCNTs) are tubular-shaped carbon allotropes, composed of multiple concentric graphene cylinders. The extended systems of conjugated double bonds, that MWCNTs are constituted by, provide them with high electron affinities, enabling them to act as electron donors or acceptors. Consequently, their potential biomedical applications, as synthetic antioxidant agents, are of particular interest. Based on the above, the purpose of the present study was to evaluate the intrinsic antioxidant properties of pristine and carboxylated MWCNTs, as well as of novel hybrid nanocomposites of MWCNTs and inorganic nanoparticles. To this end, after the synthesis and characterization of MWCNTs, their antiradical, reducing, and antigenotoxic properties were assessed in cell-free assays, using a methodological approach that has been recently proposed by our research group. According to our results, most of the tested MWCNTs exhibited strong antioxidant activities. More elaborately, the hybrid material of MWCNTs and ferrous oxide nanoparticles, i.e., CNTs@Fe3O4, showed robust scavenging capacities in all free-radical scavenging assays examined. As regards reducing properties, the pristine MWCNTs, i.e., CNTs-Ref, exhibited the greater electron donating capacity. Finally, in terms of antigenotoxic properties, the hybrid material of MWCNTs and silicon carbide nanoparticles, i.e., CNTs@SiC, exhibited potent ability to inhibit the formation of peroxyl radicals, thus preventing from the oxidative DNA damage. Conclusively, our findings suggest that the MWCNTs of the study could be considered as promising broad-spectrum antioxidants, however, further investigations are required to evaluate their toxicological profile in cell-based and in vivo systems.

Orbital Mixing between Colloidal Quantum Dots and Surface-Bound Molecules

Orbital mixing is paramount to chemistry as it plays a central role in bond formation. It is also important for technologies such as molecular doping of polymers, where the concept of fractional charge transfer is essentially orbital mixing between dopants and hosts. Likewise, it would be both fundamentally interesting and technologically relevant to investigate orbital mixing in emerging hybrid materials containing both inorganic and organic moieties. Here we report experimental observation of orbital mixing between valence band levels of strongly confined PbS quantum dots (QDs) and lowest unoccupied molecular levels of surface-bound high-electron affinity molecules (F4TCNQ), manifested as both an absorption blue-shift of PbS and the emergence of visible and infrared signatures of the fractional charge-transfer species of F4TCNQ. The degree of mixing can be controlled by varying the QD size or by varying the molecule/QD ratio for a specific QD size and can be quantitatively reproduced by a nondegenerate, two-level perturbation model.

Optimization of thermoelectric performances of conjugated polymers containing Trans-1,2-di(2-thienyl)ethylene subunits via structural modulation and doping engineering

Focusing on the thermoelectric (TE) properties of (E)-1,2-di(thiophen-2-yl)ethene (TVT)-based organic conjugated polymers, backbone modification via copolymerization with different subunits and chemical doping with variant dopants are implemented. Herein, two polymers named PTVTTT14 and PTVTDTT18 with subtle structural difference are synthesized by copolymerizing TVT with TT (thieno[3,2- b ]thiophene) and DTT (dithieno[3,2-b:2′,3′-d]thiophene), respectively. Cooperation with less extended fused thiophene units TT, PTVTTT14 displays better solubility and hence larger molecular weight even with shortening alkyl side-chains comparing to that of PTVTDTT18. All these factors facilitate its better thermoelectric conversion efficiency. Furthermore, three dopants (CuTFSI, CN 6 CP and F 4 TCNQ) were employed to optimize polymers' TE performances. PTVTTT14 and PTVTDTT18 display highest PF of 9.4 and 5.0 μW m −1 K −2 with F 4 TCNQ as dopant. The higher electron affinity (EA) of F 4 TCNQ and CN 6 CP than ionization energy (IE) of the two polymers is energetically favorable to charge transfer, but the poor solubility of CN 6 CP hindering its effective doping. Moreover, CuTFSI-doped polymers show highest conductivity but lowest Seebeck coefficient ( S ) and power factor (PF) on account of its strong doping ability. Prospectively, reasonable ideas for polymers design and dopants selection are provided to obtain TVT-based polymers with better TE properties. • Correlation between structure and thermoelectric performances of TVT-based polymers was investigated. • By reducing a thiophene unit of conjugated backbone and shortening the alkyl side-chain, doped PTVTTT14 performed better thermoelectric performances than doped PTVTDTT18. • Optimized PF of PTVTTT14 and PTVTDTT18 were obtained upon F 4 TCNQ doping via doping engineering. • Selecting dopants with well matched energy level well with polymers are critical for optimization of the thermoelectric performances.