Molecular Orbital Energy Levels Research Articles

BaTiO3-xNy: Highly Basic Oxide Catalyst Exhibiting Coupling of Electrons at Oxygen Vacancies with Substituted Nitride Ions.

The base strength of oxide catalysts is controlled by the electron charge distribution between cations and anions, with unsaturated oxygen ions that have lone pair electrons typically acting as basic sites. Substitution of oxide ions with anions that have different valences, such as nitride and hydride ions, can often generate basic sites. It is plausible that electrons trapped at oxygen vacancy sites could provide increased electron density and shift the highest occupied molecular orbital energy levels of anions upward in the case that the oxygen vacancies couple with surface-substituted anions. The present work demonstrates that high catalytic basicity can be obtained via site-selective doping of anions at face-sharing Ti2O9 dimer sites with oxygen vacancies in BaTiO3-x. This improved basicity stems from the coupling of substituted nitride ions to electrons at oxygen vacancies. The oxynitride BaTiO3-xNy was found to contain nitride ions that have increased electronic charge density on the basis of such interactions. Enhanced surface basicity following doping with nitride ion was also confirmed by CO2 temperature-programmed desorption and infrared spectroscopy in conjunction with the adsorption of CHCl3. The strong Lewis base sites resulting from the formation of the oxynitride evidently facilitated the catalytic activation of C-H bonds to promote Knoevenagel condensation reactions between aldehydes and active methylene compounds with pKa values of up to 28.9.

A Catalytic Electrolyte Additive Modulating Molecular Orbital Energy Levels of Lithium Polysulfides for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have ultrahigh theoretical specific capacity, but the practical application is hindered by the severe shuttle effect and the sluggish redox kinetics of the intermediate lithium polysulfides (LiPSs). Effectively enhancing the conversion kinetics of LiPSs is essential for addressing these issues. Herein, the redox kinetics of LiPSs are effectively improved by introducing 6-azauracil (6-AU) molecules to the organic electrolyte to modulate the molecular orbital energy level of LiPSs. The 6-AU as a soluble catalyst can form complexes with LiPSs via Li-O bonds. These complexes are liable to transform because of the elevated HOMO and the reduced LUMO energy levels as compared to the dissociative LiPSs, resulting in small energy gaps (Egap) and exhibiting stronger redox activity. Benefiting from the rapid conversion kinetics, the shuttling effect of LiPSs is alleviated to a great extent, so that sulfur utilization is improved and the lithium electrode is protected. In addition, the introduction of 6-AU modulates the deposition behavior of Li2S and eases the coverage of the cathode surface by the insulating Li2S layer. The Li-S battery containing 6-AU provides superior capacity retention of 853 mAh g-1 after 150 cycles at 0.2 C and shows remarkable high-rate performance and retains a specific discharge capacity of 855 mAh g-1 at 5 C. This study accelerates the kinetics of Li-S batteries by tuning the HOMO and LUMO energy levels of LiPSs, which opens an avenue for designing functional electrolyte additives.

Engineering Fluorine‐rich Double Protective Layer on Zn Anode for Highly Reversible Aqueous Zinc‐ion Batteries

AbstractThe high thermodynamic instability and side reactions of Zn‐metal anode (ZMA), especially at high current densities, greatly impede the commercialization of aqueous zinc‐ion batteries (AZIBs). Herein, a fluorine‐rich double protective layer strategy is proposed to obtain the high reversibility of AZIBs through the introduction of a versatile tetradecafluorononane‐1,9‐diol (TDFND) additive in aqueous electrolyte. TDFND molecule with large adsorption energy (−1.51 eV) preferentially absorbs on the Zn anode surface to form a Zn(OR)2− (R=−CH2−(CF2)7−CH2−) cross‐linking complex network, which balances space electric field and controls the Zn2+ ion flux, thus enabling the uniform and compact deposition of Zn (002) crystal planes. Meanwhile, TDFND with low Lowest unoccupied molecular orbital (LUMO, 0.10 eV) energy level is priorly decomposed to regulate the interfacial chemistry of ZMA by building a ZnF2‐rich solid electrode/electrolyte interface (SEI) layer. It is found that a 14 nm‐thick SEI layer delivers excellent structural integrity to suppress parasitic reactions by blocking the direct contact of active water and ZMA. Consequently, the Zn electrode exhibits a superior cycling life over 430 h at 10 mA cm−2 and a high average Coulombic efficiency of 99.8 % at 5 mA cm−2. Furthermore, a 68 mAh pouch cell delivers 80.3 % capacity retention for 1000 cycles.

Engineering Fluorine-rich Double Protective Layer on Zn Anode for Highly Reversible Aqueous Zinc-ion Batteries.

The high thermodynamic instability and side reactions of Zn-metal anode (ZMA), especially at high current densities, greatly impede the commercialization of aqueous zinc-ion batteries (AZIBs). Herein, a fluorine-rich double protective layer strategy is proposed to obtain the high reversibility of AZIBs through the introduction of a versatile tetradecafluorononane-1,9-diol (TDFND) additive in aqueous electrolyte. TDFND molecule with large adsorption energy (-1.51 eV) preferentially absorbs on the Zn anode surface to form a Zn(OR)2- (R= -CH2-(CF2)7-CH2-) cross-linking complex network, which balances space electric field and controls the Zn2+ ion flux, thus enabling the uniform and compact deposition of Zn (002) crystal planes. Meanwhile, TDFND with low Lowest unoccupied molecular orbital (LUMO, 0.10 eV) energy level is priorly decomposed to regulate the interfacial chemistry of ZMA by building a ZnF2-rich solid electrode/electrolyte interface (SEI) layer. It is found that a 14 nm-thick SEI layer delivers excellent structural integrity to suppress parasitic reactions by blocking the direct contact of active water and ZMA. Consequently, the Zn electrode exhibits a superior cycling life over 430 h at 10 mA cm-2 and a high average Coulombic efficiency of 99.8% at 5 mA cm-2. Furthermore, a 68 mAh pouch cell delivers 80.3% capacity retention for 1000 cycles.

Effects of p-type dopant on photovoltaic performance of pervoskite solar cells using phthalocyanine-tetrabenzoporphyrin hole transport materials: A combined theoretical and experimental study

We demonstrate effects of p-type dopant on photovoltaic performance of pervoskite solar cells (PSCs) using phthalocyanine (C6PcH2)-tetrabenzoporphyrin (C6TBPH2) hole transport materials (HTMs) by combining theoretical and experimental studies. Although C6PcH2 and C6TBPH2 molecules share a similar chemical structure, the p-type dopant induced oxidation was only observed in C6TBPH2 molecules through emerging absorption peaks at 2.9 eV and shifting energy band diagram. As a result, power conversion efficiencies (PCEs) of PSCs utilizing C6TBPH2 HTM were improved from around 4 to 14 % by adding p-type dopants, but those of PSCs utilizing C6PcH2 HTM were remained at around 4 %. Numerical simulations indicate that the improvement of PCEs (from 5.7 to 21.1 %) of the simulated cells utilizing the C6TBPH2 HTMs with p-type dopants were attributed to increases in the acceptor densities and deepening the highest occupied molecular orbital energy levels rather than increases in the HTM hole mobility of the HTMs. We suggest that those results could be an indicator for fabrication of efficient PSCs utilizing organic HTMs with p-type dopants.

Stable Spiro‐Linked Terfluorenes with Triphenylamine Pendants as Deep Blue Emitters for Solution‐Processed Organic Light‐Emitting Diodes

AbstractHerein, we reported new spiro‐linked terfluorenes (TF1 and TF2) as solution‐processible hole‐transporting‐free deep‐blue fluorescent emitters for simple structured organic light‐emitting diodes (OLEDs). They were designed and synthesized by incorporating triphenylamine pendants into the C9 positions of the spiro‐linked terfluorene, resulting in a criss‐cross configuration of the two terfluorene backbones and a highly bulky molecular geometry from the pendant groups. Consequently, TF1 and TF2 exhibited good quality thin films by spin‐coating, stable deep blue emissions with no unwanted long wavelength emission after prolonged thermal annealing and UV exposure, shallow highest occupied molecular orbital energy levels (−5.36–−5.37 eV), decent hole mobilities (1.09–1.23×10−7 cm2 V−1 s−1), and high thermal stability, and effectively employed as non‐doped emissive layers in the OLEDs. Particularly, TF2‐based solution‐processed OLED displayed a bright deep blue emission with superior EL performance (turn‐on voltage (Von) of 3.4 V, external quantum efficiency (EQEmax) of 3.82 %, and luminance efficiency (LEmax) of 5.22 cd A−1). This outstanding EL performance of the non‐doped solution‐processed deep blue OLED could be attributed to the effective molecular design, and this work presented a new approach for constructing effective blue emitters based on oligofluorenes.

Facile synthesis of anthracene-based derivatives via a magnetically retrievable Fe3O4@SiO2 immobilized selenoether functionalised NHC-Pd(II) heterogenous catalyst: Photophysical, electrochemical and DFT studies of novel 9,10-anthracene based derivatives

A series of anthracene-based derivatives, which are promising candidates for Organic light-emitting diode (OLEDs) applications, have been synthesized through the Suzuki Miyuara cross-coupling reaction of dibromo anthracene and phenylboronic acids derivatives. A magnetically separable heterogeneous catalyst Fe3O4@SiO2@NHC^SePh-Pd(II) was used, and the coupling reaction was investigated under aerobic conditions using water as a green solvent. A very mild approach for the arylation of the 9,10-dibromo anthracene molecules was adopted to harvest a series of highly conjugated anthracene derivatives. The catalyst was reused for up to seven catalytic cycles without much loss in catalytic efficiency. The 55% transformation in the seventh catalytic cycle indicates the catalyst's robustness and high catalytic potential. Necessary photophysical studies were conducted for selected synthesized anthracene-based derivatives, which includes the absorption, emission and cyclic voltammetric studies. Moreover, the thermogravimetric analysis (TGA) was also conducted to check the thermal stability of the compounds. Finally, a Density Functional Theory (DFT) study was conducted, and it revealed that comparing two anthracene derivatives, the Highest occupied molecular orbital (HOMO) and Least unoccupied molecular orbital (LUMO) energy levels, as well as the HOMO-LUMO gap (HLG), differ, with 9-([1,1′-biphenyl]-4-yl)-10-(4-fluorophenyl) anthracene exhibiting a relatively large HLG. The HOMO is localised along the molecule's main axis, while the LUMO is more delocalised on atoms.

Lifetime enhancement in QDLEDs via an electron-blocking hole transport layer

This study investigates the impact of an engineered hole transport layer (HTL) on the stability of electroluminescent quantum dot light-emitting devices (QDLEDs). The 9-Phenyl-3,6-bis(9-phenyl-9Hcarbazol-3-yl)-9H-carbazole (Tris-PCz) HTL, which possesses a shallower lowest unoccupied molecular orbital (LUMO) energy level compared to the widely used 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) HTL, is employed to confine electron overflow toward the HTL. Utilizing the Tris-PCz HTL results in a 20× improvement in the electroluminescence half-life (LT50) of QDLEDs compared with conventional QDLEDs using the CBP HTL. Electric and optoelectronic analyses reveal that the migration of excess electrons toward the HTL is impeded by the up-shifted LUMO level of Tris-PCz, contributing to prolonged operational device stability. Furthermore, the augmented electric field at the QD/Tris-PCz interface, due to accumulated electrons, expedites hole injection rates, leading to better charge injection balance and the confinement of the exciton recombination zone within the QD and thus the device stability enhancement. This study highlights the significant influence of the HTL on QDLED stability and represents one of the longest LT50 for a QDLED based on the conventional core/shell QD structure.

Side-chain engineering of benzotriazole-based polymers as hole transport material enables high-efficiency CsPbI2Br single-junction and tandem perovskite solar cells

Rational design and synthesis of high-performance doping-free hole transport polymers is critical to achieve high-efficiency and stable perovskite solar cells (PSCs). Side chain engineering is a widely employed strategy for modulating the photoelectronic properties of polymers. In this study, based on dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophenes (DTBDT) as D unit, benzo[d][1,2,3]triazole (BTA) as A segment, and thiophene as a π bridge, three D-π-A type polymeric materials with different length of alkyl side chain (PE51, PE52, and PE53) were utilized as hole transport materials in CsPbI2Br-based PSCs and perovskite/organic tandem solar cells (TSCs). With the increase of alkyl chain length from 2-butyloctyl (PE51) to 2-hexyldecyl (PE52) and to 2-octyldodecyl (PE53), the highest occupied molecular orbital energy level of the polymer gradually decreases, and the molecular stacking of the material gradually shifts from edge-on stacking to face-on stacking. Moreover, among three polymers, the PE53 exhibits the most efficient hole extraction at the CsPbI2Br/hole transport layer (HTL) interface. Hence, the CsPbI2Br-based PSCs and perovskite/organic TSCs employing PE53 as HTL realize the highest power conversion efficiency (PCE) of 17.65% and 23.07%, respectively. Our results indicate that side chain engineering of HTM is an effective strategy to modulate their molecular orientation and improve the photovoltaic performance of PSCs.

Theoretical Investigation of the Chemical Reactivity of Acrylic Acid Molecules: A DFT Study with UV-Vis, NMR, and FT-IR Spectroscopy Using STO-3G Basis Set

In this paper, quantum computational chemistry methods were employed to calculate the molecular characteristics of acrylic acid. Density Functional Theory (DFT) was used to optimize the molecule at the STO-3G basis set to calculate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the frontier orbitals of acrylic acid. The energy gap between HOMO-LUMO orbitals was calculated to be 5.545 eV. This demonstrated that the energy gap reflects the chemical activity of the molecule. The compound was characterized by UV-Visible, Nuclear Magnetic Resonance (NMR), and Fourier Transform Infrared (FT-IR) spectroscopy methods.

Molecular Engineering for Enhanced Thermoelectric Performance of Single-Walled Carbon Nanotubes/π-Conjugated Organic Small Molecule Hybrids.

Hybridizing single-walled carbon nanotubes (SWCNTs) with π-conjugated organic small molecules (π-OSMs) offers a promising approach for producing high-performance thermoelectric (TE) materials through the facile optimization of the molecular geometry and energy levels of π-OSMs. Designing a twisted molecular structure for the π-OSM with the highest occupied molecular orbital energy level comparable to the valence band of SWCNTs enables effective energy filtering between the two materials. The SWCNTs/twisted π-OSM hybrid exhibits a high Seebeck coefficient of 110.4 ± 2.6 µV K-1 , leading to a significantly improved power factor of 2,136 µW m-1 K-2 , which is 2.6 times higher than that of SWCNTs. Moreover, a maximum figure of merit over 0.13 at room temperature is achieved via the efficient TE transport of the SWCNTs/twisted π-OSM hybrid. The study highlights the promising potential of optimizing molecular engineering of π-OSMs for hybridization with SWCNTs to create next-generation, efficient TE materials.

3D hierarchical fireproof gel polymer electrolyte towards high-performance and comprehensive safety lithium-ion batteries

Gel polymer electrolyte (GPE) stands as an extensively investigated solid-state electrolytes for next-generation lithium-ion batteries (LIBs). Nonetheless, their inherent flammability necessitates the addition of flame retardants, which adversely impact LIBs’ electrochemical performance. Herein, we propose a groundbreaking conceive of a fireproof cross-linking composite GPE that united phosphene and a P-N synergistic flame retardant (DPM), equipping a dual-enhanced conduction effect on Li+ ions and a cooperative P-N flame-retardant effect. By strategically manipulating the polymer segments hierarchy and incorporating efficient function groups from DPM, freely Li+ mobility has been propelled, thereby delivering satisfactory ionic conductivity (1.263 mS cm−1, 20 ℃), elevated oxidative stability (5.42 V vs. Li+/Li) and improved Li+ transference number (0.53). The composite GPE-based batteries (LFP||Li, NCM523||Li and LFP||Graphite) indicate acceptable specific capacities at 1 C, together with good reversible capacity retention rate and stable coulombic efficiency after 200 cycles. Noticeably, the pouch cells (LFP||Graphite) assembled with composite GPE demonstrate superior safety robustness and fire-resistance under mechanical mishandling and ignition situations. Finally, the elucidation of Li+ ions interaction mechanism with polymer matrix is unraveled through molecular orbital energy levels and density function theory (DFT) calculation. This study offers valuable insights for harnessing novel electrolyte materials in high-safety LIBs.

Facile and green synthesis, crystal structure, antibacterial activity, Hirshfeld surface analysis, and computational investigation of a novel lithium(I) complex: Comparisons of theoretical and experimental analyses

A novel monovalent lithium complex, [Li(C6H4NO3)(H2O)2] (1), was prepared via a simple one-pot green reaction of 2-hydroxypyridine-3-carboxylic acid (2-hpca) with lithium carbonate and aminoguanidine (Amgu) bicarbonate in water. Complex 1 was investigated using elemental, ultraviolet–visible, Fourier transform infrared (FT-IR), thermal, and single-crystal X-ray diffraction (SC-XRD) measurements. We found that 1 crystallized in the monoclinic C2/m space group with a = 12.800(2) Å, b = 6.6657(13) Å, and c = 9.4687(19) Å. The Li ion exhibited four coordinates with a distorted square planar geometry. That is, the ion was surrounded by four oxygen atoms, of which two were derived from two water molecules, one was from the carboxylate group, and one was from the keto group of the 2-oxo-1,2-dihydropyridine-3-carboxylate ligand. Simultaneous thermogravimetry–differential thermal analysis of 1 exhibited dehydration followed by continuous low-temperature (∼400 °C) decomposition to produce lithium oxide as the end product in an air atmosphere. Furthermore, density functional theory (DFT) analysis was conducted to compare the theoretical and experimental data collected via SC-XRD. In addition, DFT was used to analyze the frontier molecular orbital energy levels and energy gaps. Moreover, we conducted Hirshfeld surface studies with respect to 1 to differentiate between the intermolecular hydrogen bond contacts. Energy frameworks for 1 were produced by analyzing the energy interactions between intermolecular hydrogen bonds to investigate the prevailing interactions involved in molecular packing. The in silico results showed that 1 has high potential for the development of antimicrobial drugs. Molecular docking studies were also conducted to determine the binding energy of 1 with Staphylococcus aureus (5CZZ) and Escherichia coli (3T88). The results were consistent with the experimental data obtained from the antibacterial activity of 1 with respect to Staphylococcus aureus and Escherichia coli.

Dual-functional chloropyrazine additives for enhanced performance of lithium-sulfur batteries

The commercialization of lithium-sulfur batteries (LSBs) faces challenges due to uncontrolled lithium deposition and lithium polysulfides (LiPSs) shuttling. In this study, a class of chloropyrazine-based electrolyte additives was introduced to address these issues. The results showed that the presence of chloropyrazine facilitated the formation of a robust and smooth organic-inorganic hybrid solid-electrolyte interface (SEI) enriched with LiCl. This SEI layer enabled reversible lithium plating/stripping, suppressed dendrite growth, and protected the lithium anode from detrimental side reactions with LiPSs. Furthermore, Density functional theory (DFT) results demonstrate that chloropyrazine additives effectively modulated the molecular orbital energy levels of LiPSs and promoted the kinetics of their conversion reactions. LSBs incorporating chloropyrazine additives demonstrated outstanding high-rate performance and long-term cycling stability, with over 800 cycles at 1 C rate and a capacity retention of 81.6 %. Even under challenging conditions of high sulfur loading (5.8 mg cm−2) and low electrolyte-to-sulfur ratio (5 μL mg−1), the battery demonstrated capacity decay rate of only 0.066 % per cycle after 500 cycles at 0.2 C rate. With the highlights of dual-functional chloropyrazine electrolyte additives in improving interfacial chemistry and modulating the orbital energy levels of LiPSs, this work offers a promising direction for advanced electrolyte design in LSBs.

Ambient-Stable n-Type Carbon Nanotube/Organic Small-Molecule Thermoelectrics Enabled by Energy Level Control.

The stability of n-type organic and hybrid thermoelectric materials is limited in terms of their practical application to p-n parallel thermoelectric devices. We demonstrate the ambient stability of an n-type single-walled carbon nanotube/organic small-molecule (SWNT/OSM) hybrid by deepening the lowest occupied molecular orbital energy level. This hybrid exhibited the best figure of merit (0.032) among n-type SWNT/OSM hybrid thermoelectrics and an enhanced power factor of 291.0 μW m-1 K-2. Furthermore, we observed that the n-type thermoelectric stability of a hybrid of SWNT and pip containing two N-ethylpiperidinyl groups on both sides of a naphthalenediimide core was retained at 87% over 7 months (220 days) under ambient conditions without encapsulation.

Ternary Organic Solar Cells by Small Amount of Efficient Light Absorption Polymer PSEHTT as Third Component Materials.

We prepared ternary organic solar cells (OSCs) by incorporating the medium wavelength absorption polymer PSEHTT into the PM6:L8-BO binary system. The power conversion efficiency (PCE) is improved from 15.83% to 16.66%. Although the fill factor (FF) is slightly reduced, the short-circuit current density (JSC) and open-circuit voltage (VOC) are significantly increased at the same time. A small amount of PSEHTT has a broad absorption spectrum in the short wavelength region and has good compatibility with PM6, which is conducive to fine-tuning the photon collection and improving the JSC. In addition, the highest occupied molecular orbital (HOMO) energy level of PSEHTT is deeper than that of PM6, which broadens the optical bandgap. This study provides an effective method to fabricate high-performance ternary OSCs by using a lower concentration of PSEHTT with PM6 as a hybrid donor material, which ensures a better surface and bulk morphology, improves photon collection, and broadens the optical bandgap.

Self-Reinforced Inductive Effect of Symmetric Bipolar Organic Molecule for High-Performance Rechargeable Batteries.

Herein, the self-reinforced inductive effect derived from coexistence of both p- and n-type redox-active motifs in a single organic molecule is presented. Molecular orbital energy levels of each motif are dramatically tuned, which leads to the higher oxidation and the lower reduction potentials. The self-reinforced inductive effect of the symmetric bipolar organic molecule, N,N'-dimethylquinacridone (DMQA), is corroborated, by both experimental and theoretical methods. Furthermore, its redox mechanism and reaction pathway in the Li+ -battery system are scrutinized. DMQA shows excellent capacity retention at the operating voltage of 3.85 and 2.09V (vs Li+ /Li) when used as the cathode and anode, respectively. Successful operation of DMQA electrodes in a symmetric all-organic battery is also demonstrated. The comprehensive insight into the energy storage capability of the symmetric bipolar organic molecule and its self-reinforced inductive effect is provided. Thus, a new class of organic electrode materials for symmetric all-organic batteries as well as conventional rechargeable batteries can be conceived.

Dynamic Variation of Rectification Observed in Supramolecular Mixed Mercaptoalkanoic Acid.

Functionality in molecular electronics relies on inclusion of molecular orbital energy level within a transmission window. This can be achieved by designing the active molecule with accessible energy levels or by widening the window. While many studies have adopted the first approach, the latter is challenging because defects in the active molecular component cause low breakdown voltages. Here, it is shown that control over the packing structure of monolayer via supramolecular mixing transforms an inert molecule into a highly tunable rectifier. Binary mixed monolayer composed of alkanethiolates with and without carboxylic acid head group as a proof of concept is formed via a surface-exchange reaction. The monolayer withstands high voltages up to |4.5 V| and shows a dynamic rectification-external bias relationship in magnitude and polarity. Sub-highest occupied molecular orbital (HOMO) levels activated by the widened transmission window account for these observations. This work demonstrates that simple supramolecular mixing can imbue new electrical properties in electro-inactive organic molecules.

Low-Temperature Cross-Linkable Hole Transport Materials for Solution-Processed Quantum Dot and Organic Light-Emitting Diodes with High Efficiency and Color Purity.

Cross-linkable hole transport materials (HTMs) are ideal for improving the performance of solution-processed quantum dot light-emitting diodes (QLEDs) and phosphorescent light-emitting diodes (OLEDs). However, previously developed cross-linkable HTMs possessed poor hole transport properties, high cross-linking temperatures, and long curing times. To achieve efficient cross-linkable HTMs with high mobility, low cross-linking temperature, and short curing time, we designed and synthesized a series of low-temperature cross-linkable HTMs comprising dibenzofuran (DBF) and 4-divinyltriphenylamine (TPA) segments for highly efficient solution-processed QLEDs and OLEDs. The introduction of divinyl-functionalized TPA in various positions of the DBF core remarkably affected their chemical, physical, and electrochemical properties. In particular, cross-linked 4-(dibenzo[b,d]furan-3-yl)-N,N-bis(4-vinylphenyl)aniline (3-CDTPA) exhibited a deep highest occupied molecular orbital energy level (5.50 eV), high hole mobility (2.44 × 10-4 cm2 V-1 s-1), low cross-linking temperature (150 °C), and short curing time (30 min). Furthermore, a green QLED with 3-CDTPA as the hole transport layer (HTL) exhibited a notable maximum external quantum efficiency (EQEmax) of 18.59% with a remarkable maximum current efficiency (CEmax) of 78.48 cd A-1. In addition, solution-processed green OLEDs with 3-CDTPA showed excellent device performance with an EQEmax of 15.61%, a CEmax of 52.51 cd A-1, and outstanding CIE(x, y) color coordinates of (0.29, 0.61). This is one of the highest reported EQEs and CEs with high color purity for green solution-processed QLEDs and OLEDs using a divinyl-functionalized cross-linked HTM as the HTL. We believe that this study provides a new strategy for designing and synthesizing practical cross-linakable HTMs with enhanced performance for highly efficient solution-processed QLEDs and OLEDs.

Novel bipolar host materials including carbazole and dioxy[2,3-b] pyrazine units for red phosphorescent organic light-emitting diodes

In this work, two novel bipolar host materials, 3,5-bis(9H-carbazol-9-yl) phenyl) benzo [1,4,5,6] dioxy [2,3-b] pyrazine (a-CzDp) and 7-(9-phenyl-9H-[3,9′- bicarbazole]-3′-yl) benzo [1,4,5,6] dioxy [2,3-b] pyrazine (b-CzDp) were designed and synthesized. In these two host materials, carbazole and dioxy [2,3-b] pyrazine act as the hole and electron transport unit, respectively. The two dipolar hosts both exhibit good thermal stability and deep highest occupied molecular orbital (HOMO) energy levels of -5.31 eV and −5.39 eV. The phosphorescent organic light-emitting diodes (PhOLEDs) including a-CzDp and b-CzDp as host and red phosphorescent material bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)2acac) as guest in the emitting layer. The corresponding PhOLED devices with a-CzDp and b-CzDp as host exhibit the maximum brightness of 8932 cd m−2 and 12782 cd m−2 at 624 nm, together with the maximum external quantum efficiency (EQE) of 10.32% and 13.82%, respectively. B-CzDp based red PhOLED device shows higher EQE and lower turn-on voltage due to the more balanced hole and electron transport. The results demonstrate the potential of a-CzDp and b-CzDp as efficient host for red PhOLEDs.