Infrared Organic Light‐Emitting Diodes with Carbon Nanotube Emitters

While organic light‐emitting diodes (OLEDs) covering all colors of the visible spectrum are widespread, suitable organic emitter materials in the near‐infrared (nIR) beyond 800 nm are still lacking. Here, the first OLED based on single‐walled carbon nanotubes (SWCNTs) as the emitter is demonstrated. By using a multilayer stacked architecture with matching charge blocking and charge‐transport layers, narrow‐band electroluminescence at wavelengths between 1000 and 1200 nm is achieved, with spectral features characteristic of excitonic and trionic emission of the employed (6,5) SWCNTs. Here, the OLED performance is investigated in detail and it is found that local conduction hot‐spots lead to pronounced trion emission. Analysis of the emissive dipole orientation shows a strong horizontal alignment of the SWCNTs with an average inclination angle of 12.9° with respect to the plane, leading to an exceptionally high outcoupling efficiency of 49%. The SWCNT‐based OLEDs represent a highly attractive platform for emission across the entire nIR.     

Prüfung der mechanischen Eigenschaften von “Quenching und Partitioning”‐Gefügen mit berührungsloser Dehnungsmessung

The “Quenching and Partitioning” (“Q&P”) concept was designed to fill the gap between the first and second generation of Advanced High Strength Steels (AHSS). It aims at a multiphase microstructure of retained austenite in a matrix of carbon depleted martensite. The martensitic components enhance the strength properties. The ductility is improved by the TRIP effect. This work investigates the “quenching and partitioning” response of a nickel and silicium alloyed TRIP steel. After “quenching and partitioning” processing the mechanical properties are evaluated by tensile testing. An adapted specimen geometry and the contact free measurement of the elongation by a laser speckle system are used. The mechanical properties of the “quenching and partitioning” microstructure are compared to the fully martensitic state and reviewed with respect to published data. Additional tests are stopped after a well defined plastic deformation. Subsequently the retained austenite fraction is measured magnetically in the test length. As a result the TRIP effect can be evaluated. The “quenching and partitioning” processing leads to tensile strengths of around 1300 MPa at elongations of more than 10 %. The martensitic microstructure exhibits a higher tensile strength and lower elongation values. The decreasing fraction of retained austenite with plastic deformation implies the TRIP effect. Comparable mechanical properties are reported in the published literature. The proposed method of annealing and adapted testing shows effective for the investigation of sophisticated heat treatment procedures.     

Zero Linear Compressibility in Nondense Borates with a “Lu‐Ban Stool”‐Like Structure

Discovering materials that exhibit zero linear compressibility (ZLC) behavior under hydrostatic pressure is extremely difficult. To date, only a handful of ZLC materials have been found, and almost all of them are ultrahard materials with densified structures. Here, to explore ZLC in nondense materials, a structural model analogous to the structure of the “Lu‐Ban stool,” a product of traditional Chinese woodworking invented 2500 years ago, is proposed. The application of this model to borates leads to the discovery of ZLC in AEB₂O₄ (AE = Ca and Sr) with the unique “Lu‐Ban stool”‐like structure, which can obtain a subtle mechanical balance between pressure‐induced expansion and contraction effects. Coupled with the very wide ultraviolet transparent windows, the ZLC behavior of AEB₂O₄ may result in some unique but important applications. The applications of the “Lu‐Ban stool” model open a new route for pursuing ZLC materials in nondense structural systems.     

“One‐for‐All” Strategy in Fast Energy Storage: Production of Pillared MOF Nanorod‐Templated Positive/Negative Electrodes for the Application of High‐Performance Hybrid Supercapacitor

Currently, metal‐organic frameworks (MOFs) are intensively studied as active materials for electrochemical energy storage applications due to their tunable structure and exceptional porosities. Among them, water stable pillared MOFs with dual ligands have been reported to exhibit high supercapacitor (SC) performance. Herein, the “One‐for‐All” strategy is applied to synthesize both positive and negative electrodes of a hybrid SC (HSC) from a single pillared MOF. Specifically, Ni‐DMOF‐TM ([Ni(TMBDC)(DABCO)_0.5], TMBDC: 2,3,5,6‐tetramethyl‐1,4‐benzenedicarboxylic acid, DABCO: 1,4‐diazabicyclo[2.2.2]‐octane) nanorods are directly grown on carbon fiber paper (CFP) (denoted as CFP@TM‐nanorods) with the help of triethylamine and function as the positive electrode of HSC under alkaline electrolyte. Meanwhile, calcinated N‐doped hierarchical porous carbon nanorods (CFP@TM‐NPCs) are produced and utilized as the negative counter‐electrode from a one‐step heat treatment of CFP@TM‐nanorods. After assembling these two electrodes together to make a hybrid device, the TM‐nanorods//TM‐NPCs exhibit a wide voltage window of 1.5 V with a high sloping discharge plateau between 1‐1.2 V, indicating its great potential for practical applications. This as‐described “One‐for‐All” strategy is widely applicable and highly reproducible in producing MOF‐based electrode materials for HSC applications, which shortens the gap between experimental synthesis and practical application of MOFs in fast energy storage.     

Multiphotoluminescence from a Triphenylamine Derivative and Its Application in White Organic Light‐Emitting Diodes Based on a Single Emissive Layer

White organic light‐emitting diode (WOLED) technology has attracted considerable attention because of its potential use as a next‐generation solid‐state lighting source. However, most of the reported WOLEDs that employ the combination of multi‐emissive materials to generate white emission may suffer from color instability, high material cost, and a complex fabrication procedure which can be diminished by the single‐emitter‐based WOLED. Herein, a color‐tunable material, tris(4‐(phenylethynyl)phenyl)amine (TPEPA), is reported, whose photoluminescence (PL) spectrum is altered by adjusting the thermal annealing temperature nearly encompassing the entire visible spectra. Density functional theory calculations and transmission electron microscopy results offer mechanistic understanding of the PL redshift resulting from thermally activated rotation of benzene rings and rotation of 4‐(phenylethynyl) phenyl)amine connected to the central nitrogen atom that lead to formation of ordered molecular packing which improves the π–π stacking degree and increases electronic coupling. Further, by precisely controlling the annealing time and temperature, a white‐light OLED is fabricated with the maximum external quantum efficiency of 3.4% with TPEPA as the only emissive molecule. As far as it is known, thus far, this is the best performance achieved for single small organic molecule based WOLED devices.     

“Dual Lock‐and‐Key”‐Controlled Nanoprobes for Ultrahigh Specific Fluorescence Imaging in the Second Near‐Infrared Window

Fluorescence imaging in the second near‐infrared window (NIR‐II) is a new technique that permits visualization of deep anatomical features with unprecedented spatial resolution. Although attractive, effectively suppressing the interference signal of the background is still an enormous challenge for obtaining target‐specific NIR‐II imaging in the complex and dynamic physiological environment. Herein, dual‐pathological‐parameter cooperatively activatable NIR‐II fluorescence nanoprobes (HISSNPs) are developed whereby hyaluronic acid chains and disulfide bonds act as the “double locks” to lock the fluorescence‐quenched aggregation state of the NIR‐II fluorescence dyes for performing ultrahigh specific imaging of tumors in vivo. The fluorescence can be lit up only when the “double locks” are opened by reacting with the “dual smart keys” (overexpressed hyaluronidase and thiols in tumor) simultaneously. In vivo NIR‐II imaging shows that they reduce nonspecific activitation and achieve ultralow background fluorescence, which is 10.6‐fold lower than single‐parameter activatable probes (HINPs) in the liver at 15 h postinjection. Consequently, these “dual lock‐and‐key”‐controlled HISSNPs exhibit fivefold higher tumor‐to‐normal tissue ratio than “single lock‐and‐key”‐controlled HINPs at 24 h postinjection, attractively realizing ultrahigh specificity of tumor imaging. This is thought to be the first attempt at implementing ultralow background interference with the participation of multiple pathological parameters in NIR‐II fluorescence imaging.     

Defect/Edge‐Selective Functionalization of Carbon Materials by “Direct” Friedel–Crafts Acylation Reaction

Popularly utilized oxidation media, via nitric acid/sulfuric acid mixtures, are too corrosive and oxidizing to preserve structural integrity of highly ordered graphitic materials (carbon nanotubes (CNTs) and graphene). Here, for the most commonly used oxidation method, the important advantages of defect/edge‐selective functionalization of carbon materials (CNTs/graphene/graphite) in a polyphosphoric acid (PPA)/phosphorous pentoxide (P₂O₅) medium are elucidated. The optimized PPA/P₂O₅ medium is a mild acid that is not only less corrosive than popularly utilized oxidation media, but also has a strong capability to drive Friedel–Crafts acylation by covalently modifying carbon materials. With a broader spectrum of functional groups accessible, the PPA/P₂O₅‐driven Friedel–Crafts acylation offers more options for tailoring the properties and processing of carbon materials.