Single-emissive-layer all-perovskite white light-emitting diodes employing segregated mixed halide perovskite crystals

Metal halide perovskites have demonstrated impressive properties for achieving efficient monochromatic light-emitting diodes. However, the development of white perovskite light-emitting diodes (PeLEDs) remains a big challenge. Here, we demonstrate a single-emissive-layer all-perovskite white PeLED using a mixed halide perovskite film as the emissive layer. The perovskite film consists of separated mixed halide perovskite phases with blue and red emissions, which are beneficial for suppressing halide anion exchange and preventing charge transfer. As a result, the white PeLED shows balanced white light emission with Commission Internationale de L''Eclairage coordinates of (0.33, 0.33). In addition, we find that the achievement of white light emission from mixed halide perovskites strongly depends on effective modulation of the halide salt precursors, especially lead bromide and benzamidine hydrochloride in our case. Our work provides very useful guidelines for realizing single-emissive-layer all-perovskite white PeLEDs based on mixed halide perovskites, which will spur the development of high-performance white PeLEDs.

We demonstrated a single-emissive-layer all-perovskite white light-emitting diode based on a mixed halide perovskite film.     

Purcell Effect and Nonlinear Behavior of the Emission in a Periodic Structure Composed of InAs Monolayers Embedded in a GaAs Matrix

Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time‐resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super‐radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near‐quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non‐monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures.     

Continuous reaction system to investigate the dispersion polymerization of vinyl monomers in supercritical carbon dioxide

A laboratory‐scale continuous reaction system using a stirred tank reactor was assembled in our laboratory to study the dispersion polymerization of vinyl monomers in supercritical carbon dioxide (scCO₂). The apparatus was equipped with a suitable downstream separation section to collect solid particles entrained in the effluent stream from the reactor, whose monomer concentration could be measured online with a gas chromatograph. The dispersion polymerization of methyl methacrylate in scCO₂ was selected as a model process to be investigated in the apparatus. The experiments were performed at 65 °C and 25 MPa with 2,2′‐azobisisobutyronitrile as the initiator and a reactive polysiloxane macromonomer as a surfactant to investigate the effect of the mean residence time of the reaction mixture on the monomer conversion, polymerization rate, polymer molecular weight, and particle size distribution. The results were compared with those obtained in batch polymerizations carried out under similar operative conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4122–4135, 2006     

Direct aerobic epoxidation of alkenes catalyzed by metal nanoparticles stabilized by the H5PV2Mo10O40 polyoxometalate

Ag and Ru nanoparticles stabilized by H5PV2Mo10O40, prepared by a sequence of redox reactions and supported on alpha-alumina, were effective catalysts for the direct aerobic epoxidation of alkenes in the liquid phase.     

Selective mono-N-alkylation of 3-amino alcohols via chelation to 9-BBN

[reaction: see text] A method for selective mono-N-alkylation of amino alcohols is introduced. This method relies on formation of a stable chelate with 9-BBN, which serves in the dual roles of protecting and activating the amine group. Three prototypical amino alcohols featuring various three-carbon bridging units led selectively to the monoalkylated derivatives in very high yields. The straightforward synthesis of the N-CD3 derivatives demonstrates the effectiveness of this approach.     

Sequence and Structure of Peptoid Oligomers Can Tune the Photoluminescence of an Embedded Ruthenium Dye

The understanding of structure–function relationships within synthetic biomimetic systems is a fundamental challenge in chemistry. Herein we report the direct correlation between the structure of short peptoid ligands—N-substituted glycine oligomers incorporating 2,2′-bipyridine groups—varied in their monomer sequence, and the photoluminescence of Ru^II centers coordinated by these ligands. Based on circular dichroism and fluorescence spectroscopy we demonstrate that while helical peptoids do not affect the fluorescence of the embedded Ru^II chromophore, unstructured peptoids lead to its significant decay. Transmittance electron microscopy (TEM) revealed significant differences in the arrangements of metal-bound helical versus unstructured peptoids, suggesting that only the latter can have through-space interactions with the ruthenium dye leading to its quenching. High-resolution TEM enabled the remarkable direct imaging of singular ruthenium-bound peptoids and bundles, supporting our explanation for structure-depended quenching. Moreover, this correlation allowed us to fine-tune the luminescence properties of the complexes simply by modifying the sequence of their peptoid ligands. Finally, we also describe the chiral properties of these Ru–peptoids and demonstrate that remote chiral induction from the peptoids backbone to the ruthenium center is only possible when the peptoids are both chiral and helical.     

Palladium nanoparticles stabilized by alkylated polyethyleneimine as aqueous biphasic catalysts for the chemoselective stereocontrolled hydrogenation of alkenes

Palladium nanoparticles were prepared, stabilized, and dispersed in water by alkylated branched polyethyleneimine. The palladium nanoparticles were effective aqueous biphasic catalysts for the chemoselective hydrogenation of alkenes with preferential reduction of less hindered double bonds, such as reduction of 3-methylcyclohexene in the presence of 1-methylcyclohexene and 1-octene in the presence of 2-methyl-2-heptene. [structure: see text].     

Detection and Characterization of Boric Acid and Borate Ion Binding to Cytochrome c Using Multiple Quantum Filtered NMR

The application of multiple quantum filtered (MQF) NMR to the identification and characterization of the binding of ligands containing quadrupolar nuclei to proteins is demonstrated. Using relaxation times measured by MQF NMR multiple binding of boric acid and borate ion to ferri and ferrocytochrome c was detected. Borate ion was found to have two different binding sites. One of them was in slow exchange, k_diss = 20 ± 3 s⁻¹ at 5°C and D₂O solution, in agreement with previous findings by ¹H NMR (G. Taler et al., 1998, Inorg. Chim. Acta 273, 388–392). The triple quantum relaxation of the borate in this site was found to be governed by dipolar interaction corresponding to an average B–H distance of 2.06 ± 0.07 Å. Other, fast exchanging sites for borate and boric acid could be detected only by MQF NMR. The binding equilibrium constants at these sites at pH 9.7 were found to be 1800 ± 200 M⁻¹ and 2.6 ± 1.5 M⁻¹ for the borate ion and boric acid, respectively. Thus, detection of binding by MQF NMR proved to be sensitive to fast exchanging ligands as well as to very weak binding that could not be detected using conventional methods.     

Copolymerization of VDF and HFP in Supercritical Carbon Dioxide: A Robust Approach for Modeling Precipitation and Dispersion Kinetics

A kinetic model is developed for the heterogeneous free‐radical copolymerization of vinylidene fluoride and hexafluoropropylene in supercritical CO₂. The model accounts for polymerization in both the dispersed (polymer‐rich) phase and in the continuous (polymer‐free) supercritical phase, for radical interphase transport, diffusion limitations, and chain‐length‐dependent termination in the polymer‐rich phase. A parameter evaluation strategy is developed and detailed to estimate most of the kinetic parameters a priori while minimizing their evaluation by direct fitting. The resulting model predictions compare favorably with the experimental results of conversion and MWD at varying monomer feed composition, monomer concentration, interphase area, and pressure of the system.