Improved stability of molecular organic EL devices

Influence of emission sites on emission efficiency and running durability of molecular organic electroluminescent devices was investigated. When fluorescent dye rubrene was doped into TPD diamine hole transport layer, rubrene molecule emitted bright yellow light with a max. luminance of 61 000 cd/m². The device had the highest efficiency of 9.8 Im/W at 100 cd/m². Half-decay time of the device from initial luminance of 530 cd/m² under constant direct current was 3 600 h. On the other hand, when rubrene was doped into BeBq₂ complex electron transport layer, the efficiency was 4.4 Im/W and the half-decay time was 110 h. Thus doping site is found to exert significant influence both on the emission efficiency and the running durability.     

Structural analysis of certain linear operators representing chemical network systems via the existence and uniqueness theorems of spectral resolution. IV

Part IV of this series consists of two complementary subparts devoted to attain the following two goals: (i) By shifting from the previous setting of the Banach algebra B (ℬ︁)= B (ℬ︁, ℬ︁) to a broader setting of the space B (X, ℬ︁) of all bounded linear operators from a normed space X to a Banach space ℬ︁, we extend our previous theoretical framework to incorporate part of the theory of additive correlation involving the Asymptotic Linearity Theorems, which have been developed for a study of correlation between structure and properties in molecules having many identical moieties, especially in macromolecules having repeating units. (ii) By reverting our focus to the special algebra B (ℋ︁) with ℋ︁ being a Hilbert space, we develop a theorem which is useful for a structural analysis of spectral symmetry of linear operators representing physico-chemical network systems. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67 : 57–69, 1998     

Carbazole-2-carbonitrile as an acceptor in deep-blue thermally activated delayed fluorescence emitters for narrowing charge-transfer emissions

This work reports a new acceptor for constructing donor–acceptor type (D–A type) blue thermally activated delayed fluorescence (TADF) emitters with narrowed charge-transfer (CT) emissions. A new acceptor core, carbazole-2-carbonitrile (CCN), is formed by the fusion of carbazole and benzonitrile. Three D–A type TADF emitters based on the CCN acceptor, namely 3CzCCN, 3MeCzCCN, and 3PhCzCCN, have been successfully synthesized and characterized. These emitters show deep-blue emissions from 439 to 457 nm with high photoluminescence quantum yields of up to 85% in degassed toluene solutions. Interestingly, all CCN-based deep-blue TADF emitters result in narrow CT emissions with full-width at half-maximums (FWHMs) of less than 50 nm in toluene solutions, which are pretty narrower compared with those of typical D–A type TADF emitters. Devices based on these emitters show high maximum external quantum efficiencies of up to 17.5%.

Deep-blue donor–acceptor thermally activated delayed fluorescence emitters based on carbazole-2-carbonitrile are synthesized, resulting in narrow emission with full-width at half-maximums of less than 50 nm and a maximum OLED EQE of up to 17.5%.     

Fabrication of Micro-Optic Elements by the Sol-Gel Method

Micro-lens arrays composed of organic-inorganic materials were molded on glass substrates by the sol-gel method. Each lens had the same focal length and accurate pitch. There was no change in appearance or focal length after heat treatment at 350°C. The arrays had a refractive index of 1.53 (@1550 nm) and a transmittance of 98%/mm (@1550 nm). The film material did not change in appearance during evaluation for acid resistance.     

Tetrahydroimidazo[1,2-a]pyrazine Derivatives: Synthesis and Evaluation as Gαq-Protein Ligands

The 5,6,7,8-tetrahydroimidazo[1,2-a]pyrazine derivative BIM-46174 and its dimeric form BIM-46187 ( 1 ) are heterocyclized dipeptides that belong to the very few cell-permeable compounds known to preferentially silence Gα_q proteins. To explore the chemical space of Gα_q inhibitors of the BIM chemotype, a combinatorial approach was conducted towards a library of BIM molecules. This library was evaluated in a second messenger-based fluorescence assay to analyze the activity of Gα_q proteins through the determination of intracellular myo-inositol 1-phosphate. Structure–activity relationships were deduced and structural requirements for biological activity obtained, which were (i) a redox reactive thiol/disulfane substructure, (ii) an N-terminal basic amino group, (iii) a cyclohexylalanine moiety, and (iv) a bicyclic skeleton. Active compounds exhibited cellular toxicity, which was investigated in detail for the prototypical inhibitor 1 . This compound affects the structural cytoskeletal dynamics in a Gα_q/11-independent manner.     

Biodegradable and Electroactive TEMPO‐Substituted Acrylamide/Lactide Copolymers

Copolymers composed of PLA and PTAm were prepared by a macromonomer approach. The PLA bearing vinyl group at chain end was copolymerized with 2,2,6,6‐tetrametylpiperidine‐4‐ylacrylamide. The resulted copolymers were oxidized by a peroxide to give PTAm‐g‐PLA. The structures of the copolymers were confirmed by NMR and FTIR spectroscopy. The comparison of ¹H NMR results and SQUID measurements demonstrated that the oxidation of the PTAm fragment proceeded almost to completion. An MTT assay, cell adhesion and spreading evaluation showed that the copolymers exhibited improved cytocompatibility as compared to the PTAm homopolymer due to the introduction of the biocompatible PLA moiety.

     

Dynamic structural changes at LiMn2O4/electrolyte interface during lithium battery reaction

Gaining a thorough understanding of the reactions on the electrode surfaces of lithium batteries is critical for designing new electrode materials suitable for high-power, long-life operation. A technique for directly observing surface structural changes has been developed that employs an epitaxial LiMn(2)O(4) thin-film model electrode and surface X-ray diffraction (SXRD). Epitaxial LiMn(2)O(4) thin films with restricted lattice planes (111) and (110) are grown on SrTiO(3) substrates by pulsed laser deposition. In situ SXRD studies have revealed dynamic structural changes that reduce the atomic symmetry at the electrode surface during the initial electrochemical reaction. The surface structural changes commence with the formation of an electric double layer, which is followed by surface reconstruction when a voltage is applied in the first charge process. Transmission electron microscopy images after 10 cycles confirm the formation of a solid electrolyte interface (SEI) layer on both the (111) and (110) surfaces and Mn dissolution from the (110) surface. The (111) surface is more stable than the (110) surface. The electrode stability of LiMn(2)O(4) depends on the reaction rate of SEI formation and the stability of the reconstructed surface structure.     

The Role of Hydrophobicity in the Antimicrobial and Hemolytic Activities of Polymethacrylate Derivatives

We synthesized cationic random amphiphilic copolymers by radical copolymerization of methacrylate monomers with cationic or hydrophobic groups and evaluated their antimicrobial and hemolytic activities. The nature of the hydrophobic groups, and polymer composition and length were systematically varied to investigate how structural parameters affect polymer activity. This allowed us to obtain the optimal composition of polymers suitable to act as non-toxic antimicrobials as well as non-selective polymeric biocides. The antimicrobial activity depends sigmoidally on the mole fraction of hydrophobic groups (f_HB). The hemolytic activity increases as f_HB increases and levels off at high values of f_HB, especially for the high-molecular-weight polymers. Plots of HC₅₀ values versus the number of hydrophobic side chains in a polymer chain for each polymer series showed a good correlation and linear relationship in the log–log plots. We also developed a theoretical model to analyze the hemolytic activity of polymers and demonstrated that the hemolytic activity can be described as a balance of membrane binding of polymers through partitioning of hydrophobic side chains into lipid layers and the hydrophobic collapsing of polymer chains. The study on the membrane binding of dye-labeled polymers to large, unilamellar vesicles showed that the hydrophobicity of polymers enhances their binding to lipid bilayers and induces collapse of the polymer chain in solution, reducing the apparent affinity of polymers for the membranes.     

Jewelry Box of Morphologies with Mesoscopic Length Scales – ABC Star‐shaped Terpolymers

Among several star molecules studied so far, the results for two similar but slightly different systems composed of all hydrophobic components, i.e. one low T_g arm and two high T_g arms were compared and discussed mainly. They are polyisoprene‐arm‐polystyrene‐arm‐poly(2‐vinylpyridine) stars and polystyrene‐arm‐polybutadiene‐arm‐poly(2‐vinylpyridine) ones, and are abbreviated as ISP and SBV, respectively, in the original literatures. Several periodic Archimedean tiling patterns can be naturally formed when the relative lengths of three chains are similar one another in both series. Core‐shell type morphologies and actually three‐phase four layer lamellar structures were also commonly observed for two series. A quasicrystalline tiling with dodecagonal symmetry can also be conformed at the targeted composition of ISP/homopolymer blend and a zinc‐blende type structure was created at just a little outside of tiling region for the same blend. Furthermore, the several interesting structures from amphiphilic molecules, composed of a hydrophilic component, poly(ethylene oxide), a hydrophobic component, polymethylmethacrylate and a highly water‐repellent polymer poly(perfluoropropyleneoxide) are described and introduced.