Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: polymer hosts for high-efficiency light-emitting diodes

A carbazole homopolymer and carbazole copolymers based on 9,9'-dialkyl-[3,3']-bicarbazolyl, 2,5-diphenyl-[1,3,4]-oxadiazole and 9,9-bis(4-[3,7-dimethyloctyloxy]phenyl)fluorene were synthesized and their electrical and photophysical properties were characterized with respect to their application as host in phosphorescent polymer light-emitting diodes. It is shown that the triplet energy of a polymer depends on the specific connections between its building blocks. Without changing the composition of the polymer, its triplet energy can be increased from 2.3 to 2.6 eV by changing the way in which the different building blocks are coupled together. For poly(9-vinylcarbazole) (PVK), a carbazole polymer often used as host for high-energy triplet emitters in polymer light-emitting diodes, a large hole-injection barrier of about 1 eV exists due to the low-lying HOMO level of PVK. For all carbazole polymers presented here, the HOMO levels are much closer to the Fermi level of a commonly used anode such as ITO and/or a commonly used hole-injection layer such as PEDOT:PSS. This makes high current densities and consequently high luminance levels possible at moderate applied voltages in polymer light-emitting diodes. A double-layer polymer light-emitting diode is constructed comprising a PEDOT:PSS layer as hole-injection layer and a carbazole-oxadiazole copolymer doped with a green triplet emitter as emissive layer that shows an efficacy of 23 cd/A independent of current density and light output.     

Ethynylphosphonamidates for the Rapid and Cysteine‐Selective Generation of Efficacious Antibody–Drug Conjugates

Requirements for novel bioconjugation reactions for the synthesis of antibody–drug conjugates (ADCs) are exceptionally high, since conjugation selectivity as well as the stability and hydrophobicity of linkers and payloads drastically influence the performance and safety profile of the final product. We report Cys‐selective ethynylphosphonamidates as new reagents for the rapid generation of efficacious ADCs from native non‐engineered monoclonal antibodies through a simple one‐pot reduction and alkylation. Ethynylphosphonamidates can be easily substituted with hydrophilic residues, giving rise to electrophilic labeling reagents with tunable solubility properties. We demonstrate that ethynylphosphonamidate‐linked ADCs have excellent properties for next‐generation antibody therapeutics in terms of serum stability and in vivo antitumor activity.     

One-pot RAFT/"click" chemistry via isocyanates: efficient synthesis of α-end-functionalized polymers

A new methodology has been developed for preparing α-functional polymers in a one-pot simultaneous polymerization/isocyanate "click" reaction. Our original synthetic strategy is based on the preparation of a carbonyl-azide chain transfer agent (CTA) precursor that undergoes the Curtius rearrangement in situ during reversible addition-fragmentation chain transfer (RAFT) polymerization yielding well-controlled α-isocyanate modified polymers. This strategy overcomes numerous difficulties associated with the synthesis of a polymerization mediator bearing an isocyanate at the R group and with the handling of such a reactive functionality. This new carbonyl-azide CTA can control the polymerization of a wide range of monomers, including (meth)acrylates, acrylamides, and styrenes (M(n) = 2-30 kDa; ? = 1.16-1.38). We also show that this carbonyl-azide CTA can be used as a universal platform for the synthesis of α-end-functionalized polymers in a one-pot RAFT polymerization/isocyanate "click" procedure.     

Euphohelioscopin A Is a PKC Activator Capable of Inducing Macrophage Differentiation

To identify small molecules that selectively control hematopoietic stem cell differentiation, we performed an unbiased screen using primary human CD34(+) cells. We identified a plant-derived natural product, euphohelioscopin A, capable of selectively differentiating CD34(+) cells down the granulocyte/monocytic lineage. Euphohelioscopin A also inhibits proliferation and induces differentiation of the myeloid leukemia cell lines THP-1 and HL-60. Mechanistic studies revealed that euphohelioscopin A is an activator of protein kinase C (PKC), and that the promonocytic effects of this natural product are mediated by PKC activation. In addition to shedding insights into normal hematopoiesis, this work may ultimately facilitate the application of stem cell therapies to a host of myeloid dysfunctions.     

K3Cr2(PS4)3: A New Chromium Thiophosphate with a One‐Dimensional [Cr2(PS4)]3— Anion Chain

A new chromium thiophosphate, K₃Cr₂(PS₄)₃ has been prepared and characterized by single‐crystal diffraction, temperature dependent magnetic susceptibility measurements and optical spectroscopy. K₃Cr₂(PS₄)₃ crystallizes in the monoclinic space group P2₁/n (No. 14) with a = 9.731(2) Å, b = 11.986(2) Å, c = 17.727(4) Å, β = 96.52(2)°, V = 2054.2(2) ų, Z = 4, and R = 0.044. The anionic part of the structure consists of dimeric Cr₂(μ₃‐S₃PS)₂ units which are linked by bidentate PS₄ groups to form infinite one‐dimensional [S₂P_S2Cr₂(μ₃S₃P_S)₂]^3— chains separated by K⁺ cations. The Cr^III centers of the Cr₂(μ₃‐S₃PS)₂ units are antiferromagnetically coupled. The magnetic susceptibility data may be fitted using a D‐Heisenberg model for S = 3/2 with g = 2.02 and J/k = 10K. K₃Cr₂(PS₄)₃ is semiconducting with an optical band gap of 1.35 eV.     

Base‐Stabilized Boryl and Cationic Haloborylene Complexes of Iron

The synthesis of base‐stabilized boryl and borylene complexes is reported. An N‐heterocyclic carbene (NHC)‐stabilized iron–dihydroboryl complex was prepared by two different routes including methane liberation and salt elimination. A range of base‐stabilized iron–dichloroboryl complexes was prepared by addition of Lewis bases to boryl complexes. Base‐stabilized, cationic monochloroborylene complexes were synthesized from these boryl complexes by halide abstraction by using weakly coordinating anions.     

A highly porous flexible Metal-Organic Framework with corundum topology

A flexible Metal-Organic Framework Zn(4)O(BenzTB)(3/2) (DUT-13) was obtained by combination of a tetratopic linker and Zn(4)O(6+) as connector. The material has a corundum topology and shows the highest pore volume among flexible MOFs.     

Eu(3+)-mediated polymerization of benzenetetracarboxylic acid studied by spectroscopy, temperature-dependent calorimetry, and density functional theory

Thermodynamic parameters for the complexation of Eu(3+) with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerizable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 μM Eu(3+), <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60 °C. At elevated concentrations (>500 μM Eu(3+) and BTC) a temperature-dependent polymerization was observed, where BTC monomers are linked via coordinating shared Eu(3+) ions. The two methods lead to comparable thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol(-1); ΔS = 152 ± 5/130 ± 5 J mol(-1) K(-1); TRLFS/ITC) in the absence of polymerization. With the onset of polymerization, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly chelating coordination with two carboxylate groups in the monomeric complex and monodentate binding of a single carboxylate group in the polymeric complex of the polycarboxylate with Eu(3+). The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerization as a crucial factor in determining the effect of humic acids on the mobility of heavy metals in the environment.