Умная лампа

Cationic palladium allyl complexes [η3-C3H5)Pd(k2P^O)]+SbF6- (2[SbF6],P^O= Ph2P(CH2)2C-(=O)OEt; 3[SbF6], o-Ph2PC6H4C(=O)OEt; 4[SbF6], Ph2P(CH2)2P(=O)Ph2) have been prepared. In all complexes the oxygen donor can be displaced by other ligands such as carbon monoxide and ethylene. Displacement of an ester donor occurs much more readily than displacement of the phosphine oxide function. Above 0°C, the resulting ethylene complexes [η3-C3H5)Pd(C2H4)(k1P~O)]+ react to give (1,2,5-η3)-pent-1-en-5-yl complexes [(H2C=CH(CH2)3Pd(k2P^O)]+. A rate constant of e.g. k(17°C) = (2.27 ± 0.11) × 10-4 s-1 was determined for P,O ≡ Ph2P(CH2)2C(O)OEt by 1H NMR spectroscopy. Using 2-4 as catalyst precursors for ethylene dimerization, the allyl moiety is ultimately cleaved from the metal center as 1,4-pentadiene

Electric-field fluctuations as the cause of spectral instabilities in colloidal quantum dots

Spectral diffusion (SD) represents a substantial obstacle towards implementation of solid-state quantum emitters as a source of indistinguishable photons. By performing high-resolution emission spectroscopy for individual colloidal quantum dots at cryogenic temperatures, we prove the causal link between the quantum-confined Stark effect and SD. Statistically analyzing the wavelength of emitted photons, we show that increasing the sensitivity of the transition energy to an applied electric field results in amplified spectral fluctuations. This relation is quantitatively fit to a straightforward model, indicating the presence of a stochastic electric field on a microscopic scale whose standard deviation is 9 kV/cm, on average. Compensating the commonly observed intrinsic electric bias with an external one, we find that SD can be suppressed by up to a factor of three in CdSe/CdS core/shell nanorods. The current method will enable the study of SD in multiple types of quantum emitters, such as solid-state defects or organic lead-halide perovskite quantum dots, for which spectral instability is a critical barrier for applications in quantum sensing

Mechanistic features of isomerizing alkoxycarbonylation of methyl oleate.

The weakly coordinated triflate complex [(P∧P)Pd(OTf)]+(OTf)− (1) (P∧ P = 1,3-bis(di-tert-butylphosphino) propane) is a suitable reactive precursor for mechanistic studies of the isomerizing alkoxcarbonylation of methyl oleate. Addition of CH3OH or CD3OD to 1 forms the hydride species [(P∧P)PdH(CH3OH)]+(OTf)− (2-CH3OH) or the deuteride [(P∧P)PdD(CD3OD)]+(OTf)− (2DCD3OD), respectively. Further reaction with pyridine cleanly affords the stable and isolable hydride [(P∧P)PdH- (pyridine)]+(OTf)− (2-pyr). This complex yields the hydride fragment free of methanol by abstraction of pyridine with BF3·OEt2, and thus provides an entry to mechanistic observations including intermediates reactive toward methanol. Exposure of methyl oleate (100 equiv) to 2D-CD3OD resulted in rapid isomerization to the thermodynamic isomer distribution, 94.3% of internal olefins, 5.5% of α,β-unsaturated ester and <0.2% of terminal olefin. Reaction of 2-pyr/BF3·OEt2 with a stoichiometric amount of 1-13C-labeled 1-octene at −80 °C yields a 50:50 mixture of the linear alkyls [(P∧P)Pd13CH2(CH2)6CH3]+ and [(P∧P)PdCH2(CH2)6 13CH3]+ (4a and 4b). Further reaction with 13CO yields the linear acyls [(P∧P)Pd13C(=O)12/13CH2(CH2)6 12/13CH3(L)]+ (5-L; L = solvent or 13CO). Reaction of 2-pyr/ BF3·OEt2 with a stoichiometric amount of methyl oleate at −80 °C also resulted in fast isomerization to form a linear alkyl species [(P∧P)PdCH2(CH2)16C(=O)OCH3]+ (6) and a branched alkyl stabilized by coordination of the ester carbonyl group as a four membered chelate [(P∧P)PdCH{(CH2)15CH3}C(=O)OCH3]+ (7). Addition of carbon monoxide (2.5 equiv) at −80 °C resulted in insertion to form the linear acyl carbonyl [(P∧P)PdC(=O)(CH2)17C(=O)OCH3(CO)]+ (8-CO) and the fivemembered chelate [(P∧P)PdC(=O)CH{(CH2)15CH3}C(=O)OCH3]+ (9). Exposure of 8-CO and 9 to 13CO at −50 °C results in gradual incorporation of the 13C label. Reversibility of 7 + CO ⇄ 9 is also evidenced by ΔG = −2.9 kcal mol−1 and ΔG‡ = 12.5 kcal mol−1 from DFT studies. Addition of methanol at −80 °C results in methanolysis of 8-L (L = solvent) to form the linear diester, 1,19-dimethylnonadecandioate, whereas 9 does not react and no branched diester is observed. DFT yields a barrier for methanolysis of ΔG‡ = 29.7 kcal mol−1 for the linear (8) vs ΔG‡ = 37.7 kcal mol−1 for the branched species (9)

Influence of Inner Shell Structure on the Encapsulation Behavior of Dexamethasone and Tacrolimus

We here present the synthesis and characterization of a set of biodegradable core–multishell (CMS) nanocarriers. The CMS nanocarrier structure consists of hyperbranched polyglycerol (hPG) as core material, a hydrophobic (12, 15, 18, 19, and 36 C-atoms) inner and a polyethylene glycol monomethyl ether (mPEG) outer shell that were conjugated by ester bonds only to reduce the toxicity of metabolites. The loading capacities (LC) of the drugs, dexamethasone and tacrolimus, and the aggregate formation, phase transitions, and degradation kinetics were determined. The intermediate inner shell length (C15) system had the best overall performance with good LCs for both drugs as well as a promising degradation and release kinetics, which are of interest for dermal deliver

Tailored Interface Energetics for Efficient Charge Separation in Metal Oxide-Polymer Solar Cells.

Hybrid organic-inorganic heterointerfaces in solar cells suffer from inefficient charge separation yet the origin of performance limitations are widely unknown. In this work, we focus on the role of metal oxide-polymer interface energetics in a charge generation process. For this purpose, we present novel benzothiadiazole based thiophene oligomers that tailor the surface energetics of the inorganic acceptor TiO2 systematically. In a simple bilayer structure with the donor polymer poly(3-hexylthiophene) (P3HT), we are able to improve the charge generation process considerably. By means of an electronic characterization of solar cell devices in combination with ultrafast broadband transient absorption spectroscopy, we demonstrate that this remarkable improvement in performance originates from reduced recombination of localized charge transfer states. In this context, fundamental design rules for interlayers are revealed, which assist the charge separation at organic-inorganic interfaces. Beside acting as a physical spacer in between electrons and holes, interlayers should offer (1) a large energy offset to drive exciton dissociation, (2) a push-pull building block to reduce the Coulomb binding energy of charge transfer states and (3) an energy cascade to limit carrier back diffusion towards the interface