Multiple exciton generation in nano-crystals revisited: Consistent calculation of the yield based on pump-probe spectroscopy

Multiple exciton generation (MEG) is a process in which more than one exciton is generated upon the absorption of a high energy photon, typically higher than two times the band gap, in semiconductor nanocrystals. It can be observed experimentally using time resolved spectroscopy such as the transient absorption measurements. Quantification of the MEG yield is usu- ally done by assuming that the bi-exciton signal is twice the signal from a single exciton. Herein we show that this assumption is not always justified and may lead to significant errors in the estimated MEG yields. We develop a methodology to determine proper scaling factors to the signals from the transient absorption experiments. Using the methodology we find modest MEG yields in lead chalcogenide nanocrystals including the nanorods

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Unsymmetric PCN Pincer Palladium and Nickel Complexes : Synthesis, Characterization and Reactivity

New palladium and nickel complexes based on unsymmetric PCN pincer ligands have been synthesized and fully characterized using different techniques. The substituents on the nitrogen side arm of the ligand have great influence on the cyclometallation and the reactivity of the new complexes particularly in case of nickel. The less sterically hindered PCNMe ligand enabled formation of the trivalent nickel halide complexes through a straightforward reaction with anhydrous copper halide salts. The trivalent nickel halide complexes were isolated and characterized using EPR, magnetic moment and elemental analysis. The reactivity of the PCN nickel halide complexes in Kharasch addition was tested.The PCN palladium and nickel complexes relevant to CO2 insertion reactions were synthesized, and their reactivity towards CO2 were investigated giving facile insertion reactions at room temperature in case of the hydroxo and amido complexes. Insertion of CO2 into the nickel methyl bond was conducted under mild reaction conditions using the more electron donating and the sterically hindered PCNi-Pr ligand. Insertion of CO2 into the palladium phenyl acetylide complex offered the corresponding hydrogen carbonate complex. Investigation of the identity of the later complex led to the development of catalytic decarboxylative cross coupling reaction.A short synthetic route was developed to prepare the PCNPy nickel complexes including pyridine as a nitrogen side arm. The new PCNPy allowed C-H activation at room temperature and enhanced the stability of the alkyl nickel complexes. The PCN nickel complexes mediate the catalytic Kumada coupling reaction

Synthesis and Reactivity of (PCNMe) Pincer Palladium Complexes

New (PCNMe) pincer Pd(II) complexes were synthesized and their properties were studied in various reactions. (PCNMe)Pd-Br was synthesized and employed as catalyst for Suzuki cross-coupling reactions of aryl halides (e.g. bromobenzene, 4-bromotoulene and 4-bromobenzaldehyde) with phenylboronic acids (e.g. phenylboronic acid, 4-formyl phenylboronic acid and p-tolyl boronic acid). High yields and high turnover numbers were achieved using catalyst loading of only 0.05 %. To gain deeper insight into the mechanism of this coupling reactions (PCNMe)Pd complexes bearing palladium carbon bonds were synthesized and its reactivity with aryl halides (or phenyl bromide) was studied. In kinetic experiments the influence of different additives on the reaction were analyzed to investigate their role in the C-C coupling step.Popular Science Summary Synthesis and Reactivity of (PCNMe) Pincer Pd(II) Complexes Cross coupling reactions are considered one of the most important in the field of organic chemistry where C-C and C-X (X= Heteroatom) bonds easy to form in presence of catalyst. These reactions have been employed to synthesize different types of drugs, polymers and agricultural chemicals. Palladium complexes were employed as catalysts for these reactions especially the complexes which are produced from the cyclometallation of tridentate ligand known as pincer ligand with palladium. Pincer palladium complexes are thermally stable and are not sensitive to air and moisture so it’s easy to be handled in contrast to the traditional Pd(0) complexes. The aim of this work is to study the mechanism of C-C bond formation. Therefore, (PCNMe)Pd-Phenylacetylide was synthesized and was reacted with bromobenzene in presence and absence of additives. Nuclear Magnetic Resonance (NMR) was very useful tool during this study where 1 H- and 31P-NMR spectra were measured during the course of the reaction. By interpreting the spectra and by studying the influence of different additives in the progress of the reaction, a mechanism involving soluble Pd(0) would be suggested for the formation of the cross coupling product

Synthesis and Characterization of PbS Quantum Dots

Colloidal semiconductor nanocrystals or quantum dots (QDs) have recently attracted much attention because of their unique electronic and optical properties and potential for a wide range of applications. Near-infrared (NIR) PbS QDs were synthesized using oleic acid (OA) as a surfactant for stabilizing the nanocrystals. PbS QD’s of different diameters were obtained by varying the injection temperature from 90-120 oC. The absorption and fluorescence measurements were recorded and the fluorescence quantum yield relative to IR-125 dye has been measured

Synthesis, Characterization, and Reactivity of PCN Pincer Nickel Complexes

New diamagnetic nickel(II) complexes based on an unsymmetrical (1-(3-((ditert-butylphosphino)methyl)phenyl)-N,N-dimethyl-methanamine) (PCN) pincer ligand were synthesized and characterized by 1H, 31P{1H}, and 13C{1H} NMR spectroscopy. Their molecular structures were confirmed by X-ray diffraction. Oxidation to high-valent paramagnetic Ni(III) dihalide complexes was achieved through straightforward reaction of the corresponding diamagnetic halide complexes with anhydrous CuX2 (X = Cl, Br). In agreement with this, the complexes are active in Kharasch addition of CCl4 to olefins. The reaction of the hydroxo complex (8) and the amido complex (11) with CO2 produced the hydrogen carbonate and carbamate complexes, respectively. The hydrogen carbonate complex was converted to the dinuclear nickel carbonate complex (10). The methyl (13), phenyl (14), and p-tolylacetylide (15) complexes are also described in the current study providing the first example of the hydrocarbyl nickel complexes based on an unsymmetric aromatic pincer ligand. Furthermore, the reactivity of the methyl complex toward different electrophiles has been investigated, showing that C-C bond formation is possible with aryl halides, whereas the reaction with CO2 is sluggish

Synthesis and characterisation of POCsp3OP supported Ni(II) hydroxo, hydroxycarbonyl and carbonate complexes

A nickel(II) hydroxo complex (3) supported by a cyclohexyl based POCsp3OP pincer ligand (POCsp3OP = cis-1,3-Bis-(di-tert-butylphosphinito)cyclohexyl) is reported. Complex 3 reacts with CO to form the corresponding hydroxycarbonyl complex, (POCsp3OP)NiCOOH (4). Complex 3 is also reactive towards CO2, forming a bicarbonate species (5) that under reduced pressure loses 1/2 eq. of H2O and CO2 to give a binuclear, bridged carbonate complex (6). All compounds were characterized in the solid state by X-ray diffraction

Aromatic PCN pincer palladium complexes : Forming and breaking CC bonds

Through a salt metathesis reaction, ( t-BuPCN)Pd-ONO2 (2) was prepared and used as a precursor for producing ( t-BuPCN)Pd-OH (3) and ( t-BuPCN)Pd-aryl acetylide complexes 4 (phenyl acetylide) and 5 (p-tolyl acetylide). The aryl acetylide complexes could also be prepared through another synthetic route: by condensation of 3 with the corresponding aryl acetylene. The reactivity of complexes 3 and 4 toward carbon dioxide was studied and it was found that both reactions give the hydrogen carbonate complex (6). The low reactivity of the Pd-acetylide bond was further confirmed by the fact that the propiolate complex undergoes decarboxylation to give 4. PCN palladium complexes are good catalysts for the decarboxylative cross coupling reactions between acetylene carboxylic acids and aryl halides. The yield of the cross coupling product was improved by adding a catalytic amount of CuI

Synthesis, Characterization, and Reactivity of PCN Pincer Nickel Complexes

New diamagnetic nickel­(II) complexes based on an unsymmetrical (1-(3-((di<i>tert</i>-butylphosphino)­methyl)­phenyl)-<i>N</i>,<i>N</i>-dimethyl-methanamine) (PCN) pincer ligand were synthesized and characterized by ¹H, ³¹P­{¹H}, and ¹³C­{¹H} NMR spectroscopy. Their molecular structures were confirmed by X-ray diffraction. Oxidation to high-valent paramagnetic Ni­(III) dihalide complexes was achieved through straightforward reaction of the corresponding diamagnetic halide complexes with anhydrous CuX₂ (X = Cl, Br). In agreement with this, the complexes are active in Kharasch addition of CCl₄ to olefins. The reaction of the hydroxo complex (<b>8</b>) and the amido complex (<b>11</b>) with CO₂ produced the hydrogen carbonate and carbamate complexes, respectively. The hydrogen carbonate complex was converted to the dinuclear nickel carbonate complex (<b>10</b>). The methyl (<b>13</b>), phenyl (<b>14</b>), and <i>p</i>-tolylacetylide (<b>15</b>) complexes are also described in the current study providing the first example of the hydrocarbyl nickel complexes based on an unsymmetric aromatic pincer ligand. Furthermore, the reactivity of the methyl complex toward different electrophiles has been investigated, showing that C–C bond formation is possible with aryl halides, whereas the reaction with CO₂ is sluggish

Carboxylation of the Ni-Me Bond in an Electron-Rich Unsymmetrical PCN Pincer Nickel Complex

The synthesis of a new unsymmetrical PCN ligand bearing tert-butyl groups on the phosphorus atom and isopropyl groups on the nitrogen donor atom is presented. It reacts with the commercially available Ni(DME)Br2 precursor to offer the corresponding t-BuPCNi-Pr pincer nickel bromide complex 1 together with a paramagnetic species, which was characterized as a tetrahedral nickel complex. Complex 1 reacts with MeMgCl to give the corresponding methyl complex 3. Carboxylation of complex 3 using 4 atm of CO2 gave the PCN nickel acetate complex 4 under mild reaction conditions comparable to those for the corresponding palladium complexes with PCP ligands