129 research outputs found
New Guanidine-Pyridine Copper Complexes and Their Application in ATRP
The guanidine hybrid ligands, (tetramethylguanidine)methylenepyridine (TMGpy) and (dimethylethyleneguanidine)methylenepyridine (DMEGpy), were proven to be able to stabilize copper complexes active in the solvent-free polymerization of styrene at 110 degrees C using 1-phenylethylbromide as the initiator. The polymerization proceeded after first-order kinetics, and polystyrenes with polydispersities around 1.2 could be obtained. Using the ligand, DMEGpy, three new copper guanidine-pyridine complexes could be synthesized and structurally characterized. Their structural characteristics are discussed
New Guanidine-Pyridine Copper Complexes and Their Application in ATRP
The guanidine hybrid ligands, (tetramethylguanidine)methylenepyridine (TMGpy) and (dimethylethyleneguanidine)methylenepyridine (DMEGpy), were proven to be able to stabilize copper complexes active in the solvent-free polymerization of styrene at 110 degrees C using 1-phenylethylbromide as the initiator. The polymerization proceeded after first-order kinetics, and polystyrenes with polydispersities around 1.2 could be obtained. Using the ligand, DMEGpy, three new copper guanidine-pyridine complexes could be synthesized and structurally characterized. Their structural characteristics are discussed
Cavity-enhanced single photon emission from a single impurity-bound exciton
Impurity-bound excitons in ZnSe quantum wells are bright single photon
emitters--a crucial element in photonics-based quantum technology. But to
achieve the efficiencies required for practical applications, these emitters
must be integrated into optical cavities that enhance their radiative
properties and far-field emission pattern. In this work, we demonstrate
cavity-enhanced emission from a single impurity-bound exciton in a ZnSe quantum
well. We utilize a bullseye cavity structure optimized to feature a small mode
volume and a nearly Gaussian far-field transverse mode that can efficiently
couple to an optical fiber. The fabricated device displays emission that is
more than an order of magnitude brighter than bulk impurity-bound exciton
emitters in the ZnSe quantum well, as-well-as clear anti-bunching, which
verifies the single photon emission from the source. Time-resolved
photoluminescence spectroscopy reveals a Purcell-enhanced radiative decay
process with a Purcell factor of 1.43. This work paves the way towards high
efficiency spin-photon interfaces using an impurity-doped II-VI semiconductor
coupled to nanophotonics
Extended spin coherence of the zinc-vacancy centers in ZnSe with fast optical access
Qubits based on crystal defect centers have been shown to exhibit long spin coherence times, up to seconds at room temperature. However, they are typically characterized by a comparatively slow initialization timescale. Here, fluorine implantation into ZnSe epilayers is used to induce defect states that are identified as zinc vacancies. We study the carrier spin relaxation in these samples using various pump-probe measurement methods, assessing phenomena such as resonant spin amplification, polarization recovery, and spin inertia in transverse or longitudinal magnetic field. The spin dynamics in isotopically natural ZnSe show a significant influence of the nuclear spin bath. Removing this source of relaxation by using isotopic purification, we isolate the anisotropic exchange interaction as the main spin dephasing mechanism and find spin coherence times of 100 ns at room temperature, with the possibility of fast optical access on the picosecond time scales through excitonic transitions of ZnSe
Tuning a robust system: N,O Zinc Guanidine Catalysts for the ROP of Lactide
Non-toxic, highly-active and robust complexes are the holy grail as ideal green catalysts for the polymerisation of biobased and biodegrable polylactide. Four new zinc guanidine complexes [ZnCl2(TMG4NMe2asme)], [ZnCl2(TMG5Clasme)], [ZnCl2(TMG5Measme)] and [ZnCl2(TMG5NMe2asme)] with different electron-donating and electron-withdrawing groups on aromatic backbone of the ligand have been synthesised. Ligands are derived from low-cost commercially available compounds and have been converted in a three- or four-step synthesis into the desired ligand in good yields. The compounds have been fully characterised and tested in the ROP of rac-LA in the melt under industrially relevant conditions. The complexes are based on the recently published structure [ZnCl2(TMGasme)] which has shown high activity in the polymerisation of lactide at 150 °C. Different substituents in the para-position to the guanidine moiety significantly increase the polymerisation rate whereas positioning substituents in meta-position causes no change in the reaction rate. With molecular weights over 71 000 g mol-1, the best catalyst produces polymer for several industrial applications and its polymerisation rate approaches the one of Sn(Oct)2. The robust systems are able to polymerise non-purified lactide. The initiation of the polymerisation is suggested to occur by impurities in the monomer
The MASi repository service : comprehensive, metadata-driven and multi-community research data management
Hiking on the potential energy surface of a functional tyrosinase model - implications of singlet, broken-symmetry and triplet description
The singlet, open-shell singlet and triplet potential energy surfaces (PES) for the peroxo state of a catalytic functional tyrosinase model have been investigated by density functional theory calculations. The broken-symmetry solution exhibits considerable stabilisation over the whole PES but the importance of the triplet state is unravelled as well
Introduction of selenide based nanostructures: Recent applications and potential in quantum optics
- …