Efficient exfoliation of UV-curable, high-quality graphene from graphite in common low-boiling-point organic solvents with a designer hyperbranched polyethylene copolymer and their applications in electrothermal heaters.

The use of stabilizer with designer structures can effectively promote graphite exfoliation in common solvents to render functionalized graphene desirable for their various applications. Herein, a hyperbranched polyethylene copolymer, HBPE@Py@Acryl, simultaneously bearing multiple pyrene terminal groups and pendant acryloyl moieties has been successfully synthesized from ethylene with a Pd-diimine catalyst based on unique chain walking mechanism. The unique structural design of the HBPE@Py@Acryl makes it capable of effectively promote graphite exfoliation in a series of common, low-boiling-point organic solvents, e.g. CHCl3, to render stable graphene dispersions with concentrations effectively adjustable by changing feed concentrations of graphite and polymer or sonication time. Meanwhile, it can be irreversibly adsorbed on the exfoliated graphene surface based on the π-π interactions between them to concurrently render acryloyl-functionalized graphene free of structural defects, with majority (92.7%) of them having a thickness of 2-3 layers. This allows us to obtain graphene electrothermal films simply by filtration and UV irradiation, which exhibit outstanding stability in use. The action mechanism of the HBPE@Py@Acryl as stabilizer for promoting graphite exfoliation and the role of UV irradiation on improving the stability in use of resulting graphene films have been elucidated.

Theoretical study of the mechanical properties of CrFeCoNiMo x (0.1 ≤ x ≤ 0.3) alloys.

Based on exact muffin-tin orbitals (EMTO) and coherent potential approximation (CPA), we investigate the effects of Mo content on the mechanical properties of CrFeCoNiMo x (0.1 ≤ x ≤ 0.3) high-entropy alloys (HEAs) with a face-centered-cubic (fcc) crystal structure; relevant physical parameters are calculated as a function of Mo content. The results indicate that the theoretical predictions of lattice constant, elastic constants, shear modulus, and Young's modulus are in good agreement with the available experimental data, which proves the validity of the applied approach. CrFeCoNiMo0.26 HEA has better ductility and plasticity with respect to other HEAs with different Mo contents because it has the minimum elastic moduli and Vickers hardness, and has the maximum Pugh's ratio and anisotropy factors, etc. CrFeCoNiMo0.2 HEA has better plasticity compared with CrFeCoNiMo0.1 and CrFeCoNiMo0.3 HEAs due to its minimum energy factor and maximum dislocation width. Screw dislocation is more likely to nucleate in CrFeCoNiMo x (0.1 ≤ x ≤ 0.3) HEAs than edge dislocation. The present studies are helpful to explore the excellent mechanical properties of CrFeCoNiMo x (0.1 ≤ x ≤ 0.3) HEAs during experiments.

Light-induced picosecond rotational disordering of the inorganic sublattice in hybrid perovskites.

Femtosecond resolution electron scattering techniques are applied to resolve the first atomic-scale steps following absorption of a photon in the prototypical hybrid perovskite methylammonium lead iodide. Following above-gap photoexcitation, we directly resolve the transfer of energy from hot carriers to the lattice by recording changes in the mean square atomic displacements on 10-ps time scales. Measurements of the time-dependent pair distribution function show an unexpected broadening of the iodine-iodine correlation function while preserving the Pb-I distance. This indicates the formation of a rotationally disordered halide octahedral structure developing on picosecond time scales. This work shows the important role of light-induced structural deformations within the inorganic sublattice in elucidating the unique optoelectronic functionality exhibited by hybrid perovskites and provides new understanding of hot carrier-lattice interactions, which fundamentally determine solar cell efficiencies.

Exploring Flow Procedures for Diazonium Formation.

The synthesis of diazonium salts is historically an important transformation extensively utilized in dye manufacture. However the highly reactive nature of the diazonium functionality has additionally led to the development of many new reactions including several carbon-carbon bond forming processes. It is therefore highly desirable to determine optimum conditions for the formation of diazonium compounds utilizing the latest processing tools such as flow chemistry to take advantage of the increased safety and continuous manufacturing capabilities. Herein we report a series of flow-based procedures to prepare diazonium salts for subsequent in-situ consumption.

Mechanism for Broadband White-Light Emission from Two-Dimensional (110) Hybrid Perovskites.

The recently discovered phenomenon of broadband white-light emission at room temperature in the (110) two-dimensional organic-inorganic perovskite (N-MEDA)[PbBr4] (N-MEDA = N(1)-methylethane-1,2-diammonium) is promising for applications in solid-state lighting. However, the spectral broadening mechanism and, in particular, the processes and dynamics associated with the emissive species are still unclear. Herein, we apply a suite of ultrafast spectroscopic probes to measure the primary events directly following photoexcitation, which allows us to resolve the evolution of light-induced emissive states associated with white-light emission at femtosecond resolution. Terahertz spectra show fast free carrier trapping and transient absorption spectra show the formation of self-trapped excitons on femtosecond time-scales. Emission-wavelength-dependent dynamics of the self-trapped exciton luminescence are observed, indicative of an energy distribution of photogenerated emissive states in the perovskite. Our results are consistent with photogenerated carriers self-trapped in a deformable lattice due to strong electron-phonon coupling, where permanent lattice defects and correlated self-trapped states lend further inhomogeneity to the excited-state potential energy surface.

A Bismuth-Halide Double Perovskite with Long Carrier Recombination Lifetime for Photovoltaic Applications.

Despite the remarkable rise in efficiencies of solar cells containing the lead-halide perovskite absorbers RPbX3 (R = organic cation; X = Br(-) or I(-)), the toxicity of lead remains a concern for the large-scale implementation of this technology. This has spurred the search for lead-free materials with similar optoelectronic properties. Here, we use the double-perovskite structure to incorporate nontoxic Bi(3+) into the perovskite lattice in Cs2AgBiBr6 (1). The solid shows a long room-temperature fundamental photoluminescence (PL) lifetime of ca. 660 ns, which is very encouraging for photovoltaic applications. Comparison between single-crystal and powder PL decay curves of 1 suggests inherently high defect tolerance. The material has an indirect bandgap of 1.95 eV, suited for a tandem solar cell. Furthermore, 1 is significantly more heat and moisture stable compared to (MA)PbI3. The extremely promising optical and physical properties of 1 shown here motivate further exploration of both inorganic and hybrid halide double perovskites for photovoltaics and other optoelectronics.

Trapping of methylglyoxal by curcumin in cell-free systems and in human umbilical vein endothelial cells.

Curcumin, the most active compound of curcuminoids, has been shown to inhibit formation of advanced glycation end products (AGEs) in streptozotocin-induced diabetic rats. However, little is known on whether curcumin may trap methylglyoxal (MGO), a major reactive dicarbonyl compound, to inhibit AGE formation. We found that one molecule of curcumin effectively trapped one molecule of MGO at a 1:3 ratio at 24 h of incubation under physiological conditions (pH 7.4, 37 °C). Curcumin decreased N(ε)-(carboxymethyl)lysine (CML) expression in human umbilical vein endothelial cells. We further used two curcumin analogues, dimethoxycurcumin (DIMC) and ferulic acid, to investigate the possible MGO-trapping mechanism of curcumin. Results reveal that DIMC, but not ferulic acid, exhibited MGO-trapping capacity, indicating curcumin traps MGO at the electron-dense carbon atom (C10) between the two keto carbon groups. Thus, curcumin may prevent MGO-induced endothelial dysfunction by directly trapping MGO.

Photoswitched protein adsorption on electrostatically self-assembled azobenzene films.

Photoresponsive polymeric films fabricated by a facile electrostatic self-assembly technique are utilized to switch protein adsorption by light irradiation. The introduction of SiO(2) nanoparticles on the substrate results in a large reversible change of both wettability and protein adsorption.

Antimetastatic effects and mechanisms of apo-8'-lycopenal, an enzymatic metabolite of lycopene, against human hepatocarcinoma SK-Hep-1 cells.

Lycopene is primarily metabolized by carotenoid monoxygenase II into apo-8'- and apo-12'-lycopenal in the rat liver. Although lycopene possesses antimetastatic activity in a highly invasive hepatoma SK-Hep-1 cell line, little is known whether its metabolites have a similar effect. In this study, we investigated the antimetastatic effects of apo-8'-lycopenal (1-10 µM) in comparison with lycopene (10 µM) in SK-Hep-1 cells. We found that both apo-8'-lycopenal and lycopene inhibited the invasion and migration of SK-Hep-1 cells, and the effect of apo-8'-lycopenal was stronger than that of lycopene at the same concentration (10 µM). Mechanistically, apo-8'-lycopenal: 1) decreased the activities and protein expression of metalloproteinase-2 (MMP-2) and -9; 2) increased the protein expression of nm23-H1 and the tissue inhibitor of MMP (TIMP)-1 and -2; 3) suppressed protein expression of Rho small GTPases; and 4) inhibited focal adhesion kinase-mediated signaling pathway, such as ERK/p38 and PI3K-Akt axis. Overall, these results demonstrate that apo-8'-lycopenal possesses antimetastatic activity in SK-Hep-1 cells and that this effect is stronger than that of lycopene, suggesting that the antimetastatic effect may be attributed, at least in part, to its metabolites such as apo-8'-lycopenal.