Ligand-supported palladium-catalyzed cross-coupling reactions of (hetero) aryl chlorides

The introduction of electron rich and sterically hindered ligands has made otherwise inert aryl chlorides and hetero aryl chlorides viable coupling partners in palladium-catalyzed Suzuki-Miyaura, Sonogashira, Stille and other types of cross-coupling reactions. This review gives highlights of cross-coupling of aryl chlorides employing in situ generated palladium catalytic systems.     

Modulating the light switch by (3)MLCT-(3)ππ* state interconversion

The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: λ(max) = 393 nm) upon substitution at the terminal phenyl groups (2: λ(max) = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at λ(max) = 450 nm are observed for [Ru(phen)(2)bptt](2+)(3) and [Ru(phen)(2)tbptt](2+)(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy)(3)](2+) and [Ru(phen)(3)](2+), indicating that the MLCT excited state is primarily localized within the [Ru(phen)(3)](2+) manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: ?(H(2)O) = 0.005, 4: ?(H(2)O) = 0.011) and biexponential decay kinetics (3: τ(1) = 40 ns, τ(2) = 230 ns; 4: τ(1) ～ 26 ns, τ(2) = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield (?(DNA) = 0.045), while the quantum yield of 4 is relatively unaffected (?(DNA) = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (K(b) = 3.3 × 10(4) M(-1)). The origin of this light switch behavior involves two competing (3)MLCT states similar to that of the extensively studied light switch molecule [Ru(phen)(2)dppz](2+). The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the (3)ππ* excited state into competition with the emitting (3)MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments.     

Polyglycerol-derived amphiphiles for the solubilization of single-walled carbon nanotubes in water: a structure-property study

A series of nonionic amphiphiles derived from polyglycerol dendrons were studied for their ability to solubilize and isolate single-walled carbon nanotubes. The amphiphiles possessed differently sized polar head groups, hydrophobic tail units, and various aromatic and non-aromatic groups between the head and tail groups. Absorbance analysis revealed that amphiphiles with anchor groups derived from pyrene were far inferior to those that possessed simple linear aliphatic tail groups. Absorbance and near-infrared fluorescence analyses revealed a weak dependence on the dendron size of the head group, but a strong positive trend in suspended nanotube density and fluorescence intensity for amphiphiles with longer tail units. Variations in the moieties linking the head and tail groups led to a range of effects on the suspensions, with linkers imparting flexibility and a bent shape that gave improved performance overall. This was illustrated most dramatically by a pair of benzamide-containing amphiphiles, the para isomer of which showed evidence in the fluorescence data of increased nanotube aggregate formation when compared with the meta isomer. In addition, statistical AFM was used to illustrate more directly the microscopic differences between amphiphiles that were effective at nanotube bundle disruption and those that were not.     

Production and validation of model iron-tannate dyed textiles for use as historic textile substitutes in stabilisation treatment studies

Adsorption of methylene blue (MB) on agar was investigated as a function of temperature (308-328 K), different concentrations of NaCl and HCl and various weight percentages of binary mixtures of ethanol with water. It was observed that the maximum experimental adsorption capacity, q _{m, exp}, in water is up to 50 mg g^-1 and decreases with increase in weight percentage of ethanol and NaCl and HCl concentration compared to that of water. Analysis of data using ARIAN model showed that MB adsorbs as monomer and dimer on the surface of agar. Binding constants of MB to agar were calculated using the Temkin isotherm. The process is exothermic in water and other solutions. The mean adsorption energy (E) value indicated binding of MB to agar is chemical adsorption. Kinetics of this interaction obeys from the pseudo-second-order model and diffusion of the MB molecules into the agar is the main rate-controlling step.     

A Linear Ion Trap with an Expanded Inscribed Diameter to Improve Optical Access for Fluorescence Spectroscopy

We report a custom-geometry linear ion trap designed for fluorescence spectroscopy of gas-phase ions at ambient to cryogenic temperatures. Laser-induced fluorescence from trapped ions is collected from between the trapping rods, orthogonal to the excitation laser that runs along the axis of the linear ion trap. To increase optical access to the ion cloud, the diameter of the round trapping rods is 80% of the inscribed diameter, rather than the roughly 110% used to approximate purely quadrupolar electric fields. To encompass as much of the ion cloud as possible, the first collection optic has a 25.4 mm diameter and a numerical aperture of 0.6. The choice of geometry and collection optics yields 10⁷ detected photons/s from trapped rhodamine 6G ions. The trap is coupled to a closed-cycle helium refrigerator, which in combination with two 50 Ohm heaters enables temperature control to below 25 K on the rod electrodes. The purpose of the instrument is to broaden the applicability of fluorescence spectroscopy of gas-phase ions to cases where photon emission is a minority relaxation pathway. Such studies are important to understand how the microenvironment of a chromophore influences excited state charge transfer processes.

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Supramolecular Nested Microbeads as Building Blocks for Macroscopic Self‐Healing Scaffolds

The ability to construct self‐healing scaffolds that are injectable and capable of forming a designed morphology offers the possibility to engineer sustainable materials. Herein, we introduce supramolecular nested microbeads that can be used as building blocks to construct macroscopic self‐healing scaffolds. The core–shell microbeads remain in an “inert” state owing to the isolation of a pair of complementary polymers in a form that can be stored as an aqueous suspension. An annealing process after injection effectively induces the re‐construction of the microbead units, leading to supramolecular gelation in a preconfigured shape. The resulting macroscopic scaffold is dynamically stable, displaying self‐recovery in a self‐healing electronic conductor. This strategy of using the supramolecular assembled nested microbeads as building blocks represents an alternative to injectable hydrogel systems, and shows promise in the field of structural biomaterials and flexible electronics.     

Physicochemical and thermal effects of pendant groups,spatial linkages and bridging groups on the formation and processing of polyimides

Aromatic polyimides are known for their remarkable thermal and chemical properties which are greatly influenced by their precursors. In this study, we report synthesis and characterization of four different aromatic polyimides. The four different dianhydrides (ODPA, BTDA, BPDA, and PMDA) were reacted with a diamine (BisAPAF) via azeotropic imidization under same conditions. FTIR analysis confirmed the formation of aromatic polyimides and all but one polyimide (HPI-BPDA) were found to be completely soluble in common solvents. The obtained molecular weights were between 16,000 and 32,000?g/mol, glass transition temperatures were between 250?°C and 275?°C, degradation temperatures were above 550?°C, and the d-spacing values were around 5?Å. These properties are promising and can be beneficial for various applications such as thin films and membranes.