Phosphorescent iridium(III) complexes with nonconjugated cyclometalated ligands

A series of blue phosphorescent iridium(III) complexes 1-4 with nonconjugated N-benzylpyrazole ligands were synthesized and their structural, electrochemical, and photophysical properties were investigated. Complexes 1-4 exhibit phosphorescence with yields of 5-45 % in degassed CH2Cl2. Of the compounds, 1 showed emission that was nearly true blue at 460 nm with a lack of vibronic progression. These photophysical data clearly demonstrate that the methylene spacer of the cyclometalated N-benzylpyrazole chelate effectively interrupts the pi conjugation upon reacting with a third L X chelating chromophore. This gives a feasible synthesis for the blue phosphorescent complexes with a sufficiently large energy gap. In another approach, these complexes were investigated for their suitability for the host material in phosphorescent OLEDs. The device was synthesized by using 1 as the host for the green-emitting [Ir(ppy)3] dopant, which exhibits an external quantum conversion efficiency (EQE) of up to 11.4 % photons per electron (and 36.6 cdA(-1)), with 1931 Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.59), a peak power efficiency of 21.7 lmW(-1), and a maximum brightness of 32000 cdm(-2) at 14.5 V. At the practical brightness of 100 cdm(-2), the efficiency remains above 11 % and 18 lmW(-1), demonstrating its great potential as the host material for phosphorescent organic light-emitting diodes.     

Formal Total Synthesis of (+)‐Cortistatins A and J

An efficient formal total synthesis of (+) cortistatins A and J has been accomplished, by exploiting a highly diastereoselective intramolecular [4+3] cycloaddition of epoxy enolsilanes as the key reaction to construct rings B and C of the cortistatins in one step.     

Fabrication of Electrospun Polymer Fibers with Nonspherical Cross‐Sections Using a Nanopressing Technique

The fabrication of electrospun polymer fibers is demonstrated with anisotropic cross‐sections by applying a simple pressing method. Electrospun polystyrene or poly(methyl methacrylate) fibers are pressed by flat or patterned substrates while the samples are annealed at elevated temperatures. The shapes and morphologies of the pressed polymer fibers are controlled by the experimental conditions such as the pressing force, the pressing temperature, the pressing time, and the surface pattern of the substrate. At the same pressing force, the shape changes of the polymer fibers can be controlled by the pressing time. For shorter pressing times, the deformation process is dominated by the effect of pressing and fibers with barrel‐shaped cross‐sections can be generated. For longer pressing times, the effect of wetting becomes more important and fibers with dumbbell‐shaped cross‐sections can be obtained. Hierarchical polymer fibers with nanorods are fabricated by pressing the fibers with porous anodic aluminum oxide templates.

     

Computer diagnosis system for thermal analysis of engine piston

This study presents a finite element heat-transfer model for the prediction of piston temperature distributions in a real time operation engine. The thermal boundary conditions are specified adequately in the model for various operations. The time-mean, area-averaged gas temperature and heat transfer coefficient could be obtained from the engine simulation. The ambient tremperatures along piston ring belt and skirt were estimated with a formula and the corresponding heat transfer coefficients were evaluated through equivalent thermal circuit analysis. The model is also calibrated and the predicted and measured temperatures compared for the operating engine. The predictions are reasonable, providing confidence in the use of the simulation model.     

Micropatch‐arrayed pads for non‐invasive spatial and temporal profiling of topical drugs on skin surface

Micropatch‐arrayed pads (MAPAs) are presented as a facile and sensitive sampling method for spatial profiling of topical agents adsorbed on the surface of skin. MAPAs are 28 × 28 mm sized pieces of polytetrafluoroethylene containing plurality of cavities filled with agarose hydrogel. They are affixed onto skin for 10 min with the purpose to collect drugs applied topically. Polar compounds are absorbed by the hydrogel micropatches. The probes are subsequently scanned by an automated nanospray desorption electrospray ionization mass spectrometry system operated in the tapping dual‐polarity mode. When the liquid junction gets into contact with every micropatch, polar compounds absorbed in the hydrogel matrix are desorbed and transferred to the ion source. A 3D‐printed interface prevents evaporation of hydrogel micropatches assuring good reproducibility and sensitivity. MAPAs have been applied to follow dispersion of topical drugs applied to human skin in vivo and to porcine skin ex vivo, in the form of self‐adhesive patches. Spatiotemporal characteristics of the drug dispersion process have been revealed using this non‐invasive test. Differences between drug dispersion in vivo and ex vivo could be observed. We envision that MAPAs can be used to investigate spatiotemporal kinetics of various topical agents utilized in medical treatment. Copyright © 2015 John Wiley & Sons, Ltd.     

Microhydration Effects on the Ultrafast Photodynamics of Cytosine: Evidences for a Possible Hydration‐Site Dependence

Ultrafast excited‐state deactivation dynamics of small cytosine (Cy) and 1‐methylcytosine (1mCy) microhydrates, Cy?(H₂O)_1‐3 and 1mCy?(H₂O)_1,2, produced in a supersonic expansion have been studied by mass‐selected femtosecond pump–probe photoionization spectroscopy at about 267 nm excitation. The seeded supersonic expansion of Ar/H₂O gas mixtures allowed an extensive structural relaxation of Cy and 1mCy microhydrates to low‐energy isomers. With the aid of electronic structure calculations, we assigned the observed ultrafast dynamics to the dominant microhydrate isomers of the amino‐keto tautomer of Cy and 1mCy. Excited‐state lifetimes of Cy?(H₂O)_1‐3 measured here are 0.2–0.5 ps. Comparisons of the Cy?H₂O and 1mCy?H₂O transients suggest that monohydration at the amino Watson–Crick site induces a substantially stronger effect than at the sugar‐edge site in accelerating excited‐state deactivation of Cy.     

Light-induced crosslinkable semiconducting polymer dots

This paper describes a synthetic approach for photocrosslinkable polyfluorene (pc-PFO) semiconducting polymer dots, and demonstrates their superior ability to crosslink and form 3-D intermolecular polymer networks. The crosslinked pc-PFO Pdots are equipped with excellent encapsulating ability of functional small molecules. Optimum conditions of light irradiation on pc-PFO Pdots were investigated and clarified by using polymer thin films as a model. By employing the optimal light irradiation conditions, we successfully crosslinked pc-PFO Pdots and studied their particle sizes, photophysical, and colloidal properties. Single-particle imaging and dynamic-light-scattering measurements were conducted to understand the behaviors of photocrosslinked Pdots. Our results indicate pc-PFO Pdots can be easily photocrosslinked and the crosslinked species have excellent colloidal stability, physical and chemical stability, fluorescence brightness, and specific binding properties for cellular labeling. Considering that optical stimulus can work remotely, cleanly, and non-invasively, this study should pave the way for a promising approach to further develop stimuli-responsive ultrabright and versatile Pdot probes for biomedical imaging.     

An Overview of Recent Advances in the Synthesis of Organic Unsymmetrical Disulfides

Organic unsymmetrical disulfides have been extensively applied in various academic and industrial fields including intermediates in organic synthesis, agriculture, and food science, natural materials, biochemistry, pharmaceutical and medicine chemistry, polymers, material engineering, etc. They play a crucial role in the fabrication of various biological active sulfur heterocycles. Due to broad and extensive applications, many methods have been developed for the synthesis of unsymmetrical S−S and efforts have been made to improve some issues such as cost, energy efficiency, green chemistry, avoid or minimizing waste generation. Several outstanding review articles have been previously published highlighting the advances of S−S bond formation, in general, using various reagents under different conditions in the absence or presence of oxidants/catalysts. In 2020, a review paper was published by our group focusing on recent developments since 2014 in the synthesis of organic symmetrical disulfides. However, investigations on new catalytic methods are being regularly reported and new types of unsymmetrical disulfides are synthesized. The present overview has attempted to systematically summarize recent advances in the process of unsymmetrical S−S bond formation with a major focus since 2010, highlighting mechanistic considerations, substrate scope, advantages, and limitations. The patents are not studied in this overview.     

The Decomposition Reaction of 4‐Acetylsydnones Arylhydrazones

The acidic decomposition of 4‐acetylsydnones arylhydrazones 2 results in the formation of 4‐arylhydrazo‐1,2‐pyrazolin‐5‐ones 3 and 4‐arylamino‐1,2,3‐triazoles 4 , respectively. The reactions of 4‐acetylsydnones 1 with arylhydrazines 5 afford compounds 3 as the only products in the absence of solvent.