Synthesis of B/Si bidentate Lewis acids, o-(Fluorosilyl)(dimesitylboryl)benzenes, and their fluoride ion affinity

o-(Fluorosilyl)(dimesitylboryl)benzenes have been prepared as colorless crystals by reacting fluorodimesitylborane with o-(fluorodimethylsilyl)phenyllithium and o-(fluorodiphenylsilyl)phenyllithium. The o-(fluorosilyl)(dimesitylboryl)benzenes serve as B/Si bidentate Lewis acid and efficiently capture fluoride ion from potassium fluoride in the presence of [2.2.2]cryptand or 18-crown-6 in toluene, giving the corresponding mu-fluoro bridged products. The structures were characterized by X-ray crystal structure analysis and multinuclear NMR spectroscopy. Fluoride ion affinities of the o-(fluorosilyl)(dimesitylboryl)benzenes were evaluated in comparison with non-silylated triarylborane.     

OFF-OFF-ON switching of fluorescence and electron transfer depending on stepwise complex formation of a host ligand with guest metal ions

Stepwise complex formation is observed between 2,3,5,6-tetrakis(2-pyridyl)pyrazine (TPPZ) and a series of metal ions (M(n+) = Sc3+, Y3+, Ho3+, Eu3+, Lu3+, Nd3+, Zn2+, Mg2+, Ca2+, Ba2+, Sr2+, Li+), where TPPZ forms a 2:1 complex [(TPPZ)2-M(n+)] and a 1:1 complex [TPPZ-M(n+)] with Mn+ at low and high concentrations of metal ions, respectively. The fluorescence intensity of TPPZ begins to increase at high concentrations of metal ions, when the 2:1 (TPPZ)2-M(n+) complex is converted to the fluorescent 1:1 TPPZ-M(n+) complex. This is regarded as an "OFF-OFF-ON" fluorescence sensor for metal ions depending on the stepwise complex formation between TPPZ and metal ions. The fluorescence quantum yields of the TPPZ-M(n+) complex vary depending on the metal valence state, in which the fluorescence quantum yields of the divalent metal complexes (TPPZ-M2+) are much larger than those of the trivalent metal complexes (TPPZ-M3+). On the other hand, the binding constants of (TPPZ)2-M(n+) (K1) and TPPZ-M(n+) (K2) vary depending on the Lewis acidity of metal ions (i.e., both K1 and K2 values increase with increasing Lewis acidity of metal ions). Sc3+, which acts as the strongest Lewis acid, forms the (TPPZ)2-Sc3+ and TPPZ-Sc3+ complexes stoichiometrically with TPPZ. In such a case, "OFF-OFF-ON" switching of electron transfer from cobalt(II) tetraphenylporphyrin (CoTPP) to O2 is observed in the presence of Sc3+ and TPPZ depending on the ratio of Sc3+ to TPPZ. Electron transfer from CoTPP to O2 occurs at Sc3+ concentrations above the 1:2 ratio ([Sc3+]/[TPPZ]0 > 0.5), when the (TPPZ)2-Sc3+ complex is converted to the TPPZ-Sc3+ complex and TPPZ-(Sc3+)2, which act as promoters of electron transfer (ON) by the strong binding of O2*- with Sc3+. In sharp contrast, no electron transfer occurs without metal ion (OFF) or in the presence at Sc3+ concentrations below the 1:2 ratio (OFF), when the (TPPZ)2-Sc3+ complex has no binding site available for O2*-.     

Synthetic Control of the Excited‐State Dynamics and Circularly Polarized Luminescence of Fluorescent “Push–Pull” Tetrathia[9]helicenes

A series of fluorescent “push‐pull” tetrathia[9]helicenes based on quinoxaline (acceptor) fused with tetrathia[9]helicene (donor) derivatives was synthesized for control of the excited‐state dynamics and circularly polarized luminescence (CPL) properties. In this work, introduction of a quinoxaline onto the tetrathia[9]helicene skeleton induced the “push–pull” character, which was enhanced by further introduction of an electron‐releasing Me₂N group or an electron‐withdrawing NC group onto the quinoxaline unit (denoted as Me₂N‐QTTH and NC‐QTTH, respectively). These trends were successfully discussed in terms of by electrochemical measurements and density functional theory (DFT) calculations. As a consequence, significant enhancements in the fluorescence quantum yields (Φ_FL) were achieved. In particular, the maximum Φ_FL of Me₂N‐QTTH was 0.43 in benzene (NC‐QTTH: Φ_FL=0.30), which is more than 20 times larger than that of a pristine tetrathia[9]helicene (denoted as TTH; Φ_FL=0.02). These enhancements were also explained by kinetic discussion of the excited‐state dynamics such as fluorescence and intersystem crossing (ISC) pathways. Such significant enhancements of the Φ_FL values thus enabled us to show the excellent CPL properties. The value of anisotropy factor g_CPL (normalized difference in emission of right‐handed and left‐handed circularly polarized light) was estimated to be 3.0×10^?3 for NC‐QTTH.     

Visualization of cancer‐related chemical components in mouse pancreas tissue by tapping‐mode scanning probe electrospray ionization mass spectrometry

Mass spectrometry imaging is an informative approach for the comprehensive analysis of multiple components inside biological specimens. We used novel tapping‐mode scanning probe electrospray ionization mass spectrometry method to visualize cancer‐related chemical components in the mouse pancreas tissue section at a sampling pitch of 100 µm. Positive ion mode measurements from m/z 100 to 1500 resulted in the visualization of multiple components that are tentatively assigned as polyamines, lipids and proteins. Their signal intensities inside the cancerous and the non‐cancerous regions were found to be significantly different by the two‐sample t‐test. Copyright © 2015 John Wiley & Sons, Ltd.     

Total Synthesis of Dictyodendrins by the Gold-Catalyzed Cascade Cyclization of Conjugated Diynes with Pyrroles

In total and formal syntheses of dictyodendrins B, C, E, and F, the key step involved the direct construction of the pyrrolo[2,3-c]carbazole core by the gold-catalyzed annulation of a conjugated diyne with a pyrrole to form three bonds and two aromatic rings. The subsequent introduction of substituents at the C1 (Suzuki–Miyaura coupling), C2 (addition to an aldehyde), N3 (alkylation), and C5 positions (Ullman coupling) provided divergent access to dictyodendrins.     

Synthesis of bithiazole‐based crystalline polymers via palladium‐catalyzed direct CH arylation

Palladium‐catalyzed direct arylation polycondensation afforded a bithiazole‐based homopolymer and donor–acceptor (D–A)‐type copolymers where the bithiazole unit served as an acceptor unit. The results of polymerization strongly depended on the solubility of the polymers; long alkyl chain substituents were required for the formation of high‐molecular‐weight polymers in high yields owing to low solubility of the bithiazole‐based polymers. X‐ray diffraction studies revealed that the obtained polymers were highly crystalline. In particular, a well‐ordered lamellar structure was observed in the D–A‐type copolymer with flexible alkyl chains after thermal annealing, presumably owing to the combination of interchain interactions between the bithiazole units and the electrostatic D–A interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1396–1402     

Anion conductive aromatic polymers containing fluorenyl groups: Effect of the position and number of ammonium groups

Synthesis and properties of anion conductive aromatic block copolymers, QPE‐bl‐3, QPE‐bl‐3 M2, and M4, containing fluorenylidene biphenylene groups as scaffold for ammonium groups are described. These copolymers share the same main chain structure, but the position and the number of ammonium groups on a fluorenyl group differ. High molecular weight quaternized block copolymers were obtained via typical chloromethylation reaction or using preaminated monomers, and were well‐characterized by ¹H NMR spectra. Self‐standing bendable membranes were obtained by solution casting. QPE‐bl‐3 M4 membranes containing four ammonium groups per hydrophilic repeat unit (highest ammonium density) in the hydrophilic block exhibited well developed phase‐separated morphology, while QPE‐bl‐3 membranes containing two ammonium groups per hydrophilic repeat unit exhibited high anion conductivity. The highest anion conductivity (104 mS/cm) was obtained with QPE‐bl‐3 membrane (IEC = 2.1 meq/g) at 80 °C in water. An H₂/O₂ alkaline fuel cell was operable with the membrane to achieve 62 mW/cm² of the maximum power density at 161 mA/cm² of the current density. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 935–944     

Solid-state structure and optical properties of highly fluorescent diketopyrrolopyrrole derivatives synthesized by cross-coupling reaction

Diketopyrrolopyrrole (DPP) derivatives with four different substituents were synthesized by cross-coupling reactions. The DPP derivatives were investigated in terms of their solid-state structure, absorption, emission, and electrochemistry. The electron-donating property of each substituent causes a redshift of UV/vis absorption and emission in the solution state. Although all of the DPP derivatives have high quantum yields in solution, only butoxyphenyl-substituted DPP exhibits strong emission in the solid state.     

Surface tension and viscosity of molten vanadium measured with an electrostatic levitation furnace

Surface tension and viscosity of molten vanadium were measured over a wide temperature range by the oscillating drop method in an electrostatic levitation furnace. Over the (2023 to 2517) K temperature range, the surface tension can be expressed as γ(T)/(10^?3 N/m) = 1935 ? 0.27 {(T ? T_m)/K} with T_m = 2183 K. Over the same temperature span, the viscosity can be expressed as η(T)/(10^?3 Pa · s) = 1.23exp[2.27 · 10⁴/(RTK^?1)], where R is the gas constant.     

Luminescent Ir(III) complexes containing benzothiazole-based tridentate ligands: synthesis, characterization, and application to organic light-emitting diodes

Ir(III) complexes that contain benzothiazole-based tridentate ligands were synthesized and their crystal structures and luminescent properties were examined. A neutral complex had a high quantum yield (89%) and performed well as an emissive material for organic light-emitting diodes.