Effect of axially projected oligothiophene pendants and nitro-functionalized diimine ligands on the lowest excited state in cationic Ir(III) bis-cyclometalates

The novel terthiophene (3T) oligomer 6 and a series of cationic Ir(III) bis-cyclometalates [Ir(C^N)(2)(N^N)]PF(6) 9-12 were prepared. The synthesis, characterization, electrochemical, and photophysical properties are reported. The cyclometalating ligands (C^N) are 2-phenylpyridinato (ppy) or the 3T oligomer (3T-ppy), asymmetrically capped in the 5 and 5" positions with the ppy and mesityl groups. The diimine ligands (N^N) are 2,2'-bipyridine (bpy) or 4-NO(2)-bipyridine (4-NO(2)-bpy). Hybrid metal-organic complexes 11 and 12 bear 3T-pendants ligated through the ppy cap, 10 and 12 contain NO(2) functionalized diimines, whereas 9 contains neither. Structural characterization of 10 by single crystal X-ray diffraction confirms the presence of the NO(2) substituent and pseudo-octahedral coordination geometry about the Ir(III) ion. Cyclic voltammetry highlights the large electron withdrawing effect of the NO(2) substituent, providing an 850 mV shift toward lower potentials for the first diimine centered reduction of 10 and 12. Strong overlap of the intense π → π* absorptions of the 3T-pendants with Ir(III) charge transfer bands is evident in complexes of 11 and 12, precluding the possibility for selective excitation of either chromophore. Photoexcitation (λ(ex) = 400 nm) of the series affords strong luminescence from the 3T oligomer 6 and the unsubstituted 9, with φ(em) = 0.11. In stark contrast the NO(2) and 3T functionalized complexes 10-12 display near total quenching of luminescence. Computations of the ground and excited state electronic structure using density functional theory (DFT) and time-dependent DFT (TD-DFT) indicate that both the NO(2) and 3T substituents play an important role in excited state deactivation of complexes 10-12. A substantial electronic contribution of the NO(2) substituent results in stabilization of the diimine based molecular orbital (MO) and offers an efficient nonradiative decay pathway for the excited state. Spin-orbit coupling effects of the Ir(III) ion lead to efficient population of the low lying, nonluminescent, triplet states centered on the 3T-pendants.     

Alpha-gamma decay studies of 255Rf, 251No and 247Fm

The decay of the isotopes ²⁵⁵Rf, ²⁵¹No and ²⁴⁷Fm produced in the reactions , and was investigated by means of α-γ spectroscopy. Previously observed γ transitions in coincidence with α decays of ²⁵⁵Rf were confirmed, their energies and line intensities were measured more precisely, and their multipolarities were determined as E1. In ²⁵¹No a new isomeric state at E ^* > 1700keV with a half-life of ≈ 2μs was identified. The decay of ²⁴⁷Fm was measured more precisely. A partial level scheme of the daughter nucleus ²⁴³Cf could be established.     

Anisotropy in Langmuir layers of a bent-core liquid crystal

Langmuir layers of a symmetric bent-core molecule with hydrocarbon end chains and two chlorine atoms substituted on the central phenyl ring of the bent core were characterized by a combination of surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. These layers were found to be optically anisotropic, in contrast to Langmuir layers of similar molecules with different substitutions on the core. After compression, the orientation of the optical axis was essentially uniform over the film. Upon decompression, the film broke into uniform islands or domains. Measuring domain reflectivity while changing the domain orientation allowed the determination of the tilt angle with respect to both domain features and the film normal, as well as the refractive index anisotropy. The tilt angle, near 90 degrees, suggests that the bent-core molecules lie quite flat on the surface.     

Exploration of ground and excited electronic states of aromatic and quinoid S,S-dioxide terthiophenes. Complementary systems for enhanced electronic organic materials

We analyze the electronic and molecular structures for the ground and excited electronic states of aromatic terthiophene (3T), the quinodimethane 3',4'-dibutyl-5,5' '-bis(dicyanomethylene)-5,5' '-dihydro-2,2':5',2' '-terthiophene (3Q), and isologues with the middle ring S-oxidized (3TO2, 3QO2). These represent extremes of electron rich and deficient ground states, often exhibiting complementary properties. Oxidizing the central sulfur atom affects the molecular structure, electron affinity, and photophysical properties of both pi systems. The consequences for 3T include de-aromatization of the central thiophene, red-shifting of the electronic absorption spectrum, and lowering of the reduction potential. The electron deficient quinoid 3QO2 shows an enhancement of electron affinity from reducing the electron-donor ability of sulfur, and a blue-shifting of its electronic absorption spectrum was seen. Fluorescence emission is quenched in the sulfonated terthiophene, and the contrary effect again would be expected upon sulfonation of a quinoid emitter. Raman vibrational spectroscopy, electrochemistry, and UV-vis and fluorescence spectroscopies are analyzed in conjunction with theoretical calculations.     

Computational principles of determining and improving mass precision and accuracy for proteome measurements in an Orbitrap

Precision proteomics requires high-resolution and high mass accuracy peptide measurements. The Orbitrap instrument achieves excellent resolution on a chromatographic time scale and its design is favorable for very high mass accuracy. Here we describe how mass precision for each peptide increases successively by considering all associated measurements, starting from the MS peak and proceeding to its chromatographic elution profile, isotope envelope, and stable isotope pair in SILAC measurements. We extract peptide charge pairs to perform nonlinear recalibration of the Orbitrap mass scale through spline interpolation. The deviation of mass values determined from charge pairs is used to convert mass precision to mass accuracy for subsequent database search. The corrected mass precision is consistent with the mass accuracy independently determined by database identification. Individual mass deviations range from below 100 ppb for peptides with many associated mass measurements and good signal intensities to low ppm for peptides with few mass measurements and signals close to the noise level. This extremely high and individualized mass accuracy is equivalent to a substantial increase in database identification score.     

On non-solvable Camina pairs

In this paper we study non-solvable and non-Frobenius Camina pairs (G,N). It is known [D. Chillag, A. Mann, C. Scoppola, Generalized Frobenius groups II, Israel J. Math. 62 (1988) 269–282] that in this case N is a p-group. Our first result (Theorem 1.3) shows that the solvable residual of G/O_p(G) is isomorphic either to SL(2,p^e),p is a prime or to SL(2,5), SL(2,13) with p=3, or to SL(2,5) with p7.Our second result provides an example of a non-solvable and non-Frobenius Camina pair (G,N) with |O_p(G)|=5⁵ and G/O_p(G)SL(2,5). Note that G has a character which is zero everywhere except on two conjugacy classes. Groups of this type were studies by S.M. Gagola [S.M. Gagola, Characters vanishing on all but two conjugacy classes, Pacific J. Math. 109 (1983) 363–385]. To our knowledge this group is the first example of a Gagola group which is non-solvable and non-Frobenius.     

K3(Sc0.875Nb0.125)Nb2O9H1.75: a new scandium niobate with a unique cage structure

Potassium scandium niobate hydroxide, K₃(Sc_0.875Nb_0.125)Nb₂O₉H_1.75, is a new scandium niobate with a unique cage structure. The structure contains two non‐equivalent K⁺ sites (3m and m2 site symmetry), one disordered Sc³⁺/Nb⁵⁺ site (m site symmetry), one Nb⁵⁺ site (3m site symmetry), two O²⁻ sites (m and mm2 site symmetry) and one H⁺ site (m site symmetry). Both scandium and niobium have octahedral environments, which combine to form cages around potassium. One K atom lies in a cube‐like cage built of seven octahedra, while the other K atom is encapsulated by an eight‐membered trigonal face‐bicapped prism. The cages form sheets that extend along the ab plane.     

原子尺度的欧姆表

一种高度稳定的扫描隧道显微镜(STM)可以在小于原子尺度范围精密测量金属的电学性能。扫描隧道显微镜可以在表面对单个原子成像,或者移动单个原子。研究人员最近进一步提高了这个仪器的精确性,可以对铅表面单个原子附近不同位置的电导进行测量。这个结果或许有助于揭示金属和超导体的性质的差异,未来或许可以用于纳米加工技术。一台STM的探针非常尖锐,尖端只有一个原子,将探针在真空中操控到距离表面极近的位置。电子可以在加有电势的间隙之间越过,或者称隧穿。当探针在表面运动时,记录通过探针的电流可以对表面成像。另外一种STM技术是将探针保持与表面接触,使得探针原子与样品表面形成化学键。研究人员使用这种被称为点接触技术,可以测量一种材料原子尺度的电导性质,了解在量子物理中电流是如何流动的,此时传统的欧姆定律不再成立。     

Defect orientation on the chain folded surfaces of two-arm poly(ethylene oxide) lamellar crystals

Two-arm poly(ethylene oxide) fractions (PEOs) with arm lengths of 2 220 g/mol were synthesized via a reaction using terephthaloyl (1,4-), isophthaloyl (1,3-) and phthaloyl (1,2-) dichorides as coupling agents. The center of each molecule thus includes a phenylene group as a configurational defect, and they are excluded to the crystal folded basal surfaces. In the lamellar crystals with the once-folded overall molecular conformation, observations of surface-enhanced Raman scattering experiments show that only the in-plane vibration modes are selectively enhanced. This implies that the arrangement of phenylene groups adopts a “stand-up” orientation on the basal surface, i. e., the π plane of phenylene groups in the defects is perpendicular to the lamellar basal surface.