Evolution of lowest singlet and triplet excited states with transition metals in group 10-12 metallaynes containing biphenyl spacer

A new series of thermally stable group 10 platinum(II) and group 12 mercury(II) poly-yne polymers containing biphenyl spacer trans-[-Pt(PBu₃)₂CC(p-C₆H₄)₂CC-]_n and [HgCC(p-C₆H₄)₂CC-]_n were prepared in good yields by Hagihara’s dehydrohalogenation reaction of the corresponding metal chloride precursors with 4,4′-diethynylbiphenyl HCC(p-C₆H₄)₂CCH at room temperature. We report the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic model complexes trans-[Pt(Ph)(PEt₃)₂CC(p-C₆H₄)₂CCPt(Ph)(PEt₃)₂] and [MeHgCC(p-C₆H₄)₂CCHgMe] as well as the group 11 gold(I) counterpart [(PPh₃)AuCC(p-C₆H₄)₂CCAu(PPh₃)]. The structural properties of all model complexes have been studied by X-ray crystallography. The influence of the heavy metal atom in these metal alkynyl systems on the intersystem crossing rate and the spatial extent of lowest singlet and triplet excitons is systematically characterized. Our investigations indicate that the organic triplet emissions can be harvested by the heavy-atom effect of group 10-12 transition metals (viz., Pt, Au, and Hg) which enables efficient intersystem crossing from the S₁ singlet excited state to the T₁ triplet excited state.     

Principal Submatrices of a Hermitian Matrix

Suppose k 1 ,<, k m and n are positive integers such that k 1 + … + k m h n . We characterize those k i × k i Hermitian matrices A i , i = 1, < , m that can appear as diagonal blocks of an n × n Hermitian matrix C with prescribed eigenvalues. The characterization will be given in terms of the eigenvalues of C and A i , i = 1, <, m . Our results extend those of Thompson and Freede, Horn, Fan and Pall.     

The electronic structure of the nitridoosmate(VIII) ion,OsO3N-

The electronic spectrum of the nitridoosmate(VIII) ion, OsO₃N^-, has been measured at liquid helium temperatures for thin films of the n-tetrabutyl-ammonium salt and for oriented, doped LiClO₄. 3H₂O single crystals. Four structured band systems, all individually composed of superimposed A ₁ ← A ₁ and E←A ₁ transitions, are observed at energies comparable to those of the two lowest ¹ T ₂←¹ A ₁ transitions of OsO₄. Prominent vibronic structure assigned to ν(Os-N) is observed for all of the bands. The bands are assigned to transitions to completely spin-orbit mixed states. The highest filled orbitals of OsO₃N^- are oxygen-localized and π non-bonding. The nitrido ligand appears to ‘dominate’ the π-bonding in the ion.     

Shear zones and wall slip in the capillary flow of concentrated colloidal suspensions

We image the flow of a nearly random close packed, hard-sphere colloidal suspension (a "paste") in a square capillary using confocal microscopy. The flow consists of a "plug" in the center while shear occurs localized adjacent to the channel walls, reminiscent of yield-stress fluid behavior. However, the observed scaling of the velocity profiles with the flow rate strongly contrasts yield-stress fluid predictions. Instead, the velocity profiles can be captured by a theory of stress fluctuations originally developed for chute flow of dry granular media. We verified this both for smooth and rough walls.     

Synthesis of Rhenabenzenes from the Reactions of Rhenacyclobutadienes with Ethoxyethyne

Treatment of Na[Re(CO)₅] with RC?CCO₂Et (R=phenyl, naphthalen‐1‐yl, phenanthren‐9‐yl and pyren‐1‐yl) followed by reaction with acetyl chloride and ethanol afforded the rhenacyclobutadienes Re{‐C(R)?C(CO₂Et)C(OEt)?}(CO)₄. Reactions of these rhenacyclobutadienes with HC?COEt produced rhenabenzenes Re{‐C(R)?C(CO₂Et)C(OEt)?CHC(OEt)?}(CO)₄. Except for R=Ph, new rhenacyclobutadienes with pendant alkenyl substituents Re{‐C(R)?C(C(OEt)?CH(CO₂Et))C(OEt)?}(CO)₄ were also isolated from these reactions. The NMR spectroscopic and X‐ray structural data, as well as the aromatic stabilization energy (ASE) values suggest that the rhenabenzenes are aromatic, with extensive delocalized π character.     

Nuclear magnetic resonance study of iron overload in liver tissue

Whole-tissue and homogenized samples of human liver were studied in a NMR spectrometer, T1 and T2 relaxation times were measured as a function of added inorganic or organic iron. When inorganic iron (Fe+3) was added, pronounced T1 and T2 shortening was noted. However, when organic iron, in the form of ferritin, was added, the amount of T1 and T2 relaxation enhancement was much reduced for the same amount of added iron. The in vitro ferritin results model the situation found in clinical studies of hemochromatosis. Only in cases of severe iron overload were significant decreases in relaxation times observed. The T2 relaxation time was the more reliable indicator of excessive levels of iron in the liver. The large range of T1 and T2 values encountered in normal volunteers precludes the use of MR to quantitatively measure iron levels in the liver. The T1 and T2 relaxation times measured at intervals for one individual tend to fluctuate as well, making the use of MR to follow the course of treatment of iron overload disorders unreliable.     

Fano resonances in prism-coupled square micropillars

We report Fano resonances in the frustrated total internal reflection (TIR) spectra of a prism-coupled square micropillar. Our angle-selective frustrated TIR technique reveals characteristically asymmetric resonance line shapes, which evolve spectrally over approximately a 2pi phase in the far field within a subdegree range of reflection angles. We theoretically model the asymmetric line shapes by the interference between a high-Q resonance that is evanescently coupled and partially confined by TIR, and a coherent background that is total internally reflected at the prism surface without coupling to the micropillar.     

First results from KamLAND: evidence for reactor antineutrino disappearance

KamLAND has measured the flux of nu;(e)'s from distant nuclear reactors. We find fewer nu;(e) events than expected from standard assumptions about nu;(e) propagation at the 99.95% C.L. In a 162 ton.yr exposure the ratio of the observed inverse beta-decay events to the expected number without nu;(e) disappearance is 0.611+/-0.085(stat)+/-0.041(syst) for nu;(e) energies >3.4 MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the "large mixing angle" region are excluded.     

Multimode resonances in square-shaped optical microcavities

Square-shaped two-dimensional optical microcavities (micro-cavities) were investigated for possible applications as filters for dense wavelength-division multiplexing. Multimode cavity resonances were observed in the elastic scattering of approximately 200-microm square-shaped micro-cavities in fused silica. Based on a two-dimensional k-space representation, we accounted for the multimode spectrum by different normal modes with rays confined by total internal reflection. The cavity-mode trajectories need not be closed after each round trip. Single-mode spectra are expected from smaller square-shaped micro-cavities.