Synthesis and fluorescence spectra of oxa[3.n]phenanthrenophanes

[reaction: see text]. Novel photostable oxa[3.n](3,9)- and [3.3](3,10)phenanthrenophanes (n = 3, 4) bearing trimethylene-type linkage(s) were successfully synthesized by the intramolecular acid-catalyzed etherification of the corresponding precursor diols. syn-Oxa[3.3](3,10)phenanthrenophane afforded the most red-shifted excimer fluorescence (lambda(max) = 432 nm) among the phenanthrenophanes so far prepared.     

New source of dense, cryogenic positron plasmas

We have developed a new method, based on the ballistic transfer of preaccumulated plasmas, to obtain large and dense positron plasmas in a cryogenic environment. The method involves transferring plasmas emanating from a region with a low magnetic field (0.14 T) and relatively high pressure (10(-9) mbar) into a 15 K Penning-Malmberg trap immersed in a 3 T magnetic field with a base pressure better than 10(-13) mbar. The achieved positron accumulation rate in the high field cryogenic trap is more than one and a half orders of magnitude higher than the previous most efficient UHV compatible scheme. Subsequent stacking resulted in a plasma containing more than 1.2 x 10(9) positrons, which is a factor 4 higher than previously reported. Using a rotating wall electric field, plasmas containing about 20 x 10(6) positrons were compressed to a density of 2.6 x 10(10) cm(-3). This is a factor of 6 improvement over earlier measurements.     

Direct observation of chiral susceptibility in the canonical spin glass AuFe

The extraordinary Hall resistivity rho(xy) and the magnetization M of a canonical spin glass AuFe (8 at.% Fe) were measured simultaneously as functions of temperature with the best care to the thermal and the magnetic field hysteresis. The data of rho(xy) show an anomaly at the spin glass transition temperature T(g) and have different zero field cooling (ZFC) and field cooling (FC) measurements below T(g). Moreover, the value of rho(xy)/M, which represents the chiral susceptibility of the system in the present case, also shows the difference between ZFC and FC measurements. The results are consistent with the predictions of the chirality scenario of canonical spin glasses by Kawamura.     

Electronically promoted Payne rearrangement of 3-CF3-2,3-epoxyalcohols

[reaction: see text] Smooth and selective Payne rearrangement was achieved for the above types of epoxyalcohols with a CF(3) group so as to form thermodynamically more stable alkoxides, where the strongly electron-withdrawing nature of this moiety played a significantly important role and was proved to overcome increased steric instability of epoxides from syn-E to anti-Z isomers.     

Sigmasigma* transition in anti,cisoid alternating oligosilanes: clear-cut evidence for suppression of conjugation effect by a cisoid turn

On the basis of the UV absorption spectra of the anti,cisoid alternating oligosilanes, the first experimental clear-cut evidence was presented for the generally accepted idea that the sigma conjugation in polysilanes does not effectively extend through a tetrasilane fragment with a small dihedral angle such as a cisoid turn.