No abstract

No abstract

Producing supramolecular chirality from achiral π-conjugated polymers toward preferred chiral memory, effective circularly polarized luminescence, and chiral sensor is extremely important in design of functional chiral materials. Proposed herein is an effective protocol to generate and memorize the supramolecular chirality formed from achiral poly­(9,9-dioctyl­fluorene) (PF8) induced by chiral solvation. The process of chiral supramolecular assembly was monitored by UV–vis spectroscopy, circular dichroism (CD), and fluorescent spectroscopy. Achiral PF8 dissolved in neat (R)-(+)-limonene (1R) and (S)-(−)-limonene (1S) underwent chiral sol–gel transition at −20 °C. PF8 aggregates revealed intense CD and circularly polarized luminescence (CPL) signals due to β-phase, exhibiting absolute dissymmetry ratio of ≈2 × 10–3 at 430–470 nm. The supramolecular chirality of PF8 aggregates can be perfectly memorized in solid film even near decomposition temperature (300 °C), comparing favorably with that from chiral polyfluorene. Atomic force microscopy (AFM) inferred helically distorted PF8 aggregate motifs responsible for the CD and CPL functionality. Furthermore, the first chiral sensor to detect nonracemic limonene molecules employing achiral PF8 spin-cast film from CHCl3 solution was achieved.

No abstract

oxides for this reaction appears to correlate with basicity, with no dependence on variable cation valencies or lattice oxygen mobilities as appears to be significant for some other reactions, such as CO oxidation, on these materials.49 Accordingly, in a mechanistic study by Minachev et it was proposed that hydrogen dissociation can occur due to the polarizing action of a rare-earth cation and an oxygen ion and is the rate-limiting step in C2H4 hydrogenation on these materials. On the basis of a series of isotopic studies on Dy203 at 220 K, Minachev et al. further proposed that ethylene is associatively adsorbed on the oxide surface and that the reaction proceeds via a semihydrogenated C2H4 (adsorbed) complex. This catalytic activity of the rare-earth oxides toward C2H4 hydrogenation does not necessarily contradict our observation of the absence of molecular adsorption of C2H4 on oxidized Gd under UHV conditions, because the correlation between the strength of adsorption and hydrogenation activity is unknown.Accordingly, two areas for further investigation are indicated. First, studies of the catalytic activity of rare earth oxide surfaces toward acetylene hydrogenation are necessary for comparison with studies of ethylene hydrogenation. Second, investigations by other techniques, especially vibrational spectroscopy, of the structure of the C2H2 moiety adsorbed on oxidized rare-earth surfaces at low temperature will be valuable for comparison with our UPS results. These studies will provide a clearer understanding of the adsorption selectivity of these rare earth oxide surfaces to C2Hz and CzH4 and of the possible correlation between adsorption selectivity and hydrogenation activity. V. Summary and ConclusionsThe adsorption of C2H2 and C2H4 has been studied on both the metallic Gd(0001) surface6 and on the oxidized surface of Gd(0001). Adsorption of both species is dissociative on the metallic surface at 165 K, and there is no detectable adsorption selectivity for these species on the metallic surface. In contrast, the Gd surface after oxidation preferentially adsorbs acetylene over ethylene at a substrate temperature of 165 K. The adsorption probability for acetylene under these conditions is estimated as 0.02 by using measurements of the carbon Auger signal versus exposure. The adsorption probability for ethylene on the oxidized Gd surface at 165 K is, at the very least, a factor of 3 lower and is probably lower by as much as a factor of 100. On the basis of the available UPS data, it is suggested that acetylene adsorbs molecularly on the oxidized surface at low temperature. The molecularly adsorbed CzH2 decomposes below 350 K, leaving carbon on the oxidized Gd surface. The enhanced selectivity of the oxidized Gd surface toward acetylene over ethylene adsorption is unique. This work suggests that studies of the hydrogenation of C2H2 and C2H4 on gadolinium oxide would be useful to probe the possible extension of the selectivity for adsorption into selectivity for hydrogenation.Two new types of highly soluble n...

Single-layer light emitting diodes (LEDs) were fabricated using poly[bis(p-butylphenyl)silane] as the emissive layer. An efficient and stable electroluminescence with a maximum at 407 nm was observed at room temperature under a forward electric field greater than 6×105 V/cm. The coincidence of electroluminescence with photoluminescence suggests the origin of the electroluminescence in an excited silicon chain segment. The high external quantum efficiency (0.1% photons/electron), narrow emission (full width at half maximum=15 nm), improved operating stability, and good solubility in organic solvents provide the possibility of using polysilanes for ultraviolet LEDs.

No abstract

No abstract