Resonant inelastic soft-x-ray scattering spectra at the N1s and C1s edges of poly(pyridine-2,5-diyl)

Resonant inelastic scattering measurements of poly(pyridine-2,5-diyl) have been performed at the N1s and C1s edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the p electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of s symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer.Comment: 6 pages, 3 figures, http://www.sciencedirect.com/science/article/pii/S036820489800354

The electronic structure of poly(pyridine-2,5-diyl) investigated by soft x-ray absorption and emission spectroscopies

The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and nonresonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the {\pi} electron bands in line with symmetry selection and momentum conservation rules. The effect is most vizual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of {\sigma} symmetry and are less frequency dependent.Comment: 11 pages, 7 figures, 1 table, http://www.sciencedirect.com/science/article/pii/S030101049800262

Triplet energies of pi-conjugated polymers

Using pulse radiolysis and triplet energy transfer has enabled us to measure the triplet energies in a broad range of different pi -conjugated polymers. In all eases we find that the 1(3)B(u) is Of order 0.6 to 1 eV below the 1 B-1(u), indicative of localized triplet states with strong electron- electron correlation. We also observe that the 1(1)A(g)- 1(3)B(u), gap decreases linearly as the I(1)A(g)-1(1)B(u) gap decreases even though polymers with very different structure have been studied. This surprising result suggests that polymers with singlet gap <1.3 eV will have a triplet ground state

The effect of insulating spacer layers on the electrical properties of polymeric Langmuir-Blodgett film light emitting devices

We report on the use of insulating Langmuir-Blodgett (LB) films to improve the quantum efficiency of light emitting devices based on polymeric LB films. The insertion of arachidic acid layers between a poly-(2-methoxy,5-(2'ethylhexyloxy)-p -phenylenevinylene) (MEH-PPV) film and an aluminium cathode was found to decrease the turn-on voltage for electroluminescence and to double the quantum efficiency. In contrast, depositing the fatty acid layer between the polymer and the indium tin oxide anode produced little change in the device efficiency. Dual-layer structures using MEH-PPV as the light emissive layer and poly-(p -(3-hexyl pyridylene)) as an electron transport layer were also tested. Again, an increase in device efficiency could be obtained by placing arachidic acid LB layers immediately beneath the metallic cathode

Self-Organized Liquid Phase and Co-Crystallization of Rod-Like Polymers Hydrogen-Bonded to Amphiphilic Molecules

Negative Poisson&apos;s ratio (NPR) materials ???which shrink along one axis when compressed along an orthogonal one???are currently composed of reentrant cells with dimensions greater than 1 mm. The fabrication of NPR materials from various materials and in various cell geometries with dimensions in the micrometer range, for example the epoxy NPR material shown in the Figure, is described

Triplet state dynamics in Poly(2,5-pyridine diyl)

Pulse radiolysis was used to determine the triplet state energy (2.3 eV) of Poly(2,5-pyridine diyl) (PPY) film which was found to be coincident with the emission energy. Detailed time-resolved photoluminescence (PL) and pump-probe measurements have been applied to study the photoexcited state relaxation dynamics. In films, a very large spectral red-shift (~0.35 eV) for the PL occurred within the first 100 ps whereas no spectral red-shift was observed for the PPY in solution. This result shows clear evidence for the evolution of short-lived singlet emission (S1-->S0) at ~450 nm to long-lived triplet emission (T1-->S0) at ~520 nm for the PPY thin film. Streak camera measurement indicates the long live component has a decay time constant of several ns. The picosecond photo-induced triplet state absorption (T1-->T2 transition) peaks at ~600 nm as measured by pump-probe which is consistent with both the radiolysis and cw photo-induced absorption measurements. A triplet lifetime of ~6 ns is measured which is again consistent with the streak camera measurement. These results lead us to believe that the long live component of the emission from PPY film is in fact phosphorescence. Furthermore, there is evidence that oxygen plays a very important role in the fast triplet radiative lifetime in PPY films.http://www.sciencedirect.com/science/article/B6TY7-41XMFCG-6/1/e8eb864b0a7e6582ef22a9cc934d62d