Light-emitting diodes are fabricated from regioregular and non-regioregular poly( 3-hexylthiophenes). The regioregular polymer has a higher head-to-tail (HT) ratio than non-regioregular polymer. It is shown that the electroluminescent device containing high HT ratio polymer perform significantly better than polymers with a low HT ratio. Photoluminescence data of both polymers are also reported.

ragonal transition at the equilibrium state occurs at about 550 °C. Here we have shown that under CH4 atmosphere the onset temperature is lowered by at least 150 °C. This result is consistent with the assumption that the out-diffusion rate of oxygen in the YBaCuO compound is limited by a surface barrier of 1.7 eV, which is involved in the surface diffusion of Ospecies and the further formation and desorption of 02.13 In the presence of methane this surface barrier is lowered as a result of the strong chemical interaction between Osurface species and CH4 molecules of the gas phase.New experiments are being conducted in our laboratory in order to determine the catalytic properties of the YBaCuO superconductor in the selective oxidation of methane to C2 hydrocarbons in the presence of free molecular oxygen.

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The lifetime of the molecular triplet state formed by recombination of the radical ion pair in quinonedepleted bacterial photosynthetic reaction centers is found to depend on applied magnetic field strength. It is suggested that this magnetic field effect results from thermally activated repopulation of the same radical ion pair that generates the triplet. Consistent with this hypothesis, the magnetic field effect on the triplet lifetime disappears at low temperature where the triplet state decays exclusively by ordinary intersystem crossing. This activated pathway for the decay of the triplet state can explain the strong temperature dependence of the triplet decay rate. A detailed theoretical treatment of the problem within a set of physically reasonable assumptions relates the observed temperature dependence of the triplet decay rate to the energy gap between the radical ion pair intermediate and the triplet state. This energy gap is estimated to be about 950 cm 1 (0.12 eV). Combined with an estimate of the energy of the donor excited state, we obtain an energy gap between the excited sinFlet state of the donor and the radical ion pair of 2,250 cm-(0.28 eV).