Owing to the high technology maturity of thermally activated delayed fluorescence (TADF) emitter design with a specific molecular shape, extremely high-performance organic light‐emitting diodes (OLEDs) have recently been achieved via...

Ar, N2, O2, and N2-O2 mixture under different O2 components were separately used as the working medium gas of a plasma igniter to study the influence of working-medium-gas type and O2 concentration on emission spectral and temperature characteristics of a direct-current arc plasma igniter. The emission spectra of the plasma jet were also analyzed using the optical emission spectroscopy method, and the influence rule of working medium gas and O2 concentration on electron temperature and vibrational temperature of the plasma jet was calculated and analyzed. The experimental results show that the emission spectra of the plasma jet had significant differences when diverse working gases were used as the working medium of the igniter. With increasing O2 concentration in the working medium gas, the spectral line intensity of oxygen-containing particles in emission spectra of the plasma jet was significantly enhanced, and the spectral intensities of nitrogen-containing particles, NO molecular bands, the second positive system of N2C3∏u−B3∏g, and the first negative system of N2+B2∑u+−X2∑u+ were also enhanced obviously. Both electron and vibrational temperature of the plasma jet increased gradually with increasing O2 concentration in the working medium gas, and first increased and then decreased with increasing axial distance from the plasma jet.

A series of σ–π-conjugated polymers composed of biphenyl and X atom as backbone repeat unit (where X is the group IV-A atom: carbon, silicon, germanium, or tin) grafted with two alkoxy-substituted biphenyls at the X atom as side chains are synthesized and their optoelectronic properties are studied systematically. We choose biphenyl rather than alkyl as the side chain because its frontier molecular orbital distributions are close to those of our previously reported σ–π-conjugated polymer grafted with transport moieties. The present σ–π polymers with various X atoms show significant differences in triplet energy (E T) ranging from 2.58 to 2.83 eV with the sequence Ge > Si > C > Sn and in charge mobilities from 10–9 to 10–7 cm2/(V s) with the sequence Si > Ge > Sn > C, indicating that the properties of the σ–π polymers are largely affected by their X atoms. The Ge- and Sn-based σ–π-conjugated polymers show the highest and lowest E T values, respectively, due to their different levels of π-electron delocalization caused by size effects and (d–p)­π orbital interaction. For their charge transport properties, the Si-based conjugated σ–π polymer gives the highest hole and electron mobilities due to the stronger σ–π conjugation and shorter Si–C bond length between the attached carbon atom in biphenyl and Si. On the contrary, the C-based σ–π-conjugated polymer gives the lowest charge mobilities due to a lack of d orbital in the C atom leading to a poor σ–π conjugation characteristic. These σ–π polymers with different E T levels and charge transport properties show a significant effect on their electroluminescence characteristics. Among them, the Ge-based σ–π-conjugated polymer when used as host shows the best device performance due to its higher E T and reasonable charge mobility. Such findings of different optoelectronic properties of these σ–π-conjugated polymers provide useful guidelines for the selection of backbone for designing σ–π-conjugated polymer host grafted with charge transport moieties.

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