Planar and Rigid Pyrazine Based TADF Emitter for Deep Blue Bright Organic Light Emitting Diodes

<p>Two blue thermally activated delayed fluorescence (TADF) emitters bearing di-<i>tert</i>-butyl carbazoles as the electron donor groups and pyrazine (<b>DTCz-Pz</b>) or dipyrazine (<b>DTCz-Pz</b>) as the electron acceptor are presented. The DFT calculations predict <b>DTCz-Pz</b> and <b>DTCz-DPz</b> to possess high S₁ energies (3.19 eV and 3.08 eV, respectively), and relatively large E_ST values (0.52 eV and 0.56 eV, respectively). The closely layered intermediate triplet states between S₁ and T₁, predicted by DFT calculations, are expected to facilitate the reverse intersystem crossing (RISC) and improve spin-vibronic coupling efficiency between the excited states even the relatively larger ΔE_STs. The ΔE_STs for <b>DTCz-Pz</b> and <b>DTCz-DPz</b> are 0.27 eV and 0.38 eV, and both molecules show high photoluminescence quantum yields (65%, and 70%, respectively) and the decay lifetimes show temperature dependence in a PPT host, which is consistent that both molecules are TADF emitters in PPT. The OLEDs based on <b>DTCz-Pz</b> exhibit deep blue emission with λ_EL of 460 nm and CIE of (0.15, 0.16). The maximum external quantum efficiency (EQE_max) reaches 11.6%, with a maximum luminance (L_max) of up to 6892 cd m^-2, while the device based on <b>DTCz-DPz</b> exhibits sky blue emission with λ_EL of 484 nm and CIE of (0.15, 0.30), an EQE_max of 7.2%, and L_max of 8802 cd m^-2.</p>

Planar and Rigid Pyrazine Based TADF Emitter for Deep Blue Bright Organic Light Emitting Diodes

<p>Two blue thermally activated delayed fluorescence (TADF) emitters bearing di-<i>tert</i>-butyl carbazoles as the electron donor groups and pyrazine (<b>DTCz-Pz</b>) or dipyrazine (<b>DTCz-Pz</b>) as the electron acceptor are presented. The DFT calculations predict <b>DTCz-Pz</b> and <b>DTCz-DPz</b> to possess high S₁ energies (3.19 eV and 3.08 eV, respectively), and relatively large E_ST values (0.52 eV and 0.56 eV, respectively). The closely layered intermediate triplet states between S₁ and T₁, predicted by DFT calculations, are expected to facilitate the reverse intersystem crossing (RISC) and improve spin-vibronic coupling efficiency between the excited states even the relatively larger ΔE_STs. The ΔE_STs for <b>DTCz-Pz</b> and <b>DTCz-DPz</b> are 0.27 eV and 0.38 eV, and both molecules show high photoluminescence quantum yields (65%, and 70%, respectively) and the decay lifetimes show temperature dependence in a PPT host, which is consistent that both molecules are TADF emitters in PPT. The OLEDs based on <b>DTCz-Pz</b> exhibit deep blue emission with λ_EL of 460 nm and CIE of (0.15, 0.16). The maximum external quantum efficiency (EQE_max) reaches 11.6%, with a maximum luminance (L_max) of up to 6892 cd m^-2, while the device based on <b>DTCz-DPz</b> exhibits sky blue emission with λ_EL of 484 nm and CIE of (0.15, 0.30), an EQE_max of 7.2%, and L_max of 8802 cd m^-2.</p>

Film Growth Mechanism of Photo-Chemical Vapor Deposition

The photo-chemical vapor deposition (CVD) of SiO2 and SiN2 were investigated using 185 nm light of a low pressure mercury lamp. The film thickness deposited on the substrate was the function of the distance from the substrate to the light source and its relation was investigated by changing the reaction pressure. From these investigations, the space migration length of the active species was estimated, which was, at the processing pressure of 400 Pa, about 10–20 mm. This migration length was confirmed by a model calculation. The step coverage of the film was investigated by the use of a two-dimensional capillary cavity. It was shown that the thickness decayed exponentially with the depth in the cavity. The decay constant did not show temperature dependence. From this result, the surface migration of the active species produced by photo-CVD was reported. To confirm this migration we presented a substrate- size effect of photo-CVD, which became obvious when the substrate size became smaller than the space migration length of the active species. From these results, the film growth mechanism of photo-CVD was discussed.

Differential thermal analyses of solid-solid transitions in AgNO3 under hydrostatic pressures to 0.7 Gpa

Differential thermal analyses have located the transitions between low-temperature I and high-temperature II phases in AgNO3 powder and single crystals under hydrostatic pressures </~0.7 GPa, with heating/cooling rates in the range 0.1-1.5 K s-1. Isobaric transition temperatures plot linearly against heating/cooling rates and, extrapolated to zero rate, show hystereses between I → II and II → I transition temperatures which are comparable with the 'regions of indifference' of Bridgman's isothermal experiments. The present results suggest an initial slope of -0.090 μK Pa-1 and zero initial curvature for the I-II phase boundary. Greater hystereses are observed for the I-II transitions near intersection with the II-II' λ transition at </~0.7 GPa. An improved, quantitative description is achieved for the Kennedy-Schultz data on the linear growth rates of II,II? → I at 0.1 MPa. For II' (with ordered NO3- ions) → I the growth rates show temperature dependence markedly different than growth rates for II(with disordered NO3-) → 1 and I → II.