With 2-(2,4-difluorophenyl)pyridine (dfppy) as the first cyclometalated ligand and different monoanionic N-heterocyclic carbenes (NHCs) as the second cyclometalated ligands, 16 blue or greenish-blue neutral iridium(III) phosphorescent complexes, (dfppy)2Ir(NHC), were synthesized efficiently. The obtained Ir(III) complexes display typical phosphorescence of 455-485 nm with quantum yields up to 0.73. By modifying the phenyl moiety in the NHCs with electron-withdrawing substituents (e.g., -F or -CF3) or replacing it with N-heteroaromatic rings (pyridine or pyrimidine), the HOMO-LUMO gaps are broadened, and the emissions shift to the more blue region accordingly. Furthermore, to extend the application scope of NHCs as the second cyclometalated ligands, five other Ir(III) complexes from blue to red were synthesized with different first cyclometalated ligands. Finally, the organic light-emitting diodes using one blue emitter exhibit a maximum current efficiency of 37.83 cd A(-1), an external quantum efficiency of 10.3%, and a maximum luminance of 8709 cd m(-2). Our results demonstrate that NHCs as the second cyclometalated ligands are good candidates for the achievement of efficient phosphorescent Ir(III) complexes and corresponding devices.
In this paper, we report the influence of oxygen and hydrogen additives in the metal melt on the growth process, morphology, and defect-and-impurity structure of large single-crystal diamonds.
The chemical composition can directly tune the transport properties of Cu2Se liquid-like materials, including the carrier concentration, carrier mobility and superionic feature.
High-pressure technique is an effective route to synthesize thermoelectric materials and tune transport properties simultaneously. In this work, S-doped copper–selenium compounds [Formula: see text], [Formula: see text] were successfully synthesized by high-pressure and high-temperature (HPHT) technology in just 30 min. [Formula: see text] samples show layered morphology composed of abundant pores and lattice defects. The appropriate S introduction ([Formula: see text] and 0.03) can effectively enhance Seebeck coefficient and reduce the thermal conductivity of [Formula: see text]. Compared with the pure [Formula: see text] sample, [Formula: see text] exhibits a 30% lower thermal conductivity, but the decline of power factor by the distinctly increased electrical resistivity at high temperature results in a smaller zT at temperature [Formula: see text] K. The variations of thermoelectric properties are resulted from the competitive effects between S-doping and actual composition change (Cu:S). It indicates that S-doping is not so effective in improving the zT value of [Formula: see text] materials by high-pressure synthesis.
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