Three blue‐light emitting dipyrenylbenzene derivatives, 1‐(4‐(1‐pyrenyl)phenyl)pyrene (PPP), 1‐(2,5‐dimethoxy‐4‐(1‐pyrenyl)phenyl)pyrene (DOPPP), and 1‐(2,5‐dimethyl‐4‐(1‐pyrenyl)phenyl)pyrene (DMPPP), have been prepared by the Suzuki coupling reaction of aryl dibromides with pyreneboronic acid in high yields. These compounds exhibit high glass‐transition temperatures of 97–137 °C and good film‐forming ability. As revealed from single‐crystal X‐ray analysis, these dipyrenylbenzenes adopt a twisted conformation with inter‐ring torsion angles of 44.5°–63.2° in the solid state. The twisted structure is responsible for the low degree of aggregation in the thin films that leads to fluorescence emission of the neat films at 446–463 nm, which is shorter than that of the typical pyrene excimer emission. The low degree of aggregation is also conducive for the observed high fluorescence quantum yields of 63–75%. In organic light‐emitting diode (OLED) applications, these dipyrenylbenzenes can be used as either the charge transporter or host emitter. The non‐doped blue OLEDs that employ these compounds as the emissive layer can achieve a very high external quantum efficiency (ηext) of 4.3–5.2%. In particular, the most efficient DMPPP‐based device can reach a maximum ηext of 5.2% and a very high luminescence of 40 400 cd m–2 in the deep‐blue region with Commission Internationale d'Énclairage (CIE) coordinates of (0.15, 0.11).

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In this study, the electrical properties of Pt contacts on p-type GaN (p-GaN) activated in air were investigated. From the observed photoluminescence result, it is suggested that the hydrogenated Ga vacancies (i.e., VGaH2) were formed during the activation process. However, VGaH2 in p-GaN near the surface was transformed into VGa after Pt deposition, because Pt strongly absorbed hydrogen. A large number of VGa at the Pt/p-GaN interface would lead to the pinning of the Fermi level at 0.3 eV above the valence-band edge, as well as the formation of the low barrier at the interface, and the formation of the nonalloyed ohmic contacts due to the occurrence of the tunneling transmission for holes at the interface.

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