A novel, efficient, deep-blue fluorescent emitter mPAC, with a meta-connected donor–acceptor structure containing phenanthroimidazole (PPI) as the donor and phenylcarbazole-substituted anthracene (An-CzP) as the acceptor, was designed and synthesized. The meta-linkage provided a highly twisted molecular conformation, which efficiently interrupts the intramolecular π-conjugation, resulting in a deep-blue emission. The optimized nondoped device based on mPAC displayed a deep-blue emission with a narrow full width at half-maximum of 56 nm and Commission Internationale de L’Eclairage coordinates of (0.16, 0.09). The maximum external quantum efficiency (EQEmax) is 6.76%, corresponding to a high exciton utilization efficiency (EUE) of 59.3–88.9%. Experimental results and theoretical analysis indicated that the high EUE is mainly ascribed to the reverse intersystem crossing (RISC) from T2 to S1, a “hot exciton” path in which the large T2–T1 energy gap (1.45 eV) and small T2–S1 energy difference (0.18 eV, T2 > S1) hamper the internal crossing from T2 to T1 and facilitate the RISC process. For the hot exciton path, the T2 state can be feasibly arranged to a high energy level, forming a thermal equilibrium with S1, even slightly higher than the deep-blue S1 to realize an exergonic RISC process, which is usually difficult for the thermally activated delayed fluorescence emitters.

In electrochemistry, the carbazole is generally coupled to dimer but not to polymer. This work has reported that organic electropolymerization (OEP) of 4,4′,4″-tri­(N-carbazolyl)­triphenylamine (TCTA) would form a high cross-linked carbazole polymer by its high activity/reversibility and a synchronous viscosity control. It has significantly improved the OEP film quality of both hole-transporting and electroluminescent layers in organic light-emitting diodes. As a result, the conductivity and power efficiency of the organic light-emitting diodes with TCTA are eight and four times of that without TCTA. A prototype display device with a 1.7 in. monochrome passive matrix of 58 ppi under the driving chip is successfully fabricated with accurate pixel size and uniform electroluminescence, which shows a great potential of OEP in the electroluminescent application.

The quality of high‐resolution luminescent films is key for high‐definition and near‐eye displays, but is limited by the apparent boundary effects at sub‐micrometer scales, such as boundary quenching in inorganic light‐emitting diodes and the coffee ring effect in inkjet printing. This study demonstrates that the electroplating of electrified electrode microarrays is not limited by boundary effects, enabling the deposition of luminescent dyes as high‐quality films with uniform and smooth morphologies as well as strong electroluminescence. As radial diffusion is the key to boundary effect in electroplating technology, small pixels tend to weaken the boundary effects and ease the overlap of diffusion layers. When the pixel size is lower than the critical value, the boundary effects can be eliminated. The smallest pixel width attempted is 3 µm, and prototype devices of monochrome and red‐green‐blue‐colored pixel arrays are successfully fabricated on glass and flexible backplanes without bad pixels and lines, indicating the high potential of the electroplating technique to achieve high‐resolution and immersive virtual reality for fine displays.

No abstract