Ultraviolet (UV) organic emitters that can open up applications for future organic light-emitting diodes (OLEDs) are of great value but rarely developed. Here, we report a highquality UV emitter with hybridized local and charge-transfer (HLCT) excited state and its application in UV OLEDs. The UV emitter, 2BuCz-CNCz, shows the features of low-lying locally excited (LE) emissive state and high-lying reverse intersystem crossing (hRISC) process, which helps to balance the color purity and exciton utilization of UV OLED. Consequently, the OLED based on 2BuCz-CNCz exhibits not only a desired narrowband UV electroluminescent (EL) at 396 nm with satisfactory color purity (CIE x, y = 0.161, 0.031), but also a record-high maximum external quantum efficiency (EQE) of 10.79 % with small efficiency roll-off. The state-ofthe-art device performance can inspire the design of UV emitters, and pave a way for the further development of highperformance UV OLEDs.

Hot exciton luminogens capable of harvesting nonemissive triplet excitons via reverse intersystem crossing from high-order triplet (hRISC) to singlet have great potential in high-efficiency fluorescent organic light-emitting diodes (OLEDs). Although spin–orbit coupling (SOC) is regarded as a key factor affecting the RISC process, its effects on hot exciton materials are poorly understood. Herein, we design and synthesize two blue-emitting hot exciton luminogens, PABP and PAIDO, to study this issue by modulating the excited-state properties. Theoretical and experimental research contributions demonstrate that a stronger SOC between energetically close S1 (π–π*) and T n (T3, n−π*) of PAIDO gives rise to faster and more efficient hRISC in comparison to that of PABP, leading to a higher external quantum efficiency and a higher exciton utilization efficiency. Crucially, the experimentally measured hRISC rate (k hRISC) of hot exciton materials is on the order of 107 s–1, which is much faster than that of the thermally activated delayed fluorescence materials.

Aggregation‐induced emission (AIE) materials are attractive for achieving highly efficient nondoped organic light‐emitting diodes (OLEDs) owing to their strong luminescence in the solid state. However, the electroluminescence efficiency of most AIE‐based OLEDs remains low owing to the waste of triplet excitons. Here, using theoretical calculations, photophysical dynamics, and magnetoluminescence measurements, the spin conversion process is demonstrated between the high‐lying triplet state (Tn) and the lowest excited singlet state (S1) in AIE materials. Moreover, the relative positions of Tn (n < 4) and S1 are shown to have a significant impact on the spin‐conversion efficiency, thus influencing the harvesting of triplet excitons and the device efficiency. Finally, by selecting an upconversion material with an appropriate energy level for further utilizing the triplet excitons, a deep‐blue fluorescent OLED with CIE coordinates of (0.15, 0.08), a maximum external quantum efficiency of 10.2%, low efficiency roll‐off, and a high brightness of 16817 cd m−2 is developed. This is one of the most efficient deep‐blue OLEDs based on AIE materials reported so far. These findings also provide new insights into the design of more efficient AIE molecules and corresponding OLEDs by managing high‐lying triplet excitons.

Aggregation‐induced emission (AIE) materials are highly attractive because of their excellent properties of high efficiency emission in nondoped organic light‐emitting diodes (OLEDs). Therefore, a deep understanding of the working mechanisms, further improving the electroluminescence (EL) efficiency of the resulting AIE‐based OLEDs, is necessary. Herein, the conversion process from higher energy triplet state (T2) to the lowest singlet state (SS1) is found in OLEDs based on a blue AIE material, 4′‐(4‐(diphenylamino)phenyl)‐5′‐phenyl‐[1,1′:2′,1′′‐terphenyl]‐4‐carbonitrile (TPB‐AC), obviously relating to the device efficiency, by magneto‐EL (MEL) measurements. A special line shape with rise at low field and reduction at high field is observed. The phenomenon is further clarified by theoretical calculations, temperature‐dependent MELs, and transient photoluminescence emission properties. On the basis of the T2‐S1 conversion process, the EL performances of the blue OLEDs based on TPB‐AC are further enhanced by introducing a phosphorescence doping emitter in the emitting layer, which effectively regulates the excitons on TPB‐AC molecules. The maximum external quantum efficiency (EQE) reaches 7.93% and the EQE keeps 7.57% at the luminance of 1000 cd m−2. This work establishes a physical insight for designing high‐performance AIE materials and devices in the future.

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.