A series of new organic emitters was prepared by introducing various donors (Ds) to the meta-position of the boron atom in the central phenyl ring in the acceptor (A) of 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (OBA). Moreover, their thermal, photophysical, electrochemical and electroluminescent (EL) properties were characterized in detail. The photophysical results revealed that these OBA-based molecules adopted a D–A configuration and exhibited efficient thermally activated delayed fluorescence (TADF) properties with a reverse inter-system crossing constant (k_RISC) in the order of 10⁵ s⁻¹. It has been shown that introducing the –Br group to the OBA acceptor could increase k_RISC by 2 to 3 times. Importantly, the deep-blue TADF emitter OBA-O showed a high photoluminescent quantum yield (PLQY) of 0.84, while its blue analog OBA-BrO with the –Br group exhibited an even higher PLQY of 0.92 in the doped film state. Benefitting from their high PLQYs as blue-emitting TADF emitters, the doped organic light-emitting diodes (OLEDs) based on these OBA-based TADF emitters exhibited attractive electroluminescent (EL) performances. The blue-emitting OLEDs with CIE (0.17, 0.17) showed the maximum external quantum efficiency (η_ext) of 17.8%, current efficiency (η_L) of 33.2 cd A⁻¹ and power efficiency (η_P) of 34.2 lm W⁻¹, while that for the bluish-green device were 22.5%, 49.2 cd A⁻¹ and 56.9 lm W⁻¹, respectively. Thus, the great potential of these TADF emitter-based OBA acceptors was clearly demonstrated by their EL data. In addition, these asymmetric OBA-based molecules will enrich the structural diversity of this type of TADF emitter.

The weak spin–orbit coupling (SOC) in metal-free organic molecules poses a challenge in achieving phosphorescence emission. To attain pure phosphorescence in RTP organic emitters, a promising molecular design concept has been proposed. This involves incorporating n → π* transitions and leveraging the heavy atomic effect within the spin–orbit charge transfer-induced intersystem crossing (SOCT-ISC) mechanism of bipolar molecules. Following this design concept, two bipolar metal-free organic molecules (PhSeB and PhSeDB) with donor–acceptor (D–A) and acceptor–donor–acceptor (A–D–A) configurations have been synthesized. When the molecular configuration changes from D–A to A–D–A, PhSeDB exhibits stronger electron coupling and n → π* transitions, which can further enhance the spin–orbit coupling (SOC) together with the heave atom effect from the selenium atom. By the advanced synergism among enhanced n → π* transitions, heavy atom effect and magnified electron coupling to efficiently promote phosphorescence emission, PhSeDB can achieve pure RTP emission in both the solution and doped solid film. Thanks to the higher spin–orbit coupling matrix elements (SOCMEs) for T₁ ↔ S₀, PhSeDB attains the highest phosphorescence quantum yield (ca. 0.78) among all the RTP organic emitters reported. Consequently, the purely organic phosphorescent light-emitting diodes (POPLEDs) based on PhSeDB achieve the highest external quantum efficiencies of 18.2% and luminance of 3000 cd m⁻². These encouraging results underscore the significant potential of this innovative molecular design concept for highly efficient POPLEDs.

Aggregation-induced emission (AIE) has been a vitally important research topic on luminescent materials. AIE-active emitters are usually developed based on the mechanisms of restriction of intramolecular rotation (RIR) or restriction of intramolecular vibration (RIV). Herein, we report a simple phosphorescent Pt(II) complex DPA-Pt that shows impressive AIE behavior mainly because of a new mechanism. In THF/H₂O mixture solutions with the water fraction (f_w) increasing from 0 to 60%, DPA-Pt shows rather weak phosphorescence with the intensities slowly increasing and the emission profiles remaining almost unchanged. Once the f_w reached 70–90%, the emissions are greatly enhanced with new peaks appearing and shifting to longer wavelengths. The emission of the vacuum-deposited DPA-Pt neat film is further red-shifted to the deep-red/near-infrared (NIR) region with the photoluminescence quantum yield (PLQY) markedly increased to 0.33. The experimental and theoretical results indicate that the significant enhancement and red-shift of emissions from in dilute solution to aggregation are mainly triggered by the radiative-transition-switch (RTS) from the intra-ligand charge transfer (ILCT) to the metal–metal-to-ligand charge transfer (MMLCT), indicating that RTS is a new mechanism behind this AIE phenomenon. The non-doped OLED based on DPA-Pt exhibits deep-red/NIR emission with a peak external quantum efficiency of 9.8%, which is not only higher than that of the 6 wt% doped device based on DPA-Pt, but also much higher than those reported for the state-of-the-art non-doped deep-red/NIR OLEDs based on other AIE-active emitters.