Herein, we report a deep‐red TADF emitter pCNQ–TPA, composed of quinoxaline‐5,8‐dicarbonitrile (pCNQ) acceptor and triphenylamine (TPA) donor. pCNQ–TPA supported its OLED with desired CIE coordinates of (0.69, 0.31) and the record maximum external quantum efficiency of 30.3 %, which is the best red TADF diode with Rec.2020 gamut for UHDTV. It is showed that through tuning pCNQ–TPA doping concentration, intra‐ and inter‐molecular charge transfer are balanced to synchronously improve emission color saturation and TADF radiation, and remedy aggregation‐induced quenching, rendering photoluminescence quantum yield (PLQY) reaching 90 % for deep‐red emission peaked at ≈690 nm. Quasi‐planar structure further endows pCNQ–TPA with an improved horizontal ratio of emitting dipole orientation, which increases light out‐coupling ratio to 0.34 for achieving the state‐of‐the‐art device efficiencies.

The primary concern on high power conservation lead to the development of organic electroluminescent (EL) materials from polycyclic aromatic fluorescence (FL), [3] noble-metal-involved phosphorescence (PH) [4] to donor-acceptor (D-A)-featured thermally activated delayed fluorescence (TADF) molecules. [5] Different to 25% electrogenerated excitons, namely singlet excitons, utilized by FL emitters, both PH and TADF materials can harvest 100% excitons in virtue of mutual singlet-triplet conversion through intersystem crossing (ISC) [6] and reverse ISC (RISC). [7] However, FL molecules characteristic of locally excited (LE) states commonly reveal high chromatic purities, whose FWHM values are less than 50 nm. In contrast, charge-transfer (CT) excitedstate components of PH and TADF molecules markedly broaden their emissions by 50-100 nm.Recently, multi-resonance (MR) featured TADF emitters emerge, because of their potential to overcome the challenge in combining high efficiency and emission color purity. [8] This kind of compound has polycyclic aromatic structures with electron-donating and withdrawing atoms, for example, nitrogen and boron, at ortho-positions to form accordant and amplified resonance effects on electron-cloud distribution. [9] In this case, on the one hand, frontier molecular orbitals (FMOs) of MR molecules are separated to facilitate RISC and achieve TADF characteristics; on the other hand, their fused-ring structures limit vibrational relaxation, leading to unique narrowband emissions with FWHM < 30 nm. [10] To balance optoelectrical properties, MR cores were further substituted with functional groups, [11], for example, cyan, [12] fluorine, [13] carbazole, [14] and diphenylamine, [15] which significantly improved carrier injection and transport, resulting in increased luminance and reduced roll-offs. However, to avert spectral broadening, these functional groups were mostly simple, rigid, and finitely extended, which limit the optimal space of MR materials. [16] Nonetheless, it is noticed that most MR diodes should adopt extremely low doping concentrations (commonly <5%) [17] to avoid bimolecular quenching processes, for example, triplet-triplet annihilation (TTA) and triplet-polaron quenching Emerging multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters can combine 100% exciton harvesting and high color purity for their organic light-emitting diodes (OLED). However, the highly planar configurations of MR molecules lead to intermolecular-interactioninduced quenching. A feasible way is integrating host segments into MR molecules, namely a "self-host" strategy, but without involving additional charge transfer and/or vibrational components to excited states. Herein, an ambipolar self-host featured MR emitter, tCBNDADPO, is demonstrated, whose ambipolar host segment (DADPO) significantly and comprehensively improves the TADF properties, especially greatly accelerated singlet radiative rate constant of 2.11 × 10 8 s −1 and exponentially reduced nonradiative rate constants. C...

Organic room temperature phosphorescence (RTP) attracts extensive attentions, but still faces the challenge of achieving both high RTP efficiencies (ηRTP) and long lifetimes (τRTP), due to the intrinsic contradiction between triplet radiation and stabilization. In this work, we developed three carbazole‐triphenylphosphine hybrids named xCzTPP, in which phosphine groups provide nonbonding electrons and steric hindrance to modulate intermolecular p‐π and π‐π interactions. With the rational orientations and spatial positions of functional groups, para‐substituted pCzTPP achieves high ηRTP over 10 % and more than twofold increased τRTP (>600 ms), compared to ortho‐ and meta‐ isomers. Theoretical simulation and photophysical investigation indicate that the strongest intermolecular p‐π and π‐π electronic interplays of pCzTPP harmonize high transition probability of 3pπ state and triplet stability of 3ππ state, reflecting the p‐π and π‐π synergy in RTP process.

A new two-dimensional dysprosium–organic coordination polymer 1-Dy has been synthesized by a hydrothermal method. 1-Dy displays a ferromagnetic interaction between two DyIII ions within the Dy2 dimer and a slow magnetic relaxation with a high effective energy barrier of approximately 160 K under a zero dc field.