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Efficient ultraviolet (UV) electroluminescent materials remain a great challenge, since short peak wavelength <400 nm and narrow full width at half maximum (FWHM) <50 nm are simultaneously required. In this sense, multi‐resonance (MR) thermally activated delayed fluorescence (TADF) emitters featuring narrow‐band emissions hold the promise for UV applications. Herein, a novel MR‐TADF skeleton featuring carbazole‐phosphine oxide (P=O) fused aromatics is developed to construct the first two UV MR emitters named CzP2PO and tBCzP2PO. In addition to synergistic resonance effects of P=O and N atom, sp3‐hybrid P atom renders the curved polycyclic planes of CzP2PO and tBCzP2PO, giving rise to their narrowband UV emissions with peak wavelengths <390 nm and FWHM<35 nm. Besides configuration quasi‐planarization for radiation enhancement and quenching suppression, P=O moiety further enhances singlet‐triplet coupling to facilitate reverse intersystem crossing, resulting in the state‐of‐the‐art photoluminescence quantum yield of 62 % in tBCzP2PO doped films. As consequence, tBCzP2PO endowed its UV organic light‐emitting diodes with the peak at 382 nm and FWHM of 32 nm, and especially the record‐high external quantum efficiency (EQE) of 15.1 % among all kinds of UV devices. Our results demonstrate great potential of P=O based MR emitters in practical applications including optoelectronics, biology and medicine science. [ABSTRACT FROM AUTHOR]

[Display omitted] • "Extra conjugation" method is developed for NIR TADF OLEDs with high radiance. • Intramolecular hydrogen bonds extend molecular conjugation for accurate modulation. • A high radiance of 95,894 m W Sr−1 m−2 with 744 nm peaked EL emission is realized. • Force and medicine induced SpO 2 variations are detected by 740 nm NIR TADF OLED. Real-time in-home monitoring oxygen saturation (SpO 2) is of great significance for early diagnosis and treatment of severe COVID-19, however, which should be based on multi-wavelength technology and complicated equipment. Herein, as a proof of concept, 740 nm is chosen as singlet light source for single-wavelength SpO 2 detection, since absorbance differences between oxyhemoglobin (HbO 2) and other interferences are the most rational. To controllably optimize excited-state characteristics of a near-infrared (NIR) thermally activated delayed fluorescence (TADF) emitters, an "extra conjugation" method is demonstrated by C NQP-TPA , whose 2,3-dicyanoquinoxaline phenanthroline (CNQP) acceptor forms strong intramolecular hydrogen bonds with two phenyls of triphenylamine (TPA) donors, which not only reduce excited-state relaxation-induced energy lose, but also provide more space for accurate modulation of intermolecular charge transfer (CT) interactions. As consequence, at the suitable doping concentration, CNQP-TPA endowed its device with a high radiance reaching ∼105 mW Sr−1 m−2 and desired electroluminescence peak at 744 nm. This device is further used as light source to detect SpO 2 variation under single-wavelength mode. These results indicate the potential of NIR TADF materials and devices for in-home SpO 2 monitoring and pre-diagnosis and prevention of severe COVID-19. [ABSTRACT FROM AUTHOR]

Device simplification is of practical significance for organic light emitting diodes (OLEDs), and remains the great challenge for deep‐red emitters. Herein, a deep‐red thermally activated delayed fluorescence molecule (pTPA‐DPPZ) is reported which features a T shaped structure containing two triphenylamine (TPA) donors, one either side of a planar dipyridophenazine (DPPZ) acceptor. The rational spatial arrangement of the functional groups leads to limited but sufficient molecular packing for effective carrier transport. The neat pTPA‐DPPZ film achieves an around 90‐fold improved radiation rate constant of 107 s−1 and the nearly unitary reverse intersystem crossing (RISC) efficiency, as well as accelerated emission decays for quenching suppression. The high radiation and RISC result in a photoluminescence quantum yield of 87 %. The bilayer OLED based on the pTPA‐DPPZ emissive layer achieved the record external quantum efficiencies of 12.3 % for maximum and 10.4 % at 1000 nits, accompanied by the deep‐red electroluminescence with the excellent color purity. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) organic light‐emitting diodes (OLEDs) show great potential in a variety of applications including sensors, night vision, and information security. Despite the superiority of thermally activated delayed fluorescence (TADF) in 100 % exciton harvesting, the development of NIR TADF OLEDs is still a great challenge, especially in terms of solution‐processing technology. In this work, a multicyano acceptor of 2‐dicyanomethylene‐3‐cyano‐4,5,5‐trimethyl‐2,5‐dihydrofurance (TCF) with strong electron‐withdrawing ability was employed to construct solution‐processible NIR emitters, CzTCF and tBCzTCF, with the feature of donor–π–acceptor (D–π–A) structure. The significantly enhanced intermolecular charge transfer effects not only render the deep‐red and NIR emissions of CzTCF and tBCzTCF films, respectively, but also lead to their typical TADF characteristics. Consequently, the nondoped solution‐processed NIR OLED based on tBCzTCF was successfully demonstrated with the peak wavelength of 715 nm, which paves the way for developing NIR emitters without polycyclic aromatic cores and heavy‐metal ions. A multicyano‐substituted acceptor and styryl π‐conjugate linker were both optimized to realize efficient NIR thermally activated delayed fluorescence (TADF) emitters (CzTCF and tBCzTCF) with simple D–π–A structure. The three linearly distributed cyano groups in TCF and the longer conjugation in the styryl π‐linker effectively regulated the D–A interactions and the frontier molecular orbital distributions (see scheme). [ABSTRACT FROM AUTHOR]

[Display omitted] • "Asymmetric D-A-wA" strategy is demonstrated for high-efficiency red TADF emitters. • Diphenylphosphine oxide as the second acceptor markedly improves TADF properties. • Strong red emission peaked at 645 nm with a high PLQY of 94.7 % is realized. • The maxima of 19360 cd m−2 for luminance and 11.4 % for EQE at 632 nm are achieved. A feasible strategy of asymmetric donor–acceptor-second acceptor (D-A-A) structure is proposed for improving the photoluminecense (PL) and electroluminescence (EL) performance of red thermally activated delayed fluorescence (TADF) emitters. As a concept, four newly TADF emitters are designed and synthesized, D-A-A structure o TPAPO-DTPZ and p TPAPO-DTPZ and D-A-D type o DTPA-DTPZ and p DTPA-DTPZ, by using triphenylamine (TPA), dithieno[2,3- a :3′,2′- c ]phenazine (DTPZ) and diphenylphosphine oxide (DPPO) groups as the donor, acceptor and second acceptor, respectively. It is demonstrated that abound intra- and inter-molecular C H···O hydrogen bonds are forming between TPA donor and DPPO acceptor for the asymmetric compounds, which effectively promote the intra- and inter-molecular charge transfer. Moreover, the steric hindrance of DPPO group availably suppresses the concentration quenching. As a consequence, the asymmetric D-A-A structured o TPAPO-DTPZ and p TPAPO-DTPZ exhibit relatively higher PL quantum yields and lower nonradiation rates, and thus better EL performance. In particular, device based on p TPAPO-DTPZ achieves the maximum luminance of 19360 cd m−2 and external quantum efficiency of 11.4 % at 632 nm, which are 2.3 and 1.5 times the values of p DTPA-DTPZ based device. [ABSTRACT FROM AUTHOR]

[Display omitted] • Near-infrared TADF emission from phenanthroline based molecule is demonstrated. • NIR emission and radiation efficiency are balanced in CNPP-TPA. • Strong NIR emission peaked at 701 nm with PLQY of 96.5% is realized. • A maximum EQE (8.69%) of vacuum-evaporated device peaked at 684 nm is achieved. • A maximum EQE (2.02%) of spin-coated device peaked at 700 nm is achieved. Efficient thermally activated delayed fluorescence (TADF) emitters are of practical significance for realizing high-performance organic light emitting diodes (OLEDs), which remains the great challenge for near-infrared (NIR) emitters because of their narrow bandgap worsened non-radiative transition. Herein, a NIR TADF molecule (CNPP-TPA) is reported, composed of 2,3-dicyanopyrazino phenanthroline (CNPP) as acceptor and triphenylamine as donor. The strong electron-withdrawing effect of CNPP and intramolecular hydrogen bond endow CNPP-TPA with efficient NIR photoluminescence emission peaked at 701 nm with a high photoluminescence quantum yield of 96.5%, owing to rapid singlet radiation and effective reverse intersystem crossing. Vacuum -evaporated and spin-coated organic light-emitting diodes exhibit the NIR emissions respectively peaked at 684 nm and 700 nm, corresponding to Commission International de L'Eclairage (CIE) coordinates of (0.68, 0.31) and (0.69, 0.30), respectively. Significantly, these two devices achieved the state-of-the-art external quantum efficiencies of 8.69% and 2.02%. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) thermally activated delayed fluorescence (TADF) materials have great potential for applications in many fields. However, it is more challenging for such kinds of materials to achieve efficient NIR emission in comparison to visible light. Herein, as a proof of concept, three acceptors are regularly aligned to optimize intramolecular charge transfer (ICT) interactions in donor‐π‐acceptor molecules to improve bathochromic shift and TADF performance, which successfully supports the application in NIR OLEDs. More information can be found in the Full Paper by C. Han, H. Xu, et al. on page 1010. [ABSTRACT FROM AUTHOR]