Exploring Robust Delayed Fluorescence Materials via Structural Rigidification for Realizing Organic Light-Emitting Diodes with High Efficiencies and Small Roll-Offs.

Thermally activated delayed fluorescence (TADF) materials have been widely studied for the fabrication of high-performance organic light-emitting diodes (OLEDs), but the serious efficiency roll-offs still remain unsolved in most cases. Herein, it is wish to report a series of robust green TADF compounds containing rigid xanthenone acceptor and acridine-based spiro donors. The enhancement in molecular rigidity not only endows the compounds with improved thermal stability but also results in reduced geometric vibrations and thus lowered reorganization energies. These compounds exhibit distinct merits of high thermal stabilities, excellent photoluminescence quantum efficiencies (96%-97%), large horizontal dipole orientation ratios (87.4%-92.1%) and fast TADF rates (1.4-1.5 × 106 s-1 ). The OLEDs using them as emitters furnish superb electroluminescence performances with outstanding external quantum efficiencies (ηext s) of up to 37.4% and very small efficiency roll-offs. Moreover, highly efficient hyperfluorescence OLEDs are obtained by using them as sensitizers for the green mutilresonance TADF emitter BN2, delivering excellent ηext s of up to 34.2% and improved color purity. These results disclose the high potential of these TADF compounds as emitters and sensitizers for OLEDs.

Simultaneously Realizing High Efficiency and High Color Rendering Index for Hybrid White Organic Light-Emitting Diodes by Ultra-Thin Design of Delayed Fluorescence Sensitized Phosphorescent Layers.

In consideration of energy economization and light quality, concurrently attaining high external quantum efficiency (ηext ) and high color rendering index (CRI) is of high significance for the commercialization of hybrid white organic light-emitting diodes (WOLEDs) but is challenging. Herein, a blue luminescent molecule (2PCz-XT) consisting of a xanthone acceptor and two 3,6-diphenylcarbazole donors is prepared, which exhibits strong delayed fluorescence, short delayed fluorescence lifetime, and excellent electroluminescence property, and can sensitize green, orange, and red phosphorescent emitters efficiently. By employing 2PCz-XT as sensitizer and phosphorescent emitters as dopants, efficient two-color and three-color WOLED architectures with ultra-thin phosphorescent emitting layers (EMLs) are proposed and constructed. By incorporating a thin interlayer to modulate exciton recombination zone and reduce exciton loss, high-performance three-color hybrid WOLEDs are finally achieved, providing a high ηext of 26.8% and a high CRI value 83 simultaneously. Further configuration optimization realizes a long device operational lifetime. These WOLEDs with ultra-thin phosphorescent EMLs are among the state-of-the-art hybrid WOLEDs in the literature, demonstrating the success and applicability of the proposed device design for developing robust hybrid WOLEDs with superb efficiency and color quality.

Interfacial Modulation of Ti3C2Tx MXene by Cellulose Nanofibrils to Construct Hybrid Fibers with High Volumetric Specific Capacitance.

The intrinsic poor rheological properties of MXene inks result in the MXene nanosheets in dried MXene microfibers prone to self-stacking, which is not conducive to ion transport and diffusion, thus affecting the electrochemical performance of fiber-based supercapacitors. Herein, robust cellulose nanofibrils (CNF)/MXene hybrid fibers with high electrical conductivity (916.0 S cm-1) and narrowly distributed mesopores are developed by wet spinning. The interfacial interaction between CNF and MXene can be enhanced by hydrogen bonding and electrostatic interaction due to their rich surface functional groups. The interfacial modulation of MXene by CNF can not only regulate the rheology of MXene spinning dispersion, but also enhance the mechanical strength. Furthermore, the interlayer distance and self-stacking effect of MXene nanosheets are also regulated. Thus, the ion transport path within the fiber material is optimized and ion transport is accelerated. In H2SO4 electrolyte, a volumetric specific capacitance of up to 1457.0 F cm-3 (1.5 A cm-3) and reversible charge/discharge stability are demonstrated. Intriguingly, the assembled supercapacitors exhibit a high-volume energy density of 30.1 mWh cm-3 at 40.0 mW cm-3. Moreover, the device shows excellent flexibility and cycling stability, maintaining 83% of its initial capacitance after 10 000 charge/discharge cycles. Practical energy supply applications (Power for LED and electronic watch) can be realized.

Boosting Circularly Polarized Luminescence from Alkyl-Locked Axial Chirality Scaffold by Restriction of Molecular Motions.

Boosting the circularly polarized luminescence of small organic molecules has been a stubborn challenge because of weak structure rigidity and dynamic molecular motions. To investigate and eliminate these factors, here, we carried out the structure-property relationship studies on a newly-developed axial chiral scaffold of bidibenzo[b,d]furan. The molecular rigidity was finely tuned by gradually reducing the alkyl-chain length. The environmental factors were considered in solution, crystal, and polymer matrix at different temperatures. As a result, a significant amplification of the dissymmetry factor glum from 10-4 to 10-1 was achieved, corresponding to the situation from (R)-4C in solution to (R)-1C in polymer film at room temperature. A synergistic strategy of increasing the intramolecular rigidity and enhancing the intermolecular interaction to restrict the molecular motions was thus proposed to improve circularly polarized luminescence. The though-out demonstrated relationship will be of great importance for the development of high-performance small organic chiroptical systems in the future.

Creating Efficient Red Thermally Activated Delayed Fluorescence Materials with Cyano-Substituted 11,12-Diphenyldipyrido[3,2-a:2',3'-c]phenazine Acceptors.

Red luminescent materials are essential components for full color display and white lightening based on organic light-emitting diode (OLED) technology, but the extension of emission color towards red or deep red region generally leads to decreased photoluminescence and electroluminescence efficiencies. Herein, we wish to report two new luminescent molecules (2CNDPBPPr-TPA and 4CNDPBPPr-TPA) consisting of cyano-substituted 11,12-diphenyldipyrido[3,2-a:2',3'-c]phenazine acceptors and triphenylamine donors. As the increase of cyano substituents, the emission wavelength is greatly red-shifted and the reverse intersystem crossing process is promoted, resulting in strong red delayed fluorescence. Meanwhile, due to the formation of intramolecular hydrogen bonds, the molecular structures become rigidified and planarized, which brings about large horizontal dipole ratios. As a result, 2CNDPBPPr-TPA and 4CNDPBPPr-TPA can perform as emitters efficiently in OLEDs, furnishing excellent external quantum efficiencies of 28.8 % at 616 nm and 20.2 % at 648 nm, which are significantly improved in comparison with that of the control molecule without cyano substituents. The findings in this work demonstrate that the introduction of cyano substituents to the acceptors of delayed fluorescence molecules could be a facile and effective approach to explore high-efficiency red or deep red delayed fluorescence materials.

Homochiral Tetraphenylethene-Based Metal-Organic Frameworks with Circularly Polarized Luminescence for Enantioselective Recognition.

A pair of water-stable and highly porous homochiral fluorescent silver-organic framework enantiomers, namely, R-Ag-BPA-TPyPE (R-1) and S-Ag-BPA-TPyPE (S-1), had been prepared as enantioselective fluorescence sensors. Combining homochiral 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BPA) with an AIE-based ligand tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPyPE) in complexes R-1 and S-1 made them possess favorable circularly polarized luminescence (CPL) properties, and their CPL spectra were almost mirror images of each other. The luminescence dissymmetry factors (glum) are ±2.2 × 10-3 for R-1 and S-1, and the absolute fluorescence quantum yields (ΦFs) are 32.0% for R-1 and S-1, respectively. Complex R-1 could enantioselectively recognize two enantiomers of amino acids in water or DMF with high Stern-Volmer constants of 236-573 M-1 and enantioselectivity ratios of 1.40-1.78.

Precise molecular engineering for the preparation of pyridinium photosensitizers with efficient ROS generation and photothermal conversion.

Organic photosensitizers (PSs) with aggregation-induced emission properties have great development potential in the integrated application of multi-mode diagnosis and treatment of photodynamic therapy (PDT) and photothermal therapy (PTT). However, preparing high-quality PSs with both optical and biological properties, high reactive oxygen species (ROS) and photothermal conversion ability are undoubtedly a great challenge. In this work, a series of pyridinium AIE PSs modified with benzophenone have been synthesized. A wide wavelength range of fluorescent materials was obtained by changing the conjugation and donor-acceptor strength. TPAPs5 has a significant advantage over similar compounds, and we have also identified the causes of high ROS generation and high photothermal conversion in terms of natural transition orbitals, excited state energy levels, ground-excited state configuration differences and recombination energy. Interestingly, migration of target sites was also found in biological imaging experiments, which also provided ideas for the design of double-targeted fluorescent probes. Therefore, the present work proposed an effective molecular design strategy for synergistic PDT and PTT therapy.

Switchable Dual Circularly Polarized Luminescence in Through-Space Conjugated Chiral Foldamers.

Organic materials with switchable dual circularly polarized luminescence (CPL) are highly desired because they can not only directly radiate tunable circularly polarized light themselves but also induce CPL for guests by providing a chiral environment in self-assembled structures or serving as the hosts for energy transfer systems. However, most organic molecules only exhibit single CPL and it remains challenging to develop organic molecules with dual CPL. Herein, novel through-space conjugated chiral foldamers are constructed by attaching two biphenyl arms to the 9,10-positions of phenanthrene, and switchable dual CPL with opposite signs at different emission wavelengths are successfully realized in the foldamers containing high-polarizability substitutes (cyano, methylthiol and methylsulfonyl). The combined experimental and computational results demonstrate that the intramolecular through-space conjugation has significant contributions to stabilizing the folded conformations. Upon photoexcitation in high-polar solvents, strong interactions between the biphenyl arms substituted with cyano, methylthio or methylsulfonyl and the polar environment induce conformation transformation for the foldamers, resulting in two transformable secondary structures of opposite chirality, accounting for the dual CPL with opposite signs. These findings highlight the important influence of the secondary structures on the chiroptical property of the foldamers and pave a new avenue towards efficient and tunable dual CPL materials.

Purely Organic Room-Temperature Phosphorescence Molecule for High-Performance Non-Doped Organic Light-Emitting Diodes.

Purely organic molecules with room-temperature phosphorescence (RTP) are potential luminescent materials with high exciton utilization for organic light-emitting diodes (OLEDs), but those exhibiting superb electroluminescence (EL) performances are rarely explored, mainly due to their long phosphorescence lifetimes. Herein, a robust purely organic RTP molecule, 3,6-bis(5-phenylindolo[3,2-a]carbazol-12(5H)-yl)-xanthen-9-one (3,2-PIC-XT), is developed. The neat film of 3,2-PIC-XT shows strong green RTP with a very short lifetime (2.9 µs) and a high photoluminescence quantum yield (72 %), and behaviors balanced bipolar charge transport. The RTP nature of 3,2-PIC-XT is validated by steady-state and transient absorption and emission spectroscopies, and the working mechanism is deciphered by theoretical simulation. Non-doped multilayer OLEDs using thin neat films of 3,2-PIC-XT furnish an outstanding external quantum efficiency (EQE) of 24.91 % with an extremely low roll-off (1.6 %) at 1000 cd m-2. High-performance non-doped top-emitting and tandem OLEDs are also achieved, providing remarkable EQEs of 24.53 % and 42.50 %, respectively. Delightfully, non-doped simplified OLEDs employing thick neat films of 3,2-PIC-XT are also realized, furnishing an excellent EQE of 17.79 % and greatly enhanced operational lifetime. The temperature-dependent and transient EL spectroscopies demonstrate the electrophosphorescence attribute of 3,2-PIC-XT. These non-doped OLEDs are the best devices based on purely organic RTP materials reported so far.

Free Radical-Mediated Intramolecular Photocyclization of AIEgens Based on 2,3-Diphenylbenzo[b]thiophene S,S-Dioxide.

As an important category of photochemical reactions, photocyclization is regarded as an ideal entry point for building intelligent photoresponsive materials. Herein, a series of aggregation-induced emission luminogens (AIEgens) with sensitive photoresponsive behavior are developed based on 2,3-diphenylbenzo[b]thiophene S,S-dioxide (DP-BTO), and the impacts of substituents with different electronic structures are investigated. The comprehensive experimental and computational characterizations reveal that their photoresponsive activity is resulted from triplet diradical-mediated intramolecular photocyclization, followed by dehydrogenation to yield stable polycyclic photoproducts. This photocyclization process is active in solution but suppressed in the solid state, and thus can act as a supplementary nonradiative decay channel for the excited state to contribute to AIE effect. Moreover, the generated triplet diradical intermediates upon light irradiation can effectively inhibit the growth of S. aureus, indicative of their promising application as antibacterial agents. This work provides an in-depth mechanistic description about the photocyclization of DP-BTO derivatives and furnishes a perspective on the correlation of photochemical decay and photophysical property.

De Novo Synthesis of α-Oligo(arylfuran)s and Its Application in OLED as Hole-Transporting Material.

Tuning the photophysical properties of π-conjugated oligomers by functionalization of skeleton, to achieve an optically and electronically advantageous building block for organic semiconductor materials is a vital yet challenging task. In this work, a series of structurally well-defined polyaryl-functionalized α-oligofurans, in which aryl groups are introduced precisely into each of the furan units, are rapidly and efficiently synthesized by de novo metal-free synthesis of α-bi(arylfuran) monomers for the first time. This new synthetic strategy nicely circumvents the cumbersome substituent introduction process in the later stage by the preinstallation of the desired aryl groups in the starting material. The characterization of α-oligo(arylfuran)s demonstrates that photoelectric properties of coplanar α-oligo(arylfuran)s can be tuned through varying aryl groups with different electrical properties. These novel α-oligo(arylfuran)s have good hole transport capacity and can function as hole-transporting layers in organic light-emitting diodes, which is indicative of significant breakthrough in the application of α-oligofurans materials in OLEDs. And our findings offer an avenue for the ingenious use of α-oligo(arylfuran)s as p-type organic semiconductors for OLEDs.

Bright Organic Mechanoluminescence and Remarkable Mechanofluorochromism from Circularly Polarized TADF Enantiomers with Aggregation-Induced Emission Properties.

The development of circularly polarized thermally activated delayed fluorescence (CP-TADF) luminogens with stimuli-response characteristics remains challenging. Herein, a pair of organic enantiomers, S-CzTA and R-CzTA, with aggregation-induced emission properties, have been successfully developed by introducing chiral 1,2,3,4-tetrahydronaphthalene and carbazole to phthalimide. They present CP-TADF properties in toluene solutions, giving dissymmetric factors of 0.84×10-3 and -1.03×10-3 , respectively. In the crystalline state, both S-CzTA and R-CzTA can emit intense blue TADF and produce very bright sky-blue mechanoluminescence (ML) and remarkable mechanofluorochromism (MFC) under the stimuli of mechanical force. Single-crystal analysis and theoretical calculation results suggest that their ML activities are probably associated with their chiral and polar molecular structures and unique non-centrosymmetric molecular packing modes. Furthermore, the MFC properties of the enantiomers likely originate from the destruction of crystal structure, leading to the planarization of molecular conformation. This work may provide helpful guidance for developing new CP-TADF materials with force-stimuli-responsive properties.

Efficient Circularly Polarized Electroluminescence from Achiral Luminescent Materials.

Circularly polarized electroluminescence (CP-EL) is generally produced in organic light-emitting diodes (OLEDs) based on special CP luminescent (CPL) materials, while common achiral luminescent materials are rarely considered to be capable of direct producing CP-EL. Herein, near ultraviolet CPL materials with high photoluminescence quantum yields and good CPL dissymmetry factors are developed, which can induce blue to red CPL for various achiral luminescent materials. Strong near ultraviolet CP-EL with the best external quantum efficiencies (ηext s) of 9.0 % and small efficiency roll-offs are achieved by using them as emitters for CP-OLEDs. By adopting them as hosts or sensitizers, commercially available yellow-orange achiral phosphorescence, thermally activated delayed fluorescence (TADF) and multi-resonance (MR) TADF materials can generate intense CP-EL, with high dissymmetry factors and outstanding ηext s (30.8 %), demonstrating a simple and universal avenue towards efficient CP-EL.

Achieving Multiple Quantum-Interfered States via Through-Space and Through-Bond Synergistic Effect in Foldamer-Based Single-Molecule Junctions.

The construction of multivalued logic circuits by multiple quantum-interfered states at the molecular level can make full use of molecular diversity and versatility, broadening the application of molecular electronics. Understanding charge transport through different conducting pathways and how they interact with each other in molecules with a secondary structure is an indispensable foundation to achieve this goal. Herein, we elucidate the synergistic effect from through-space and through-bond conducting pathways in foldamers derived from ortho-pentaphenylene by the separate modulation on these pathways. The shrinkage of central heterocycles' sizes allows foldamers to stack with larger overlap degrees, resulting in level-crossing and thus transformation from constructive quantum interference (CQI) to destructive quantum interference (DQI) in a through-space pathway. The alteration of central heterocycles' connection sites enhances through-bond conjugation, leading to amplified contribution from a through-bond pathway. The enhanced through-bond pathway destructively interferes with the through-space pathway, exerting a suppression effect on transmission. Therefore, four quantum-interfered states of through-space and through-bond combination are generated, including through-space CQI-dominated states, through-space DQI-dominated states, through-space CQI states with through-bond suppression, and through-space DQI states with through-bond suppression. These findings enable us to regulate charge transport within high-order structures via multiple conducting pathways and provide a proof of concept to construct multivalued logic circuits.

Precisely Detecting the Telomerase Activities by an AIEgen Probe with Dual Signal Outputs after Cell-Cycle Synchronization.

By maintaining the telomere lengths, telomerase can make the tumor cells avoid the apoptosis, thus, achieving the cell immortalization. In the past, a series of telomerase detection systems have been developed through utilizing the unique characteristic of telomerase extended primer. However, fluctuation of telomerase activity, along with the cell cycle progression, leads to ambiguous detection results. Here, we reported a dual signal output detection strategy based on cell-cycle synchronization for precisely detecting telomerase activities by using a new AIEgen probe SSNB. Experimental and simulating calculation results demonstrated that positively charged SSNB could interact with DNA through the electrostatic interaction and π-π interaction, as well as the hydrogen bonds. The aggregation of SSNB caused by the extended template strand primer (TP) could be observed in tumor cells, thus, indicating the telomerase activity in various cell lines. Furthermore, after cell cycle synchronization, it was found that the telomerase activity in the S phase was the highest, no matter from the fluorescence intensity or the ROS generation situation. Dual signal outputs of SSNB verified the significance and necessity of cell-cycle synchronization detection for telomerase activity. This strategy could open a new window for the biotargets of which activity is variational in time dimension.

Effective Therapy of Drug-Resistant Bacterial Infection by Killing Planktonic Bacteria and Destructing Biofilms with Cationic Photosensitizer Based on Phosphindole Oxide.

Developing effective therapies to fight against biofilm-associated infection is extremely urgent. The complex environment of biofilm forces the bacteria to evade the elimination of antibiotics, resulting in recalcitrant chronic infections. To address this issue, a cationic antibacterial agent based on phosphindole oxide (ß-PM-PIO) is designed and prepared. The unique molecular structure endows ß-PM-PIO with aggregation-induced emission feature and efficient singlet oxygen generation ability. ß-PM-PIO shows excellent visual diagnostic function to planktonic bacteria and biofilm. In addition, owing to the synergistic effect of phototoxicity and dark toxicity, ß-PM-PIO can achieve superb antibacterial and antibiofilm performance against Gram-positive bacteria with less potential of developing drug resistance. Notably, ß-PM-PIO also holds excellent anti-infection capacity against drug-resistant bacteria in vivo with negligible side effects. This work offers a promising platform to develop advanced antibacterial agents against multidrug-resistant bacterial infection.

Switchable Circularly Polarized Signals with High Asymmetric Factor Triggered by Dual Photonic Bandgap Structure.

Currently, the smart photonic materials that can switch circularly polarized signals in real-time have attracted extensive attention due to numerous potential applications in information storage and photonics displays. However, the dynamically reversible switching of circularly polarized signals requires precise structural reconfiguration, which is rarely achieved in traditional biomaterials. Herein, a dual photonic bandgap (PBG) structure is constructed based on the optical propagation principle of cellulose-based photonic crystals, enabling the flexible switching of the intensity, wavelength, and direction of circularly polarized luminescence (CPL). By adjusting the fluorescence intensity and the matching degree of chiral structure, the asymmetric factor value of dual PBG structure is up to -1.47, far exceeding other cellulose-based materials. Importantly, it is demonstrated that dual CPL emission can be efficiently induced by two different PBGs, opening a new approach for on-demand switching of single and dual CPL emission. In addition, the dual PBG structure exhibits dual circularly polarized reflected signals under the circular polarizer, which perfectly embodies the applicability of multiple encryptions in QR codes. This work provides new insights into the real-time manipulation of circularly polarized signals by chiral photonic materials.

Red Light-Emitting Thermally-Activated Delayed Fluorescence of Naphthalimide-Phenoxazine Electron Donor-Acceptor Dyad: Time-Resolved Optical and Magnetic Spectroscopic Studies.

We prepared an orthogonal compact electron-donor (phenoxazine, PXZ)-acceptor (naphthalimide, NI) dyad (NI-PXZ), to study the photophysics of the thermally-activated delayed fluorescence (TADF), which has a luminescence lifetime of 16.4 ns (99.2 %)/17.0 µs (0.80 %). A weak charge transfer (CT) absorption band was observed for the dyad, indicating non-negligible electronic coupling between the donor and acceptor at the ground state. Femtosecond transient absorption spectroscopy shows a fast charge separation (CS) (ca. 2.02∼2.72 ps), the majority of the singlet CS state is short-lived, especially in polar solvents (τCR = 10.3 ps in acetonitrile, vs. 1.83 ns in toluene, 7.81 ns in n-hexane). Nanosecond transient absorption spectroscopy detects a long-lived transient species in n-hexane, which is with a mixed triplet local excited state (3 LE) and charge separated state (3 CS), the lifetime is 15.4 µs. In polar solvents, such as tetrahydrofuran and acetonitrile, a neat 3 CS state was observed, whose lifetimes are 226 ns and 142 ns, respectively. Time-resolved electron paramagnetic resonance (TREPR) spectra indicate the existence of strongly spin exchanged 3 LE/3 CT states, with the effective zero field splitting (ZFS) |D| and |E| parameters of 1484 MHz and 109 MHz, respectively, much smaller than that of the native 3 NI state (2475 and 135 MHz). It is rare but solid experimental evidence that a closely-lying 3 LE state is crucial for occurrence of TADF and this 3 LE state is an essential intermediate state to facilitate reverse intersystem crossing in TADF systems.

Modulating the intersystem crossing mechanism of anthracene carboxyimide-based photosensitizers via structural adjustments and application as a potent photodynamic therapeutic reagent.

Herein, a series of compact anthracene carboxyimide (ACI) based donor-acceptor dyads were prepared by substituting bulky aryl moieties with various electron-donating ability to study the triplet-excited state properties. The ISC mechanism and triplet yield of the dyads were successfully tuned via structural manipulation. Efficient ISC (ΦΔ ≈ 99%) and long-lived triplet state (τT ≈ 122 µs) was observed for the orthogonal anthracene-labeled ACI derivative compared to the Ph-ACI and NP-ACI dyads, which showed fast triplet state decay (τT ≈ 7.7 µs). Femtosecond transient absorption study demonstrated the ultrafast charge separation (CS) and efficient charge recombination (CR) in the orthogonal dyads and ISC occurring via spin-orbit charge transfer (SOCT) mechanism (AN-ACI: τCS = 355 fs, τCR = 2.41 ns; PY-ACI: τCS = 321 fs, τCR = 1.61 ns), while in Ph-ACI and NP-ACI dyads triplet populate following the normal ISC channel (nπ* → ππ* transition), no CS was observed. We found that the attachment of suitable aryl donor moiety (AN- or PY-) to the ACI core can ensure the insertion of the intermediate triplet state, resulting in a small energy gap among charge separated state (CSS) and triplet state, which leads to efficient ISC in these derivatives. The SOCT-ISC-based AN-ACI dyad was confirmed to be a potent photodynamic therapeutic reagent; an ultra-low IC50 value (0.27 nM) that was nearly 214 times lower than that of the commercial Rose Bengal photosensitizer (57.8 nM) was observed.

Robust Luminescent Molecules with High-Level Reverse Intersystem Crossing for Efficient Near Ultraviolet Organic Light-Emitting Diodes.

Organic light-emitting diodes (OLEDs) radiating near ultraviolet (NUV) light are of high importance but rarely reported due to the lack of robust organic short-wavelength emitters. Here, we report a short π-conjugated molecule (POPCN-2CP) with high thermal and morphological stabilities and strong NUV photoluminescence. Its neat film exhibits an electroluminescence (EL) peak at 404 nm with a maximum external quantum efficiency (ηext,max ) of 7.5 % and small efficiency roll-off. The doped films of POPCN-2CP in both non-polar and polar hosts at a wide doping concentration range (10-80 wt%) achieve high-purity NUV light (388-404 nm) and excellent ηext,max s of up to 8.2 %. The high-level reverse intersystem crossing improves exciton utilization and accounts for the superb ηext,max s. POPCN-2CP can also serve as an efficient host for blue fluorescence, thermally activated delayed fluorescence and phosphorescence emitters, providing excellent EL performance via Förster energy transfer.