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In purely organic room‐temperature phosphorescence (RTP) materials, fluorescence radiative transitions generally compete against inter‐system crossing (ISC) transitions to give fluorescence/phosphorescence dual emission. In order to achieve pure phosphorescence in RTP organic light‐emitting diodes (OLEDs), extended π‐conjugation is introduced into Se‐containing donors to suppress the fluorescence radiative transitions by the symmetry excited state orbitals in the introduced π–π* transitions that cancel the overlap of the orbitals, and two novel nonaromatic amine donor containing orange RTP emitters namely 2‐(benzo[c]phenoxaselenin‐10‐yl)‐4,6‐diphenyl‐1,3,5‐triazine (BPXSeDRZ) and 2‐(dibenzo[a,c]phenoxaselenin‐11‐yl)‐4,6‐diphenyl‐1,3,5‐triazine (DBPXSeDRZ) are developed, both of which exhibit efficient orange pure phosphorescence in doped films thanks to the sufficient ISC transitions. As a result, high external quantum efficiencies of 17.2% and 17.9% are respectively achieved for the orange RTP‐OLEDs based on BPXSeDRZ and DBPXSeDRZ for the first time, and they also exhibit stable pure electro‐phosphorescence spectra in a wide driving voltage. Moreover, by adopting DBPXSeDRZ as a sensitizer to harvest the triplet excitons and tetraphenyldibenzoperiflanthene as a conventional fluorescent emitter, the external quantum efficiency of the sensitized red fluorescent OLED can be elevated to 10.1%, which greatly expands the potential applications of the metal‐free phosphors in OLEDs. [ABSTRACT FROM AUTHOR]

Polychlorinated (hetero)arenes have shown great promise for organic optoelectronics applications. However, the harsh synthetic routes for polychlorinated compounds and the possible luminescence quenching from the compact intermolecular π–π stacking induced by chlorine atoms limit their investigations and applications in luminescent materials. Herein, two isomeric polychlorinated polycyclic aromatic hydrocarbon (PAH) compounds JY‐1‐Cl and JY‐2‐Cl consisting of rigidified aryl ketones and amine are designed and synthesized under mild conditions through nucleophilic chlorination intermediated by an electron donor‐acceptor complex. Among them, as a result of the strong π–π interactions induced by chlorine atoms, JY‐2‐Cl exhibits bright monomer and dimer emissions with dual thermally activated delayed fluorescence (TADF) characters. Notably, compared with the non‐chlorinated compounds, a high photoluminescence quantum yield is maintained after introducing multiple chlorine atoms into JY‐2‐Cl. The first dual‐TADF organic light‐emitting diodes are also successfully fabricated with maximum external quantum efficiency as high as 29.1 % by employing JY‐2‐Cl as emitter. This work presents a new paradigm and synthesis of polychlorinated amine‐carbonyl PAHs and demonstrates the great potential of the chlorinated materials for luminescent applications. [ABSTRACT FROM AUTHOR]

High‐quality hosts are indispensable for simultaneously realizing stable, high efficiency, and low roll‐off blue solution‐processed organic light‐emitting diodes (OLEDs). Herein, three solution processable bipolar hosts with successively reduced triplet energies approaching the T1 state of thermally activated delayed fluorescence (TADF) emitter are developed and evaluated for high‐performance blue OLED devices. The smaller T1 energy gap between host and guest allows the quenching of long‐lived triplet excitons to reduce exciton concentration inside the device, and thus suppresses singlet‐triplet and triplet‐triplet annihilations. Triplet‐energy‐mediated hosts with high enough T1 and better charge balance in device facilitate high exciton utilization efficiency and uniform triplet exciton distribution among host and TADF guest. Benefited from these synergetic factors, a high maximum external quantum efficiency (EQEmax) of 20.8%, long operational lifetime (T50 of 398.3 h @ 500 cd m−2), and negligible efficiency roll‐off (EQE of 20.1% @ 1000 cd m−2) are achieved for bluish‐green TADF OLEDs. Additionally introducing a narrowband emission multiple‐resonance TADF material as terminal emitter to accelerate exciton dynamic and improve exciton utilization, a higher EQEmax of 23.1%, suppressed roll‐off and extended lifetime of 456.3 h are achieved for the sky‐blue sensitized OLEDs at the same brightness. [ABSTRACT FROM AUTHOR]

Purely organic room‐temperature phosphorescence (RTP) materials generally exhibit low phosphorescence quantum yield (ϕP) and long phosphorescence lifetime (τP) due to the theoretically spin‐forbidden triplet state. Herein, by introducing a donor–acceptor (D–A) skeleton with a phenoxaselenine donor, three nonaromatic amine donor containing compounds with high ϕP and short τP in amorphous films are developed. Besides the enhanced spin–orbit coupling (SOC) by the heavy‐atom effect of selenium, the D–A skeleton which facilitates orbital angular momentum change can further boost SOC, and severe nonradiative energy dissipation is also suppressed by the rigid molecular structure. Consequently, a record‐high external quantum efficiency of 19.5% are achieved for the RTP organic light‐emitting diode (OLED) based on 2‐(phenoxaselenin‐3‐yl)‐4,6‐diphenyl‐1,3,5‐triazine (PXSeDRZ). Moreover, voltage‐dependent color‐tunable emission and single‐molecule white emission are also realized. These results shed light on the broad prospects of purely organic phosphorescence materials as highly efficient OLED emitters especially for potential charming lighting applications. [ABSTRACT FROM AUTHOR]

Chirality is a magical property that exists in nature universally, ranging from the spin of microscopic electrons to the galaxies. Furthermore, circularly polarized organic electroluminescent materials have promising prospects in improving the brightness of displays, but there are still some problems. At present, most of chiral thermally activated delayed fluorescence small molecules show relatively low circularly polarized luminescence (CPL) dissymmetry factors between 10−4 and 10−3 because of the electric dipole‐allowed but magnetic dipole‐forbidden transition of the singlet state. In this work, a promising strategy is reported for constructing chiral exciplex systems with a chiral electron acceptor and a regular achiral donor to achieve high CPL dissymmetry factors in both photoluminescence and electroluminescence. From theoretical calculation results, the exciplex systems possess a large separation of the highest occupied molecular orbital and the lowest unoccupied molecular orbital in donor and acceptor molecules, respectively, which results in comparable electric and magnetic transition dipole moments. The resultant CPL organic light‐emitting diodes based on the exciplex systems as emitters show low turn‐on voltage of 2.4 V, high external quantum efficiencies of 12.7% and 9.3%, and opposite circularly polarized electroluminescence with high dissymmetry factors (gEL) of +7.25 × 10−3 and −9.89 × 10−3. [ABSTRACT FROM AUTHOR]

Generally, the charge transfer character of thermally activated delayed fluorescence (TADF) materials results in a long excitonic lifetime and broad‐band emission. With the combination of unity exciton utilization of TADF material and high radiative rate and narrow‐band emission of conventional fluorescence (CF) dopant, hyperfluorescence organic light‐emitting diodes (HF‐OLEDs) attract extensive attention in industry and academia recently. Till now, Dexter energy transfer (DET) from the triplet state of TADF assistant host to the dark triplet state of CF guest is the top‐drawer energy loss issue root in HF‐OLEDs. Herein, the energy loss of DET is blocked through one‐step substitution of TADF assistant host by electronically inert phenyl‐fluorene terminal for the first time. The blocking effect on DET process in HF‐OLEDs is investigated by means of photophysical characterization, theoretical calculation, device fabrication, and Monte Carlo simulation. The maximum external quantum efficiency of 18.1% with Commission Internationale de L'Eclairage coordinates of (0.61, 0.38) is achieved, which is on par with the state‐of‐the‐art efficiency for red HF‐OLEDs. This work presents a feasible design strategy for TADF assistant host aimed at achieving highly efficient HF‐OLEDs with narrow‐band emission. [ABSTRACT FROM AUTHOR]

Highly efficient organic thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) emitters for organic light‐emitting diodes (OLEDs) generally consist of a twisted donor–acceptor skeleton with aromatic amine donors. Herein, through introducing sulfur atoms into isomeric pentaphene and pentacene frameworks, we demonstrate a set of polycyclic luminophores exhibiting efficient TADF and RTP characters. The incorporation of sulfur atoms confirms a folded molecular plane, while intensifies singlet–triplet spin‐orbit coupling. Further, the isomeric effect has a significant effect on the electronic structure of excited state, giving rise to the investigated compounds tunable luminescence mechanisms of TADF and RTP. With efficient triplet harvesting ability, maximum external quantum efficiencies up to 25.1 % and 8.7 % are achieved for the corresponding TADF and RTP OLEDs, verifying the great potential of sulfur‐bridged frameworks for highly efficient devices. [ABSTRACT FROM AUTHOR]

A series of pure organic halogenated hexaphenylmelamine (HPM) derivatives featuring remarkably weakened ultralong room-temperature phosphorescence (RTP) were meticulously investigated. As the p-substituted atoms of these HPM derivatives sequentially changed from H to F, Cl and Br, both the RTP lifetimes and efficiencies dramatically decreased from 608 ms with 13.4% (HPM-H) to 337 ms with 5.3% (HPM-F), 99 ms with 1.3% (HPM-Cl), and 2.8 ms with undetectable efficiency (HPM-Br), respectively. Most notably, the severely weakened efficiencies are fundamentally different from the trends of the effect of halogenation on phosphorescence properties previously reported. Coupled with experimental results and theoretical simulations, the subtle change of molecular packing induced by halogenation should be responsible for the distinctive RTP properties. This finding not only provides a unique halogen-involved RTP phenomenon, but also offers a very special perspective to understand the effect of halogenation on phosphorescence. [ABSTRACT FROM AUTHOR]

The effect of boronic ester substitution on the room-temperature phosphorescence properties of phenoxathiine-based derivatives was thoroughly investigated. A significantly improved phosphorescence quantum efficiency of up to 20% in the crystalline state was achieved by delicate molecular manipulation for both enhanced spin–orbital coupling and compact intermolecular packing. [ABSTRACT FROM AUTHOR]

• Hosts with TADF, conventional fluorescence and RTP characters are developed. • Exciton utilization efficiency is improved by the host with TADF character. • An EQE of 36.1% was achieved for sky blue OLED with DspiroAc-TRZ as emitter. • An EQE of 34.0% was achieved for the sensitized device with v -DABNA dopant. Spiral donor units have attracted extensive research focuses in designing highly emissive thermally activated delayed fluorescence (TADF) emitters. Herein, to reveal the significance of spiral donor units for constructing highly efficient host materials, several spiral donor-based host materials are developed. With the incorporation of spiral donor, increased intermolecular distance is achieved to reduce the concentration quenching effect of dopant. Moreover, the high triplet energy level of spiral donor can provide an additional energy transfer channel to further improve the device performance. Noteworthy, by connecting spiral donors or conventional carbazole unit with different electron-withdrawing units phenoxathiine 10,10-dioxide (PX) or phenoxathiine (PA), these hosts are given different photophysical properties of TADF, room-temperature phosphorescence (RTP) and conventional fluorescence (CF). The strong electron-withdrawing ability of PX is beneficial to the TADF character of spiral donor-based molecules, while the weak electron-withdrawing ability of PA is beneficial to the RTP property. Consequently, the blue OLEDs with DspiroAc-TRZ as a dopant emitter based on the hosts with TADF characters exhibit higher performance than those with RTP and CF properties, and excellent external quantum efficiency (EQE) of 36.1 % and current efficiency of 84.6 cd/A are achieved in a simple device structure. Furthermore, peak EQEs of 34.0 % and 33.0 % are achieved, when DspiroS-PX and DspiroS-PA hosted DspiroAc-TRZ are used to sensitize blue multi-resonance TADF emitter v -DABNA. Our work may shed new light on designing highly efficient host materials for TADF emitters. [ABSTRACT FROM AUTHOR]

Chirality is a magical property that exists in nature universally, ranging from the spin of microscopic electrons to the galaxies. Furthermore, circularly polarized organic electroluminescent materials have promising prospects in improving the brightness of displays, but there are still some problems. At present, most of chiral thermally activated delayed fluorescence small molecules show relatively low circularly polarized luminescence (CPL) dissymmetry factors between 10−4 and 10−3 because of the electric dipole‐allowed but magnetic dipole‐forbidden transition of the singlet state. In this work, a promising strategy is reported for constructing chiral exciplex systems with a chiral electron acceptor and a regular achiral donor to achieve high CPL dissymmetry factors in both photoluminescence and electroluminescence. From theoretical calculation results, the exciplex systems possess a large separation of the highest occupied molecular orbital and the lowest unoccupied molecular orbital in donor and acceptor molecules, respectively, which results in comparable electric and magnetic transition dipole moments. The resultant CPL organic light‐emitting diodes based on the exciplex systems as emitters show low turn‐on voltage of 2.4 V, high external quantum efficiencies of 12.7% and 9.3%, and opposite circularly polarized electroluminescence with high dissymmetry factors (gEL) of +7.25 × 10−3 and −9.89 × 10−3. [ABSTRACT FROM AUTHOR]

It is an immense challenge to develop efficient long-wavelength (orange-to-red) thermally activated delayed fluorescence (TADF) materials due to the increasing nonradiative decay rates following the energy-gap law. Herein, two pairs of asymmetric isomers; DPyPzTPA and TPAPzDPy, and PyPzDTPA and DTPAPzPy based on electron-deficient moieties dibenzo[ a,c ]phenazine (Pz) and pyridine (Py) combined with electron-donor units of triphenylamine (TPA) were designed and synthesized. Their photophysical properties could be finely modulated by changing the position and number of Py groups as well as TPA fragments onto Pz cores. DPyPzTPA and DTPAPzPy possess much more rigidity and thus less geometry relaxation and non-radiative decay between ground states and excited states than those of PyPzDTPA and TPAPzDPy. Intriguingly, DPyPzTPA exhibits the highest relative photoluminescence quantum yield (Φ PL) and the fastest reverse intersystem crossing (rISC) rate among them owing to relatively stronger rigidity and spin-orbit coupling (SOC) interactions between the lowest singlet (S 1) and energetically close-lying excited triplet state and therefore, the device showed the highest maximum external quantum efficiency (EQE max) of 16.6% (60.9 lm/W, 53.3 cd/A) with Commission Internationale de I'Eclairage (CIE) coordinates of (0.43, 0.55), peak wavelength 556 nm. In stark contrast, due to its lower rigidity and extremely weak delayed fluorescence (DF) characteristic and thus the much lower Φ PL , TPAPzDPy-based devices are only half as efficient (30.8 lm/W, 27.5 cd/A, 8.3% EQE) despite the isomers possessing equal singlet-triplet energy gaps (Δ E ST) of 0.43 eV. On the other hand, the device based on DTPAPzPy also demonstrated a strongly enhanced performance (59.1 lm/W, 52.7 cd/A, 16.1% EQE) than its isomer PyPzDTPA-based device (39.5 lm/W, 35.2 cd/A, 10.3% EQE). This work explicitly implicates that the asymmetric and isomeric molecular design is a potential strategy for promoting the development of highly efficient long-wavelength TADF materials. • Four emitters based on pyridine-decorated dibenzo[ a,c ]phenazine were developed. • Their photophysical properties could be finely modulated. • DPyPzTPA exhibits the largest Φ PL of 59.1% and k rISC of 1.48 × 103 S−1. • DPyPzTPA's device showed the highest efficiency of 60.9 lm/W, 53.3 cd/A and 16.6%. [ABSTRACT FROM AUTHOR]

• NIR-emitting Ir complexes with rigid benzo[a]indolo[3,2-c]phenazine (BIPz) were obtained. • The effect of pendent groups at BIPz on photophysical and EL properties of Ir complexes is investigated. • Ir-2 complex with ter t-butyl instead of methyl pendant exhibits better EL properties at 746 nm. • The Ir-2-doped PLED displays an increasing EQE of 2.65% with a radiant emittance of 13057 mW Sr−1 m−2. Two near-infrared (NIR)-emitting iridium(III) complexes of (Me-BIPz) 2 Ir(acac) and (t Bu-BIPz) 2 Ir(acac), (i.e. Ir-1 and Ir-2) are designed and synthesized, which contain methyl and t -butyl substituted 14-phenyl-14H-benzo[a]indolo[3,2-c]phenazine (BIPz), respectively with a rigid D-A-type coordinated core. The influence of the rigid D-A skeleton and the attached groups on photoelectronic properties of iridium complexes is primarily investigated. An advanced external quantum efficiency (EQE) of 2.65% with a radiant emittance of 13057 mW Sr−1 m−2 at 746 nm is obtained in the Ir-2 -doped polymer light-emitting devices. This EQE value is 1.5 times higher than that in the Ir-1 -doped devices. Furthermore, this type of iridium complexes exhibits better NIR-emitting properties than most of the reported iridium complexes containing the C^N ligand with two coordinated aryl rings. The results indicate that the rigid coordinated core of C^N ligand is an effective strategy to construct high-efficiency NIR-emitting iridium complexes. Two iridium complexes of (t Bu-BIPz) 2 Ir(acac) and (Me-BIPz) 2 Ir(acac) are designed and synthesized by employing benzo[a]indolo[3,2-c]phenazine (BIPz) as a rigid coordinated core. Intense near-infrared EL at 746 nm with an increasing EQE of 2.65% is observed in the (t Bu-BIPz) 2 Ir(acac)-doped PLEDs Image, graphical abstract [ABSTRACT FROM AUTHOR]