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Deep‐red/near‐infrared (DR/NIR) organic light‐emitting diodes (OLEDs) are promising for applications such as night‐vision readable marking, bioimaging, and photodynamic therapy. To tune emission spectra into the DR/NIR region, red emitters generally require assistance from intermolecular interactions. But such interactions generally lead to sharp efficiency declines resulting from unwanted quenching events. To overcome this challenge, herein, an advanced method via strategically managing the intermolecular interactions of thermally activated delayed fluorescence (TADF) emitters is proposed. The proof‐of‐concept molecule called DCN‐SPTPA exhibits impressive resistance to quenching while delivering controllable aggregation behavior for redshifting the emission by installing an end‐spiro group. Consequently, two emitters demonstrate similar photophysical properties and device performance at very low doping levels; while DCN‐SPTPA‐based OLEDs demonstrate a 1.3–1.4‐fold enhancement of the external quantum efficiencies (EQEs) with respect to the control molecule at 5–20 wt.% doping ratios, affording DR/NIR emission at 656, 688, 696, and 716 nm with record‐breaking EQEs of 36.1%, 29.3%, 28.2%, and 24.0%, respectively. Moreover, DCN‐SPTPA‐based nondoped NIR device also retains a state‐of‐the‐art EQE of 2.61% peaked at 800 nm. This work first demonstrates instructive guidance for accurately manipulating the intermolecular interactions of red TADF emitters, which will spur future developments in high‐performance DR/NIR OLEDs. [ABSTRACT FROM AUTHOR]

Hindered by spectral broadening issues with redshifted emission, long‐wavelength (e.g. maxima beyond 570 nm) multiple resonance (MR) emitters with full width at half maxima (FWHMs) below 20 nm remain absent. Herein, by strategically embedding diverse boron (B)/nitrogen (N) atomic pairs into a polycyclic aromatic hydrocarbon (PAH) skeleton, we propose a hybrid pattern for the construction of a long‐wavelength narrowband MR emitter. The proof‐of‐concept emitter B4N6‐Me realized orange‐red emission with an extremely small FWHM of 19 nm (energy unit: 70 meV), representing the narrowest FWHM among all reported long‐wavelength MR emitters. Theoretical calculations revealed that the cooperation of the applied para B‐π‐N and para B‐π‐B/N‐π‐N patterns is complementary, which gives rise to both narrowband and redshift characteristics. The corresponding organic light‐emitting diode (OLED) employing B4N6‐Me achieved state‐of‐the‐art performance, e.g. a narrowband orange‐red emission with an FWHM of 27 nm (energy unit: 99 meV), an excellent maximum external quantum efficiency (EQE) of 35.8 %, and ultralow efficiency roll‐off (EQE of 28.4 % at 1000 cd m−2). This work provides new insights into the further molecular design and synthesis of long‐wavelength MR emitters. [ABSTRACT FROM AUTHOR]

Building blocks and heteroatom alignments are two determining factors in designing multiple resonance (MR)‐type thermally activated delayed fluorescence (TADF) emitters. Carbazole‐fused MR emitters, represented by CzBN derivatives, and the heteroatom alignments of ν‐DABNA are two star series of MR‐TADF emitters that show impressive performances from the aspects of building blocks and heteroatom alignments, respectively. Herein, a novel CzBN analog, Π‐CzBN, featuring ν‐DABNA heteroatom alignment is developed via facile one‐shot lithium‐free borylation. Π‐CzBN exhibits superior photophysical properties with a photoluminescence quantum yield close to 100 % and narrowband sky blue emission with a full width at half maximum (FWHM) of 16 nm/85 meV. It also gives efficient TADF properties with a small singlet‐triplet energy offset of 40 meV and a fast reverse intersystem crossing rate of 2.9×105 s−1. The optimized OLED using Π‐CzBN as the emitter achieves an exceptional external quantum efficiency of 39.3 % with a low efficiency roll‐off of 20 % at 1000 cd m−2 and a narrowband emission at 495 nm with FWHM of 21 nm/106 meV, making it one of the best reported devices based on MR emitters with comprehensive performance. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters are very promising in the high‐resolution and high‐efficiency displays, due to their narrow and highly efficient optical emissions. Early MR‐TADF cores that show only short‐range charge‐transfer (CT) electronic excitations hardly afford ideal performances (e.g., show low efficiencies) in organic light‐emitting diodes (OLEDs). This work thus designs and synthesizes two MR‐TADF emitters (TCzBN‐BP and TCzBN‐FP), where the same MR core TCzBN is chemically modified by the acceptor fragments benzophenone/9‐fluorenone (BP/FP) to incorporate long‐range CT excitations in the two molecules. OLEDs exploiting TCzBN‐BP as emitter, in which short‐range CT excitation is dominant in the first singlet (S1) excited state, achieve a maximum external quantum efficiency (EQE) of 35.6% and a narrow emission bandwidth of 35 nm. In contrast, OLEDs exploiting TCzBN‐FP with an overloaded long‐range CT excitation in the S1 state exhibit a maximum EQE of 27.2% and a broadened emission bandwidth of 56 nm. This work not only shows the importance of careful management of long‐ and short‐range CT excitations, but also provides a new insight into the structure–property relationship in the MR‐TADF emitters, which thus promotes the design of more novel MR‐TADF emitters with high efficiencies and high color purity. [ABSTRACT FROM AUTHOR]

High‐performance nondoped organic light‐emitting diodes (OLEDs) are promising technologies for future commercial applications. Herein, we synthesized two new thermally activated delayed fluorescence (TADF) emitters that enable us, for the first time, to combine three effective approaches for enhancing the efficiency of nondoped OLEDs. First, the two emitters are designed to have high steric hindrances such that their emitting cores will be suitably isolated from those of their neighbors to minimize concentration quenching. On the other hand, each of the two emitters has two stable conformations in solid films. In their neat films, molecules with the minority conformation behave effectively as dopants in the matrix composing of the majority conformation. One hundred percent exciton harvesting is thus theoretically feasible in this unique architecture of "self‐doped" neat films. Furthermore, both emitters have relatively high aspect ratios in terms of their molecular shapes. This leads to films with preferred molecular orientations enabling high populations of horizontal dipoles beneficial for optical out‐coupling. With these three factors, OLEDs with nondoped emitting layers of the respective emitters both achieve nearly 100% exciton utilization and deliver over 30% external quantum efficiencies and ultralow efficiency roll‐off at high brightness, which have not been observed in reported nondoped OLEDs. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) material is currently a research hotspot in organic light‐emitting diodes (OLEDs) due to their high color purity and high exciton utilization. However, there are only a handful of MR‐TADF emitters with emissions beyond the blue‐to‐green region. The very limited emission colors for MR‐TADF emitters are mainly caused by the fact that so far molecular modifications of MR‐TADF do not offer much change in the emission colors. Here, we report a new approach to modifying a prototypical MR core of DABNA by fusing carbazoles to the MR framework. The carbazole‐fused molecule (TCZ‐F‐DABNA) basically maintains the MR‐dominated features of DABNA while red‐shifting the emission. Its OLED achieves an external quantum efficiency of 39.2 % with a peak at 588 nm, which is a record‐high efficiency for OLEDs with peaks beyond 560 nm. This work provides a new approach for significantly tunning emission colors of MR‐TADF emitters. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Red thermally activated delayed fluorescence (TADF) emitters are essential for the development of organic light‐emitting diodes (OLEDs). To better understand and develop red TADF emitters, herein, the effect of quasi‐degenerate orbital distribution was investigated on their performance. Two red TADF emitters 10,10'‐(11,12‐difluorodibenzo[a,c]phenazine‐3,6‐diyl)bis(10H‐phenoxazine) (DPXZ‐BPF) and 10,10',10"‐(12‐fluorodibenzo[a,c]phenazine‐3,6,11‐triyl)tris(10H‐phenoxazine) (TPXZ‐BPF) were constructed by combining two or three phenoxazine (PXZ) donor units with a rigid coplanar acceptor core. As expected, a couple of PXZ units can induce quasi‐degenerate orbital distribution by virtue of the high steric hindrance between each donor unit and acceptor core, which enables multiple excited states engaged in the reverse intersystem crossing (RISC) process. Consequently, DPXZ‐BPF and TPXZ‐BPF exhibit fast RISC rates (kRISCs) of 1.07 × 106 s–1 and 1.29 × 106 s–1 and high PLQYs of 74.6% and 81.1%, respectively. And the higher kRISC and PLQY of TPXZ‐BPF are mainly attributed to the additional quasi‐degenerate orbitals, which further enhance the triplet RISC process and the singlet radiative process. As a result, TPXZ‐BPF‐based OLEDs achieved improved efficiencies with a red‐shifted emission compared with DPXZ‐BPF‐based OLEDs. These results demonstrated the tremendous potential of introducing quasi‐degenerate orbital distribution in developing red TADF emitters. [ABSTRACT FROM AUTHOR]

The conformational distribution and mutual interconversion of thermally activated delayed fluorescence (TADF) emitters significantly affect the exciton utilization. However, their influence on the photophysics in amorphous film states is still not known due to the lack of a suitable quantitative analysis method. Herein, we used temperature‐dependent time‐resolved photoluminescence spectroscopy to quantitatively measure the relative populations of the conformations of a TADF emitter for the first time. We further propose a new concept of "self‐doping" for realizing high‐efficiency nondoped OLEDs. Interestingly, this "compositionally" pure film actually behaves as a film with a dopant (quasi‐equatorial form) in a matrix (quasi‐axial form). The concentration‐induced quenching that may occur at high concentrations is thus expected to be effectively relieved. The "self‐doping" OLED prepared with the newly developed TADF emitter TP2P‐PXZ as a neat emitting layer realizes a high maximum external quantum efficiency of 25.4 % and neglectable efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) provides great potential for the realization of efficient and stable organic light‐emitting diodes (OLEDs). However, it is still challenging for blue TADF emitters to simultaneously achieve high efficiency, high brightness, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) value. Here, the design and synthesis of two new benzonitrile‐based TADF emitters (namely 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐diphenyl‐9H‐carbazol‐9‐yl)benzonitrile (2PhCz2CzBn) and 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)benzonitrile (2tCz2CzBn)) with a symmetrical and rigid heterodonor configuration are reported. The TADF OLEDs doped with both the emitters can achieve a high external quantum efficiency (EQE) over 20% and narrowband blue emission of 464 nm with a CIEy < 0.2. Moreover, the incorporation of a terminal tert‐butyl group can weaken the intermolecular π–π stacking in the nondoped TADF emitter, and thus significantly suppress self‐aggregation‐caused emission quenching for enhanced delayed fluorescence. A peak EQE of 21.6% is realized in the 2tCz2CzBn‐based nondoped device with an extremely low turn‐on voltage of 2.7 V, high color stability, a high brightness over 20 000 cd m−2, a narrow full‐width at half‐maximum of 70 nm, and CIE color coordinates of (0.167, 0.248). [ABSTRACT FROM AUTHOR]

Abstract: A novel molecular model of connecting electron‐donating (D) and electron‐withdrawing (A) moieties via a space‐enough and conjugation‐forbidden linkage (D‐Spacer‐A) is proposed to develop efficient non‐doped thermally activated delayed fluorescence (TADF) emitters. 10‐(4‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl) phenoxy) phenyl)‐9,9‐dimethyl‐9,10‐dihydroacridine (DMAC‐o‐TRZ) was designed and synthesized accordingly. As expected, it exhibits local excited properties in single‐molecule state as D‐Spacer‐A molecular backbone strongly suppress the intramolecular charge‐transfer (CT) transition. And intermolecular CT transition acted as the vital radiation channel for neat DMAC‐o‐TRZ film. As in return, the non‐doped device exhibits a remarkable maximum external quantum efficiency (EQE) of 14.7 %. These results prove the feasibility of D‐Spacer‐A molecules to develop intermolecular CT transition TADF emitters for efficient non‐doped OLEDs. [ABSTRACT FROM AUTHOR]

A blue fluorescent compound, 9-[4-(4,6-diphenoxy-1,3,5-triazin-2-yl)phenyl]-9 H-carbazole (POTC), the triplet energy level of which reaches 2.76 eV, has been designed and synthesized. POTC is an excellent blue emitter as well as host for green and red phosphors, and therefore, matches the requirements of the host for single-emitting-layer fluorescence and phosphorescence hybrid white organic light-emitting diodes (OLEDs). The blue, green, red, and white devices based on POTC show maximum external quantum efficiencies (EQEs) of 2.4, 22.4, 13.0, and 8.1 %, respectively. Even at a high brightness of 1000 cd m−2, these values maintain EQEs of 2.3, 22.1, 11.1, and 7.0 %, respectively, indicating less than 15 % roll-offs from the maxima. [ABSTRACT FROM AUTHOR]

Flexible organic light‐emitting diodes (OLEDs) are attracting tremendous attention due to their promise as a key element in bendable display and curved lighting applications. However, their performance in terms of efficiency and bendability is limited, since flexible transparent electrodes with superior electrical, optical, and mechanical properties are rare. Here, a multifunctional electrode architecture that is based on flexible plastic, and consists of electrically conductive silver nanowires, a nanopatterned ZnO outcoupling layer, and a hole‐injection polymer layer, is proposed for the actualization of high‐performance flexible OLEDs. The trapped light in the waveguide and substrate modes is effectively released by integrating aperiodic nanostructures into high‐refractive‐index ZnO layers on both sides of the plastic substrate. A maximum external quantum efficiency of 61.7% and a power efficiency of 126.6 lm W−1 are achieved for the white‐emission flexible OLEDs with broadband and angle‐independent outcoupling enhancement. In addition, the proposed approach allows for high‐level mechanical flexibility, retaining over 80% of the initial efficiency after 3000 cycles of repeated bending. [ABSTRACT FROM AUTHOR]

To develop efficient thermally activated delayed fluorescence (TADF) emitters with optimal molecular restrictions for organic light‐emitting diodes (OLEDs), four novel TADF emitters are designed and synthesized: 5′‐(9,9‐dimethylacridin‐10(9H)‐yl)‐[1,1′:3′,1″‐terphenyl]‐2′,4,4″‐tricarbonitrile (oAcTBC), 5′‐(10H‐spiro[acridine‐9,9′‐fluoren]‐10‐yl)‐[1,1′:3′,1″‐terphenyl]‐2′,4,4″‐tricarbonitrile (oSpTBC), 2′‐(9,9‐dimethylacridin‐10(9H)‐yl)‐[1,1′:3′,1″‐terphenyl]‐4,4″,5′‐tricarbonitrile (mAcTBC), and 2′‐(10H‐spiro[acridine‐9,9′‐fluoren]‐10‐yl)‐[1,1′:3′,1″‐terphenyl]‐4,4″,5′‐tricarbonitrile (mSpTBC). The four compounds have similar constituent segments but different molecular restrictions by enhancing either segment rigidity or steric hindrance. The OLEDs using oAcTBC, oSpTBC, mAcTBC, and mSpTBC as the emitter exhibit maximum external quantum efficiencies of 20.9%, 26.8%, 19.2%, and 18.9%, respectively, consistent with their photoluminescence quantum yield values of 83.88%, 93.24%, 76.64%, and 65.02%. The best performance is successfully realized by oSpTBC with the optimal molecular restriction. This work suggests that appropriately enhancing the molecular restrictions with more rigid constituent segments is an optimal approach to improve the efficiencies of TADF emitters. Four thermally activated delayed fluorescence (TADF) emitters with similar constituent segments but different molecular restrictions are developed. The 5′‐(10H‐spiro[acridine‐9,9′‐fluoren]‐10‐yl)‐[1,1′:3′,1″‐terphenyl]‐2′,4,4″‐tricarbonitrile (oSpTBC)‐based organic light‐emitting diodes (OLEDs) exhibit highest efficiencies with a maximum external quantum efficiency (EQE) of 26.8%. These results suggest that appropriately enhancing the molecular restrictions with more rigid constituent segments is an optimal approach to improve the efficiencies of TADF emitters. [ABSTRACT FROM AUTHOR]

Multi-resonance (MR) thermally activated delayed fluorescence (TADF) materials with planar rigidity show great potential as emitters in organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yields and narrowband emission. However, their strong intermolecular interaction trends usually result in redshifted and broadened emission spectra as well as low device efficiencies due to the aggregation-caused quenching (ACQ) effect. In this paper, a bulky spirobifluorene unit was appended onto an asymmetric carbazole/diphenylamine-embedded MR skeleton to relieve such trends, thus affording a new MR-TADF blue emitter, BNSF-1. Introducing spirobifluorene significantly relieves the intermolecular interaction trends of MR backbones without affecting their original photophysical properties. The corresponding sensitizer-free OLED devices based on BNSF-1 exhibit narrowband sky-blue electroluminescence peaking at 475 nm with a full width at half-maximum of 25 nm, as well as a maximum external quantum efficiency of 25.9 %. More importantly, BNSF-1 exhibited negligible spectral broadening and ACQ trends as the doping ratio increased. Our work provides a feasible method for constructing doping concentration-insensitive MR-TADF emitters. [Display omitted] • A novel multi-resonance TADF emitter with spirobifluorene unit is developed. • The emitter exhibits blue emission at 475 nm with a small FWHM of 25 nm. • Maximum external quantum efficiency of 25.9 % and PLQY of 92.6 % are realized. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two multiple resonance derivatives with heavy atom-containing chains are developed. • A new heavy atom effect involvement method for enhancing RISC of MR emitters. • TCzBN-S based evaporated OLEDs afford a low roll-off of 44% at 1000 cd m−2. • Both emitters are feasible for solution-process OLEDs with high performance. Multiple resonance (MR)-based thermally activated delayed fluorescence (TADF) emitters are promising candidates for ultra-high definition (UHD) organic light-emitting diodes (OLEDs). However, the device performances of MR-TADF emitters are usually encumbered with their slow reverse intersystem crossing (RISC) rates (k RISC s). Recently, applying heavy atom effect to MR emitters has been proved to be a plausible solution for enhancing their k RISC and improving TADF properties. Nevertheless, to date, heavy atoms have all been directly fused in MR frameworks, leading to limitations in molecular design and additional structure relaxation from heavy atoms. Herein, we incorporate heavy atom effect via facilely hanging heavy atom-containing chains onto a MR framework and thus synthesize two MR emitters (sulfur ether group for TCzBN-S and sulfone group for TCzBN-SO). An enhanced k RISC of 1.40 × 105 s−1 is reached for TCzBN-S due to sufficient natural transition orbital (NTO) contributions from the heavy atom, which is absent for TCzBN-SO, with a relatively slow k RISC of 5.6 × 104 s−1. Consequently, OLEDs employing TCzBN-S as emitter achieve a maximum external quantum efficiency (EQE) of 30.0% and an alleviated efficiency roll-off of 44% at 1000 cd m−2. In contrast, OLEDs based on TCzBN-SO achieve a maximum EQE of 33.0% but a more severe efficiency roll-off 1000 of 65%. Moreover, solution-process OLEDs based on TCzBN-S and TCzBN-SO are also fabricated and achieved high EQEs of 23.3% and 25.5%, respectively, demonstrating that peripheral flexible and hanging heavy atom chains are also beneficial to solution processing. Our work not only extends heavy atom involving modes in MR emitters, which are important for further developing MR derivatives by using the heavy atom effect, but also confirms that such MR derivatives with hanging chains are applicable to both vacuum-evaporation and solution-process OLEDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developing red TADF emitters by simultaneously employing polycyclic large-conjugation donor and acceptor units. • The first example of delicate management of 3LE D and 3LE A for constructing a high-performance red TADF emitter. • DBBPZ-IDPZ delivers fast k RISC and high PLQY of 98.1% thanks to the joint contribution of 3LE D and 3LE A. • DBBPZ-IDPZ based OLED affords an improved EQE of 26.0 %, peaking at 628 nm. Accelerating reverse intersystem crossing (RISC) rates of red thermally activated delayed fluorescence (TADF) emitters is crucial yet remains ongoing challenges. Herein, we disclose an ingenious molecular design to dramatically boost such an up-conversion process by leveraging effective participation of localized excited triplet states from both donor and acceptor segments (3LE D and 3LE A). Inspiringly, energy level alignment with 3LE A -3LE D close to the charge-transfer singlet and triplet (1CT and 3CT) states are obtained in the case of DBBPZ-IDPZ, by simultaneously employing polycyclic large-conjugation donor and acceptor units. Due to the joint contribution of 3LE D and 3LE A , DBBPZ-IDPZ shows 15.7 folds accelerated RISC rate and delivers a higher photoluminescence quantum yield of 98.1 % relative to the control molecule (36.7 %). Eventually, the red OLED based on DBBPZ-IDPZ presents a significantly improved external quantum efficiency of 26.0 % with an emission maximum at 628 nm, which is approximately triple that of the control device (8.9 %). This is the first example of a delicate management of 3LE D and 3LE A to simultaneously participate in RISC process for developing highly efficient red TADF emitters. Our work provides new insights into the molecular design tactic of high-performance red TADF OLEDs. [ABSTRACT FROM AUTHOR]

To develop high-performance solution-processed thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) based on exciplex emitters, a novel strategy was present to develop ternary polymer-based exciplex emitter by introducing the third small-molecule constituent material into binary polymer-based exciplex in this work. Compared with common binary polymer-based exciplex emitters, such ternary polymer-based exciplex emitters could not only enhance up-conversion of nonradiative triplet excitons and realize higher exciton utilization, but also maintain the superiorities of polymers in solution processing, like excellent film-forming ability and thermal stability. Based on our strategy, a highly efficient ternary polymer-based exciplex PVK:PO-T2T:mCP was developed. As expected, PVK:PO-T2T:mCP successfully realizes much higher photoluminescence quantum yield of 82.0% and rate constant of RISC process of 2.62 × 105 than PVK:PO-T2T. In the solution-processed OLEDs, interfacial PVK:PO-T2T:mCP exhibits a record-high maximum external quantum efficiency of 21.9% for polymer-based exciplexes, demonstrating the superiority of our strategy for further development of solution-processed TADF-OLEDs. Image 1 • Solution-processed TADF-OLEDs were successfully developed by using ternary polymer-based exciplex PVK:PO-T2T:mCP as the emitters. • Ternary exciplex PVK:PO-T2T:mCP exhibits much higher Φ PL (82.0%), k R ISC (2.62 × 105) and lower k n r T (2.07 × 104) than PVK:PO-T2T. • This work is the first report with an over 20% EQE for the OLEDs using polymer-based exciplexes as the emitters. [ABSTRACT FROM AUTHOR]