Intramolecular exciplex featuring a bis-sp3 C-locked acceptor-donor-acceptor sandwich.

Intramolecular exciplex systems featuring thermally activated delayed fluorescence (TADF) have garnered significant attention in the realm of organic light-emitting diodes (OLEDs). Nonetheless, the occurrence of organic sandwich intramolecular exciplexes remains rare due to structural limitations and synthetic challenges. Herein, we present a novel rigid acceptor-donor-acceptor (A-D-A) sandwich complex, dSFQP, characterized by two sp3 C-locking moieties. This compound exhibits TADF characteristics facilitated by a multiple through-space charge-transfer process. X-ray crystallographic analysis confirms the distinctive sandwich configuration. The parallel spatial arrangement and minimized A-D-A configuration enhance electronic interactions, resulting in a high photoluminescence quantum yield, rapid reverse intersystem crossing rate, and sluggish nonradiative decay rate. OLEDs employing dSFQP as the dopant achieve a maximum external quantum efficiency (EQE) of 28.5% with a low efficiency roll-off of merely 2.8% at 1000 cd m-2. Even at a high brightness of 10 000 cd m-2, the EQE remains notably high at 17.5%. Our current results provide an effective way to further innovate the design of new organic charge-transfer complexes.

Rational Multidimensional Shielded Multiple Resonance Emitter Suppresses Concentration Quenching and Spectral Broadening for Solution-Processed Organic Light-Emitting Diodes.

Thermally activated delayed fluorescence (TADF) emitters based on multiple resonance (MR) effects are promising for high-definition organic light-emitting diodes (OLEDs) with narrowband emission and high efficiency. However, they still face the challenges of aggregation-caused quenching (ACQ) and spectral broadening. Solution-processable MR-TADF emitters with an external quantum efficiency (EQE) of >20% and a full width at half-maximum (fwhm) of <30 nm have rarely been reported. To construct ACQ-resistant emitters without sacrificing color purity, the aggregation-induced MR-TADF material 6TBN with a rigid B,N-containing polycyclic aromatic hydrocarbon core and four carbazole substituents as well as 12 tert-butyl groups on the periphery is designed. The multidimensional shielded effect largely limits the ACQ, intermolecular interactions, and spectral broadening. Consequently, solution-processed OLEDs based on 6TBN exhibit a maximum EQE of 23.0% and high color purity with a fwhm of 25 nm. Furthermore, the nondoped device achieves a high efficiency (12.3%) and merely a slight widening of the fwhm to 27 nm. This work provides a feasible strategy to achieve MR-TADF materials with resistance to concentration quenching and high color purity.

A Dislocated Twin-Locking Acceptor-Donor-Acceptor Configuration for Efficient Delayed Fluorescence with Multiple Through-Space Charge Transfer.

Organic materials featuring intramolecular through-space charge transfer (TSCT) excited states are advantageous for efficient thermally activated delayed fluorescence (TADF), although the realization of multiple TSCT systems remains challenging. Herein, a rigid molecule with a three-dimensional dislocated sandwich acceptor-donor-acceptor configuration has been developed by a linking biphenazine (2PXZ) donor and 2,4,6-triphenyl-1,3,5-triazine (TRZ) acceptor through the twin-locking of two spiro-fluorene bridges. The twin-locking construction with multiple TSCT effects suppresses the intramolecular rotations of various segments in 2PXZ-2TRZ, leading to a small singlet-triplet energy difference, a fast reverse intersystem crossing process, and high photoluminescence quantum yield. This material simultaneously possesses the capabilities of TADF and aggregation-induced emission. The device employing 2PXZ-2TRZ as a dopant displays an optimal external quantum efficiency of 27.1 % and a low efficiency roll-off.

Interfacial "Anchoring Effect" Enables Efficient Large-Area Sky-Blue Perovskite Light-Emitting Diodes.

While tremendous progress has recently been made in perovskite light-emitting diodes (PeLEDs), large-area blue devices feature inferior performance due to uneven morphologies and vast defects in the solution-processed perovskite films. To alleviate these issues, a facile and reliable interface engineering scheme is reported for manipulating the crystallization of perovskite films enabled by a multifunctional molecule 2-amino-1,3-propanediol (APDO)-triggered "anchoring effect" at the grain-growth interface. Sky-blue perovskite films with large-area uniformity and low trap states are obtained, showing the distinctly improved radiative recombination and hole-transport capability. Based on the APDO-induced interface engineering, synergistical boost in device performance is achieved for large-area sky-blue PeLED (measuring at 100 mm2 ) with a peak external quantum efficiency (EQE) of 9.2% and a highly prolonged operational lifetime. A decent EQE up to 6.1% is demonstrated for the largest sky-blue device emitting at 400 mm2 .

Rational Interface Engineering for Efficient Flexible Perovskite Light-Emitting Diodes.

Although perovskite light-emitting diodes (PeLEDs) are promising for next-generation displays and lighting, their efficiency is still considerably below that of conventional inorganic and organic counterparts. Significant efforts in various aspects of the electroluminescence process are required to achieve high-performance PeLEDs. Here, we present an improved flexible PeLED structure based on the rational interface engineering for energy-efficient photon generation and enhanced light outcoupling. The interface-stimulated crystallization and defect passivation of the perovskite emitter are synergistically realized by tuning the underlying interlayer, leading to the suppression of trap-mediated nonradiative recombination losses. Besides approaching highly emissive perovskite layers, the outcoupling of trapped light is also enhanced by combining the silver nanowires-based electrode with quasi-random nanopatterns on flexible plastic substrate. Upon the collective optimization of the device structure, a record external quantum efficiency of 24.5% is achieved for flexible PeLEDs based on green-emitting CsPbBr3 perovskite.

Management of Delayed Fluorophor-Sensitized Exciton Harvesting for Stable and Efficient All-Fluorescent White Organic Light-Emitting Diodes.

White organic light-emitting diodes (WOLEDs) using thermally activated delayed fluorescence (TADF)-based single emissive layer (SEL) have attracted enormous attention because of their simple device structure and full exciton utilization potential for high efficiency. However, WOLEDs made of an all-TADF SEL usually exhibit serious efficiency roll-off and poor color stability due to serious exciton-annihilation and unbalanced radiative decays of different TADF emitters. Herein, a new strategy is proposed to manipulate the TADF-sensitized fluorescence process by combining dual-host systems of high triplet energy with a conventional fluorescent emitter of complementary color. The multiple energy-funneling paths are modulated and short-range Dexter energy transfer is largely suppressed due to the steric effect of peripheral tert-butyl group in the blue TADF sensitizer. The resulting all-fluorescent WOLEDs achieve an unprecedentedly high external quantum efficiency of 21.8% with balanced white emission of Commission Internationale de l'Eclairage coordinate of (0.292, 0.343), accompanied with good color stability, reduced efficiency roll-off, and prolonged operational lifetime. These findings demonstrate the validity of this strategy for precisely allocating the exciton harvesting in SEL WOLEDs.

High-Performance Nondoped Blue Delayed Fluorescence Organic Light-Emitting Diodes Featuring Low Driving Voltage and High Brightness.

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).

Rational Molecular Design of Dibenzo[a,c]phenazine-Based Thermally Activated Delayed Fluorescence Emitters for Orange-Red OLEDs with EQE up to 22.0.

The design and synthesis of highly efficient thermally activated delayed fluorescence (TADF) emitters with an electroluminescence wavelength beyond 600 nm remains a great challenge for organic light-emitting diodes (OLEDs). To solve this issue, three TADF molecules, xDMAC-BP (x = 1, 2, 3), are developed in combination with the rigid planar dibenzo[a,c]phenazine (BP) acceptor core and different numbers of 9,9-dimethylacridan (DMAC) donors. All these emitters possess stable internal charge transfer and a large dihedral angle between the donors and planar BP core. The emission wavelength can be regulated from 541 to 605 nm by increasing the number of the donor DMAC units because of the controllable tuning of the intramolecular charge transfer effect and the molecular geometrical structure. The photoluminescence quantum yields of these emitters are improved from 42 to 89% with the increase in the number of DMAC units. The orange-red OLEDs employing the xDMAC-BP emitters exhibit maximum external quantum efficiency (EQE) of 22.0% at 606 nm, which is the highest EQE of the previously reported TADF OLEDs exceeding 600 nm.

Two novel blue phosphorescent host materials containing phenothiazine-5,5-dioxide structure derivatives.

Two novel D-A bipolar blue phosphorescent host materials based on phenothiazine-5,5-dioxide: 3-(9H-carbazol-9-yl)-10-ethyl-10H-phenothiazine-5,5-dioxide (CEPDO) and 10-butyl-3-(9H-carbazol-9-yl)-10H-phenothiazine-5,5-dioxide (CBPDO) were synthesized and characterized. The photophysical, electrochemical and thermal properties were systematically investigated. CEPDO and CBPDO not only have a high triplet energy but also show a bipolar behavior. Moreover, their fluorescence emission peaks are in the blue fluorescence region at 408 nm and the fluorescence quantum efficiency (Φ) of CEPDO and CBPDO were 62.5% and 59.7%, respectively. Both CEPDO and CBPDO showed very high thermal stability with decomposition temperatures (Td) of 409 and 396 °C as well as suitable HOMO and LUMO energy levels. This preferable performance suggests that CEPDO and CBPDO are alternative bipolar host materials for the PhOLEDs.