Search

Reasonable energy level alignment of molecules is conducive to constructing high‐performance blue emitter. Pyrene is a common building unit in blue emitters with a big energy gap between S1 and T1 (ΔES1‐T1) and small ΔES1‐Tn (n = 2‐3). By introducing donor and acceptor groups in pyrene, the high‐lying triplet excitons are utilized through reverse intersystem crossing (RISC) channel in obtained blue "hot exciton" emitter CPPCN. Herein, through changing the donor linking type to ortho‐substituted, the obtained derivatives o‐CPPCN exhibited deeper blue emission (λmax = 448 nm) and a higher krisc (3.1×108 s−1). The non‐doped device based on o‐CPPCN demonstrates a maximum external quantum efficiency (EQEmax) of 10.3% with a CIEy of 0.11, along with an exciton utilization of 55%. Photophysical measurements indicate the performance difference between the CPPCN and o‐CPPCN originates from the energy level alignment difference. Compared with CPPCN (0.26 eV), the ΔES1‐T2 of o‐CPPCN has been reduced to 0.10 eV, proving the smaller gap between T2 and S1 state can promote the RISC process. Hence, o‐CPPCN can be employed as the host to prepare "hot exciton" sensitized blue OLED due to its wide band gap and high krisc. The corresponding EQEmax of the doped device can be further improved to 11.8%. [ABSTRACT FROM AUTHOR]

Robust organic luminescent materials radiating deep‐red/near‐infrared (DR/NIR) light are highly desired in organic light‐emitting diodes (OLEDs). However, most reported DR/NIR materials show only moderate electroluminescence (EL) efficiencies accompanied by rock‐ribbed efficiency roll‐offs, which immensely limit their practical use in OLEDs. In this work, two tailor‐made NIR luminescent materials with thermally activated delayed fluorescence (TADF) property are developed based on rigid and strong electron‐accepting core of 2,7‐bis(4‐cyanophenyl)dibenzo[a,c]phenazine‐11,12‐dicarbonitrile and electron donors of triphenylamine or N,N‐di([1,1′‐biphenyl]‐4‐yl)phenylamine. They exhibit high photoluminescence quantum yields, fast reverse intersystem crossing processes and large horizontal dipole ratios. Their nondoped OLEDs show NIR lights with maximum external quantum efficiencies (ηext,maxS) of 0.59% at 856 nm and 1.14% at 850 nm. And their doped OLEDs radiate DR to NIR lights (646–737 nm) and attain superb ηext,maxs of up to 30.3% at 646 nm with small efficiency roll‐offs. The state‐of‐the‐art EL performances of both NIR TADF materials demonstrate their high potential as emitters in OLEDs and the insights gained in this work will enlighten the further development of efficient NIR luminescent materials. [ABSTRACT FROM AUTHOR]

High‐quality near‐ultraviolet/deep‐blue organic emitters are urgently needed but still rare. Here, three V‐shape donor‐acceptor‐donor (D‐A‐D) emitters based on pyrazine cores, namely, VDMP‐PhCz, VDMP‐36PhCz, and VDMP‐TPA, are designed and synthesized. Their doped devices using a high‐polar host show remarkable electroluminescence (EL) performances with maximum external quantum efficiency (EQE) values up to 7.37%, 7.55%, and 9.03%, and corresponding CIE coordinates of (0.160,0.040), (0.161,0.039), and (0.149,0.072), respectively. Supported by theoretical calculations and experimental results, the high EL performances of these emitters are achieved by their planarized intramolecular charge transfer (PLICT) features, high triplet‐excitons utilization from "hot exciton" channels, and high horizontal dipole orientations. Furthermore, these PLICT‐based emitters can also function as efficient hosts for green or yellow multi‐resonance (MR) narrowband emissive guests, providing high EQEs of over 32% with alleviated efficiency roll‐offs. [ABSTRACT FROM AUTHOR]

The outstanding performance of halide perovskite makes it one of the champion materials for applications in optoelectronic devices. However, the stability of perovskites limits their practical applications. Among all the factors influencing the stability of perovskites, defects are one of the key factors. Till now, many chemical methods have been proposed to passivate defects. Nevertheless, there is still a lack of in situ passivation methods without the change of the composition of perovskites. Here, it is found that the external electric field can passivate the defects in FPEA2PbI4 (FPEAI = 2‐(4‐Fluorophenyl)ethylamine Hydroiodide) film in a capacitive device at 78 K, and the PL intensity can be enhanced greatly. A "charge‐soaking effect" can be observed, that is PL intensity continues to increase for a long time after removing the electric field. Besides the emission peak from free exciton, two other peaks at the lower energy side from defect‐bound excitons are observed. They are more susceptible to the external electric field than the free exciton. This work will deepen the understanding of exciton behavior and the interaction of electric field with excitons in two–dimensional (2D) hybrid perovskites for efficient light–emitting diodes (LEDs) and electrically pumped lasers. It provides a new in situ passivation method of perovskites for practical applications. [ABSTRACT FROM AUTHOR]

Efficient blue organic luminescent materials are highly desired for full‐color displays and white lighting based on the organic light‐emitting diode (OLED) technique, but the exploration of robust blue emitters remains challenging. In this work, a series of efficient blue thermally activated delayed fluorescence materials comprised of a benzonitrile acceptor, pyridine bridge, and carbazole‐based donors is designed and synthesized. Intramolecular hydrogen bonds are formed in these molecules, which improve molecular planarity and rigidity. These molecules exhibit excellent thermal stability, high photoluminescence quantum yields, and large horizontal dipole ratios. Highly efficient non‐doped and doped OLEDs are fabricated using these molecules as emitters, providing deep‐blue to sky‐blue lights with outstanding maximum external quantum efficiencies and good operational device lifetime. These results indicate that building intramolecular hydrogen bonds can be an effective strategy for the construction of efficient and robust blue emitters for OLED applications. [ABSTRACT FROM AUTHOR]

"Hot exciton" molecules that allow the transition of excitons from a high‐lying triplet state (Tn, n≥ 2) to singlet states (Sm, m≥1) by a reverse intersystem crossing (hRISC) process have become an effective strategy to achieve high efficiency fluorescence organic light emitting diodes (OLEDs). However, the understanding of the dynamic behavior of the "hot exciton" process is still very lacking. Herein, the exciton dynamics of an aggregation‐induced emission (AIE) molecule TPA‐An‐mPhCz with the "hot exciton" property are deeply investigated, and the proportion between hRISC and internal inversion (IC) of excitons on Tn is successfully quantified by in situ transient electroluminescent measurements and theoretical calculation. It is found that the IC process increases severe energy loss of Tn excitons. By introducing a triplet–triplet annihilation up‐conversion layer in the emissive layer to efficiently recapture the IC excitons and further doping a blue fluorescent emitter in the TPA‐An‐mPhCz layer to achieve high photoluminescence quantum yield (PLQY), the resulting OLED achieves a maximum external quantum efficiency of 12.5% with negligible efficiency roll‐off. More impressively, the operational lifetime LT75 (lifetime to 75% of the initial luminance) of the device with efficient triplets utilization performs a remarkable 116 h under 1000 cd m−2. This work provides the fundamentals for the design of hot exciton materials with efficient exciton utilization to develop efficient blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

Aggregation‐induced emission (AIE) materials are attractive for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs) owing to the "hot exciton" process by reverse intersystem crossing (hRISC) and high photoluminescence quantum yields (PLQY). However, the internal conversion (IC) from the high‐lying triplet excitation states (Tn, n≥2) to the lower excited triplet state (Tn‐1) is inevitable, resulting in severe exciton losses. Herein, an effective device structure is designed that reuses the lost triplet excitons caused by IC and realizes the breakthrough in the efficiency of blue fluorescence OLEDs based on AIE molecule as an emitter. The maximum external quantum efficiency reached as high as 14.8% and is kept at 14.4% at the luminance of 1000 cd m−2. In the designed device, a triplet–triplet annihilation (TTA) up‐conversion material 1‐[2,5‐dimethyl‐4‐(1‐pyrenyl)phenyl]pyrene (DMPPP) is introduced into the AIE emitter as a triplet sensitizer to receive the lost triplet excitons, and a thin TTA up‐conversion layer 9‐[4‐(10‐phenyl‐9‐anthryl)phenyl]‐9H‐carbazole (CzPA) is introduced in the middle of the doped layer to form the emissive layer (EML). It is found that the hRISC process of iTPB‐2AC greatly enhances the utilization efficiency of TTA intermediate state ([TT]*) excitons on CzPA to iTPB‐2AC so that the utilization of the lost excitons is maximized. This work establishes physical insights into the AIE emission materials and device fabrication of high‐efficiency blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

High‐performance deep‐blue fluorescent materials matching the required Commission Internationale de l'Eclairage y coordinate value (CIEy) of < 0.08 are much‐needed in organic light‐emitting diodes (OLEDs) for realizing the perfect application of full‐color displays. However, deep‐blue fluorophors commonly show unsatisfactory performance due to the intrinsic large bandgap characteristic. Here, the deep‐blue nondoped OLED with the good CIE coordinates of (0.15, 0.07) and external quantum efficiency (EQE) of ≈9% is achieved based on a multifunctional and efficient anthracene‐based fluorophor (2M‐ph‐3CzAnBzt). Using it as a host, the sky‐blue fluorescent OLED realizes the maximum EQE of 9.50%, and keeps as high as 9.27% and 8.56% at 1000 and 5000 cd m−2. More surprisingly, high‐performance hybrid white OLEDs (WOLEDs) with good color stability and low roll‐off are achieved by using it as the blue emitter. Two‐color WOLED shows the forward‐viewing efficiencies of 20.46%, and 76.80 lm W−1. The three‐color WOLED emitting a candlelight with the color rendering index of ≥ 82 realizes the maximum EQE of 21.49% and remains 20.80% at 1000 cd m−2. Such superior electroluminescence performance achieved in these OLEDs ranks among the highest values based on deep‐blue fluorophors with CIEy < 0.08. [ABSTRACT FROM AUTHOR]

Bioimaging guided photothermal therapy possesses great promise for lesion diagnosis and effective treatment. However, distinguishing lesion from normal tissues for precise cancer therapy remains a great challenge. Herein, a stimulation‐responsive assembled Ag2S vesicle (Ag2S Ve) is proposed by self‐assembly of Ag2S quantum dots (QDs) coated with pH‐sensitive copolymer thiolated polystyrene‐co‐poly(4‐vinylpyridine). The Ag2S Ve shows significant absorption enhancement in the near‐infrared (NIR) region and strong fluorescence inhibition in the second near infrared (NIR‐II) region. Triggered by the acidic environment, the release of Ag2S QDs promptly mediates the quenched NIR‐II fluorescence from "off" to "on." In vivo studies reveal that the theranostic Ag2S Ve can be specifically activated in acidic tumor tissues, whereas it exhibits nonfunctional in normal tissues. Larger sizes endow vesicles a higher tumor accumulation efficiency and controllable disassembly shows illuminating characteristics toward lesion tissues, which provides an innovative therapeutic strategy for activated NIR‐II fluorescence imaging guided cancer therapy. [ABSTRACT FROM AUTHOR]