The development of efficient metal‐free organic emitters with thermally activated delayed fluorescence (TADF) properties for deep‐blue emission is still challenging. A new family of deep‐blue TADF ...emitters based on a donor–acceptor architecture has been developed. The electronic interaction between donor and acceptor plays a key role in the TADF mechanism. Deep‐blue OLEDs fabricated with these TADF emitters achieved high external quantum efficiencies over 19.2 % with CIE coordinates of (0.148, 0.098).
Deep blue emission: An internal quantum efficiency (IQE) of almost 100 % was achieved in organic light‐emitting diodes by a rational molecular design strategy. The organic light‐emitting diodes showed deep‐blue thermally activated delayed fluorescence.
By simple modification of the functional groups on the donor unit, the thermally activated delayed fluorescence (TADF) properties of emitters can easily be manipulated. A series of deep blue to blue ...emissive TADF derivatives is developed, capable of deep‐blue emissions from 403 to 460 nm in toluene. Deep‐blue organic light‐emitting diodes (OLEDs) based on this series of TADF emitters are fabricated, resulting in an electroluminescence peak at 428 nm and a high external quantum efficiency of up to 10.3%. One deep‐blue OLED has achieved the commission internationale de l'eclairage (CIE) coordinates of (0.156, 0.063), which is among the best reported TADF performances for deep‐blue OLEDs with CIEy < 0.07.
A series of deep‐blue to blue emissive TADF derivatives is developed, by which deep‐blue emissions from 403 to 460 nm in toluene are achieved. Deep‐blue OLEDs based on this series of TADF emitters are fabricated, exhibiting an electroluminescence peak at 428 nm and a high external quantum efficiency of up to 10.3%.
A family of organic emitters with a donor–σ–acceptor (D‐σ‐A) motif is presented. Owing to the weakly coupled D‐σ‐A intramolecular charge‐transfer state, a transition from the localized excited ...triplet state (3LE) and charge‐transfer triplet state (3CT) to the charge‐transfer singlet state (1CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200–400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D‐σ‐A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.
Avoid long delays: A novel molecular design for thermally activated delayed fluorescence (TADF) emitters based on a donor–σ–acceptor motif led to short TADF decay lifetimes of less than 400 ns. Since shorter delayed lifetimes in TADF emitters are highly beneficial for device performance, this design strategy is expected to provide an effective approach to advanced TADF materials.
This study investigates the effect of state ownership on Chinese firms' foreign direct investment (FDI) ownership decisions. It adopts a political perspective to extend the application of ...institutional theory in international business research. Specifically, it examines firms' heterogeneous responses to external institutional processes during foreign market entry, while taking into consideration the political affiliation of firms with the external institutions. We argue that state ownership creates the political affiliation of a firm with its home-country government, which increases the firm's resource dependence on homecountry institutions, while at the same time influencing its image as perceived by host-country institutional constituents. Such resource dependence and political perception increase firms' tendency to conform to, rather than resist, isomorphic institutional pressures. We tested our hypotheses using primary data for 132 FDI entries made by Chinese firms during 2000–2006, and we found that the effects of home regulatory, host regulatory and host normative pressures on a firm to choose a joint ownership structure were stronger when the share of equity held by state entities in the firm was high.
Defocus is an important factor that causes image quality degradation of optoelectronic tracking equipment in the shooting range. In this paper, an improved blind/referenceless image spatial quality ...evaluator (BRISQUE) algorithm is formulated by using the image characteristic extraction technology to obtain a characteristic vector (CV). The CV consists of 36 characteristic values that can effectively reflect the defocusing condition of the corresponding image. The image is evaluated and scored subjectively by the human eyes. The subjective evaluation scores and CVs constitute a set of training data samples for the defocusing evaluation model. An image database that contains sufficiently many training samples is constructed. The training model is trained to obtain the support vector machine (SVM) model by using the regression function of the SVM. In the experiments, the BRISQUE algorithm is used to obtain the image feature vector. The method of establishing the image definition evaluation model via SVM is feasible and yields higher subjective and objective consistency.
As heavy metal ions severely harm human health, it is important to develop simple, sensitive and accurate methods for their detection in environment and food. Electrochemical detection featured with ...short analytical time, low power cost, high sensitivity and easy adaptability for in-situ measurement is one of the most developed methods. This review introduces briefly the recent achievements in electrochemical sensing of heavy metal ions with inorganic, organic and bio-materials modified electrodes. In particular, the unique properties of inorganic nanomaterials, organic small molecules or their polymers, enzymes and nucleic acids for detection of heavy metal ions are highlighted. By employing some representative examples, the design and sensing mechanisms of these electrodes are discussed.
•Recent achievements in electrochemical sensing of heavy metal ions are introduced.•Inorganic, organic and bio-materials modified electrodes are highlighted.•The design of sensors for heavy metal ions and their sensing mechanisms are discussed.•Sensing mechanisms for indirect detection of heavy metal ions are summarized.
In this work, two novel thermally activated delayed fluorescence (TADF) emitters, 2tDMG and 3tDMG, are synthesized for high‐efficiency organic light‐emitting diodes (OLEDs), The two emitters have a ...tilted face‐to‐face alignment of donor (D)/acceptor (A) units presenting intramolecular noncovalent interactions. The two TADF materials are deposited either by an evaporation‐process or by a solution‐process, both of them leading to high OLED performance. 2tDMG used as the emitter in evaporation‐processed OLEDs achieves a high external quantum efficiency (EQE) of 30.8% with a very flat efficiency roll‐off of 7% at 1000 cd m−2. The solution‐processed OLEDs also display an interesting EQE of 16.2%. 3tDMG shows improved solubility and solution processability as compared to 2tDMG, and thus a high EQE of 20.2% in solution‐processed OLEDs is recorded. The corresponding evaporation‐processed OLEDs also reach a reasonably high EQE of 26.3%. Encouragingly, this work provides a novel strategy to address the imperious demands for OLEDs with high EQE and low roll‐off.
A thermally activated delayed fluorescence emitter, 2tDMG, is designed and synthesized based on the donor (D)/acceptor (A) spatially intramolecular noncovalent interaction. The D/A units are connected via a rigid linker, thereby confining them into a close‐packed coplanar configuration for small singlet–triplet splitting energy. 2tDMG achieves a high external quantum efficiency of 30.8% with a low efficiency roll‐off in evaporation‐processed organic light‐emitting diodes (OLEDs).
Much effort has been devoted to developing highly efficient organic light‐emitting diodes (OLEDs) that function through phosphorescence or thermally activated delayed fluorescence (TADF). However, ...efficient host materials for blue TADF and phosphorescent guest emitters are limited because of their requirement of high triplet energy levels. Herein, we report the rigid acceptor unit benzimidazobenzothiazole (BID‐BT), which is suitable for use in bipolar hosts in blue OLEDs. The designed host materials, based on BID‐BT, possess high triplet energy and bipolar carrier transport ability. Both blue TADF and phosphorescent OLEDs containing BID‐BT‐based derivatives exhibit external quantum efficiencies as high as 20 %, indicating that these hosts allow efficient triplet exciton confinement appropriate for blue TADF and phosphorescent guest emitters.
Gotta catch them all: Over 20 % external quantum efficiencies were achieved in both blue thermally activated delayed fluorescence (TADF) and phosphorescent organic light‐emitting diodes (OLEDs) using benzimidazobenzothiazole bipolar host materials.
Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called ...thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.
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