Organic push-pull systems featuring through-space charge transfer (TSCT) excited states have been disclosed to be capable of exhibiting thermally activated delayed fluorescence (TADF), but to realize high-efficiency long-wavelength emission still remains a challenge. Herein, we report a series of strongly emissive orange-red and red TSCT-TADF emitters having (quasi)planar and rigid donor and acceptor segments which are placed in close proximity and orientated in a cofacial manner. Emission maxima (λem) of 594−599 nm with photoluminescence quantum yields (PLQYs) of up to 91% and delayed fluorescence lifetimes of down to 4.9 μs have been achieved for new acceptor-donor-acceptor (A-D-A) molecules in doped thin films. The presence of multiple acceptors and the strong intramolecular π-stacking interactions have been unveiled to be crucial for the efficient low-energy TSCT-TADF emissions. Organic light-emitting diodes (OLEDs) based on the new A-D-A emitters demonstrated electroluminescence with maximum external quantum efficiencies (EQEs) of up to 23.2% for the red TSCT-TADF emitters. An EQE of 18.9% at the brightness of 1000 cd m-2 represents one of the highest values for red TADF OLEDs. This work demonstrates a modular approach for developing high-performance red TADF emitters through engineering through-space interactions, and it may also provide implications to the design of TADF emitter with other colours.
The harnessing of heavy atom effect of chalcogen elements offers a way for boosting the thermally activated delayed fluorescence (TADF) of purely organic luminescent materials that can harvest triplet excitons. However, the conformational and electronic variations induced by the heavy and large atoms may also have adverse effects on the TADF properties. Herein, the design, synthesis, and structures of a new type of through‐space charge transfer (TSCT) emitters containing benzothiazino[2,3,4‐kl]phenothiazine (DPTZ) as the donor unit are reported. The influences of S atoms on the emission properties have been systematically investigated by means of theoretical simulations, electrochemical and spectroscopic studies. Although the presence of π‐stacking interactions and calculated spin‐orbit coupling (SOC) values are beneficial for TSCT‐TADF properties, the triplet TSCT states are uplifted to above the locally excited (LE) state of the acceptor moieties. As a result, the new emitters display longer delayed fluorescence lifetimes (τDF) of 255.0–114.3 μs and lower PLQYs of 45–61 % in comparison with the O‐containing congeners (τDF=26.9–6.8 μs; PLQYs=74–71 %). This work highlights that a full consideration of various effects is essential when making use of heavy chalcogen atoms for the design of TADF emitters.
For the disadvantage of the low flux's observational accuracy of induction motor direct torque control system when it runs in a low velocity, the full order flux observer is used to achieve the stator flux observation.Based on the analysis of four full order flux observer pole placement methods,The impact on observational accuracy and convergence rate was researched with different parameters of the Gain Matrix in the single degree of freedom pole placement method.The simulation results show that to ensure the stability of the system,the impacts on the flux observation were Effectively inhibited when Motor's stator and rotor resistance parameters change through increasing parameter of the Gain Matrix,and the flux observer's robustness was improved.
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