Organic semiconductors can be designed and constructed in π‐stacked structures instead of the conventional π‐conjugated structures. Through‐space interaction (TSI) occurs in π‐stacked optoelectronic ...materials. Thus, unlike electronic coupling along the conjugated chain, the functional groups can stack closely to facilitate spatial electron communication. Using π‐stacked motifs, chemists and materials scientists can find new ways for constructing materials with aggregation‐induced emission (AIE), thermally activated delayed fluorescence (TADF), circularly polarized luminescence (CPL), and room‐temperature phosphorescence (RTP), as well as enhanced molecular conductance. Organic optoelectronic devices based on π‐stacked molecules have exhibited very promising performance, with some of them exceeding π‐conjugated analogues. Recently, reports on various organic π‐stacked structures have grown rapidly, prompting this review. Representative molecular scaffolds and newly developed π‐stacked systems could stimulate more attention on through‐space charge transfer the well‐known through‐bond charge transfer. Finally, the opportunities and challenges for utilizing and improving particular materials are discussed. The previous achievements and upcoming prospects may provide new insights into the theory, materials, and devices in the field of organic semiconductors.
Unlike traditional covalent bond‐connected conjugated molecules, π‐stacked small molecules have special advantages in organic semiconductors. This review mainly focuses on the research development of π‐stacked molecular systems and introduces the new characteristics brought by the special molecular configuration and its application in organic semiconductors.
Compared to efficient green and near‐infrared light‐emitting diodes (LEDs), less progress has been made on deep‐blue perovskite LEDs. They suffer from inefficient domain various number of PbX6− ...layers (n) control, resulting in a series of unfavorable issues such as unstable color, multipeak profile, and poor fluorescence yield. Here, a strategy involving a delicate spacer modulation for quasi‐2D perovskite films via an introduction of aromatic polyamine molecules into the perovskite precursor is reported. With low‐dimensional component engineering, the n1 domain, which shows nonradiative recombination and retarded exciton transfer, is significantly suppressed. Also, the n3 domain, which represents the population of emission species, is remarkably increased. The optimized quasi‐2D perovskite film presents blue emission from the n3 domain (peak at 465 nm) with a photoluminescence quantum yield (PLQY) as high as 77%. It enables the corresponding perovskite LEDs to deliver stable deep‐blue emission (CIE (0.145, 0.05)) with an external quantum efficiency (EQE) of 2.6%. The findings in this work provide further understanding on the structural and emission properties of quasi‐2D perovskites, which pave a new route to design deep‐blue‐emissive perovskite materials.
A quasi‐two‐dimensional perovskite film with stable domain distribution is prepared based on a new spacer. The film containing pure bromide perovskite exhibits enhanced deep‐blue fluorescence with quantum yield of 77% by low‐dimensional component engineering. As a result, the corresponding light‐emitting diodes deliver stable deep‐blue emission with a peak external quantum efficiency of 2.6%.
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).
Multi‐layer π‐stacked emitters based on spatially confined donor/acceptor/donor (D/A/D) patterns have been developed to achieve high‐efficiency thermally activated delayed fluorescence (TADF). In ...this case, dual donor moieties and a single acceptor moiety are introduced to form two three‐dimensional (3D) emitters, DM‐BD1 and DM‐BD2, which rely on spatial charge transfer (CT). Owing to the enforced face‐to‐face D/A/D pattern, effective CT interactions are realized, which lead to high photoluminescence quantum yields (PLQYs) of 94.2 % and 92.8 % for the two molecules, respectively. The resulting emitters exhibit small singlet–triplet energy splitting (ΔEST) and fast reverse intersystem crossing (RISC) processes. Maximum external quantum efficiencies (EQEs) of 28.0 % and 26.6 % were realized for devices based on DM‐BD1 and DM‐BD2, respectively, which are higher than those of their D/A‐type analogues.
Multi‐Layer π‐stacked molecules are designed to realize efficient thermally activated delayed fluorescence. Spatially confined molecules with stereochemical structures are constructed in donor/acceptor/donor architectures with different conformations. Their organic light‐emitting diode (OLED) devices exhibit high external quantum efficiencies (EQEs) of 28.0 %/26.6 %, respectively.
Pharmacophore approaches have become one of the major tools in drug discovery after the past century's development. Various ligand-based and structure-based methods have been developed for improved ...pharmacophore modeling and have been successfully and extensively applied in virtual screening,
de novo design and lead optimization. Despite these successes, pharmacophore approaches have not reached their expected full capacity, particularly in facing the demand for reducing the current expensive overall cost associated with drug discovery and development. Here, the challenges of pharmacophore modeling and applications in drug discovery are discussed and recent advances and latest developments are described, which provide useful clues to the further development and application of pharmacophore approaches.
•The novel ultrathin hydrated V2O5·4VO2·2.72H2O nanobelts was obtained through a hydrothermal method.•The existence of crystal water can effectively improve performance.•V2O5·4VO2·2.72H2O delivers ...excellent cycling stability and the specific discharge capacity.•The high reversibility of Zn2+ insertion/extraction in V2O5·4VO2·2.72H2O was demonstrated by in-situ XRD.
Although rechargeable aqueous zinc-ion batteries (AZIBs) are emerging candidates for high energy density, safety and cost effectiveness large-scale energy storage, they still lack suitable cathodes with high rate capabilities. In the present work, ultrathin V2O5·4VO2·2.72H2O nanobelts were synthesized via a facile hydrothermal method as cathode materials for ZIBs. Benefiting from expanded interlayer spacing that results from crystal water, the V2O5·4VO2·2.72H2O cathode exhibits an improved capacity of 567 mAh·g−1 at 0.1 A·g−1 and superior rate capability of 10.0 A·g−1 with a decent capacity of 215 mAh·g−1. When at 10.0 A g−1, a capacity retention of 94.0% with respect to the initial specific capacity was retained after 1000 cycles, and 85.2% was obtained even after 2000 cycles. Furthermore, in-situ X-ray diffraction and various structural measurements proved the high reversibility of Zn2+ insertion and extraction in V2O5·4VO2·2.72H2O cathode. Further investigations show that ultrathin V2O5·4VO2·2.72H2O nanobelts have become a promising cathode material for the high-potential rechargeable AZIBs, and may clarify effective interlayer engineering strategies triggered by crystal water.
High-dimensional data analysis is a challenge for researchers and engineers in the fields of machine learning and data mining. Feature selection provides an effective way to solve this problem by ...removing irrelevant and redundant data, which can reduce computation time, improve learning accuracy, and facilitate a better understanding for the learning model or data. In this study, we discuss several frequently-used evaluation measures for feature selection, and then survey supervised, unsupervised, and semi-supervised feature selection methods, which are widely applied in machine learning problems, such as classification and clustering. Lastly, future challenges about feature selection are discussed.
Near‐infrared (NIR) organic solid‐state lasers play an essential role in applications ranging from laser communication to infrared night vision, but progress in this area is restricted by the lack of ...effective excited‐state gain processes. Herein, we originally proposed and demonstrated the cascaded occurrence of excited‐state intramolecular proton transfer for constructing the completely new energy‐level systems. Cascading by the first ultrafast proton transfer of <430 fs and the subsequent irreversible second proton transfer of ca. 1.6 ps, the stepwise proton transfer process favors the true six‐level photophysical cycle, which supports efficient population inversion and thus NIR single‐mode lasing at 854 nm. This work realizes longest wavelength beyond 850 nm of organic single‐crystal lasing to date and originally exploits the cascaded excited‐state molecular proton transfer energy‐level systems for organic solid‐state lasers.
Six‐level energy systems are constructed through the cascaded occurrence of excited‐state intramolecular proton transfer consisting of a first ultrafast proton transfer of <430 fs and a following dominant and irreversible proton transfer of ca. 1.6 ps, which support the NIR single‐mode lasing at 854 nm for exploiting energy‐level systems of OSSLs, especially at the NIR region from 780 to 2500 nm.
By analyzing Sounding of the Atmosphere using Broadband Emission Radiometry and the Modern‐Era Retrospective analysis for Research Applications Version 2 reanalysis observations from 2003 to 2020, we ...found that the structural variation of the westward quasi‐2‐day wave (Q2DW) is related to the mean zonal wind in the background atmosphere, and the zonal wavenumber 3 (W3) is more affected by the background atmosphere than the zonal wavenumber 4 (W4). Our study focuses on the spatial structure of ∼50–95 km and ∼50°S–50°N. The spatial structure of W3 and W4 in the Northern and Southern Hemispheres is unimodal and bimodal, while the bimodal structure of W3 in the Southern Hemisphere is more obvious in some years. In the unimodal structure, W3 has a higher (altitude) peak in the Southern Hemisphere (∼82 km) than in the Northern Hemisphere (∼70 km), while W4 peaks at ∼70 km in both hemispheres. In the bimodal structure, W3 in the Southern Hemisphere fluctuates mostly at ∼82 km, followed by ∼68 km, while W3 in the Northern Hemisphere fluctuates mostly at ∼70 km, followed by ∼82 km. The spatial structure of W4 in both hemispheres fluctuates mainly at ∼70 km, followed by ∼82 km. In addition, W3 is stronger in the Southern Hemisphere than the Northern Hemisphere, W4 is stronger in the Northern Hemisphere than the Southern Hemisphere, and peak amplitudes of both W3 and W4 are larger in a bimodal structure than unimodal structure. The diagnostic analysis shows that the interannual and interhemispheric structure changes of Q2DWs may be due to the larger mean flow instabilities, background winds, and refractive index in the mesosphere, which make the bimodal structure of W3 and W4 obtain larger energy for propagation and amplification, resulting in higher (altitude) and larger amplitudes. This indicates that the background atmosphere of the mesosphere can affect the spatial structure of Q2DWs.
Key Points
Wavenumber 3 (W3) and wavenumber 4 (W4) have unimodal and bimodal structural differences in the two hemispheres
The peak amplitudes of bimodal W3 and W4 are larger than those of unimodal W3 and W4 in both hemispheres
Variations in the background atmosphere are responsible for the interannual and interhemispheric structural variability
•VO2@N-doped carbon composites were obtained through a facile calcination process.•Amorphous N-doped carbon provides more active sites and higher conductivity.•VO2@N-doped carbon composites deliver ...excellent Electrochemical performance.•The reversibility of Zn2+ insertion/extraction were demonstrated by in-situ XRD.
The electrochemical performance of rechargeable aqueous zinc-ion batteries (AZIBs) to a great extent depends on the conductivity and structural stability of the cathode material. Herein, we report a facile calcination process to prepare the composite of VO2 and amorphous N-doped carbon using ultrathin V6O13 nanobelts coated with polydopamine as precursors. The amorphous structure of N-doped carbon enables the layered VO2@N-doped carbon composites to have more active sites and higher conductivity, and the amorphous structure has less structural change during ion diffusion. Therefore, the VO2@N-doped carbon composites exhibit excellent electrochemical performance. This work should open a new and efficient avenue for designing the cathodes of AZIBs with excellent performance.
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