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.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Charge-transfer (CT) complexes, formed by electron transfer from a donor to an acceptor, play a crucial role in organic semiconductors. Excited-state CT complexes, termed exciplexes, harness both ...singlet and triplet excitons for light emission, and are thus useful for organic light-emitting diodes (OLEDs). However, present exciplex emitters often suffer from low photoluminescence quantum efficiencies (PLQEs), due to limited control over the relative orientation, electronic coupling and non-radiative recombination channels of the donor and acceptor subunits. Here, we use a rigid linker to control the spacing and relative orientation of the donor and acceptor subunits, as demonstrated with a series of intramolecular exciplex emitters based on 10-phenyl-9,10-dihydroacridine and 2,4,6-triphenyl-1,3,5-triazine. Sky-blue OLEDs employing one of these emitters achieve an external quantum efficiency (EQE) of 27.4% at 67 cd m
with only minor efficiency roll-off (EQE = 24.4%) at a higher luminous intensity of 1,000 cd m
. As a control experiment, devices using chemically and structurally related but less rigid emitters reach substantially lower EQEs. These design rules are transferrable to other donor/acceptor combinations, which will allow further tuning of emission colour and other key optoelectronic properties.
Full text
Available for:
FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
White‐light‐emissive organic micro/nanostructures hold exotic potential applications in full‐color displays, on‐chip wavelength‐division multiplexing, and backlights of portable display devices, but ...are rarely realized in organic core/shell heterostructures. Herein, through regulating the noncovalent interactions between organic semiconductor molecules, a hierarchical self‐assembly approach of horizontal epitaxial‐growth is demonstrated for the fine synthesis of organic core/mono‐shell microwires with multicolor emission (red–green, red–blue, and green–blue) and especially organic core/double‐shell microwires with radial red–green–blue (RGB) emission, whose components are dibenzog,pchrysene (DgpC)‐based charge‐transfer (CT) complexes. In fact, the desired lattice mismatching (≈2%) and the excellent structure compatibility of these CT complexes facilitate the epitaxial‐growth process for the facile synthesis of organic core/shell microwires. With the RGB‐emissive substructures, these core/double‐shell organic microwires are microscale white‐light sources (CIE 0.34, 0.36). Besides, the white‐emissive core/double‐shell microwires demonstrate the fascinating full‐spectrum light transportation from 400 to 700 nm. This work indeed opens up a novel avenue for the accurate construction of organic core/shell heterostructures, which provides an attractive platform for the organic integrated optoelectronics.
Through regulating the noncovalent interactions between organic semiconductor molecules (|ECT, DgpC‐TCNB = −18.35 kcal mol−1| > |ECT, DgpC‐TFP = −13.45 kcal mol−1| > |Eπ–π, DgpC = −6.81 kcal mol−1|), a hierarchical self‐assembly approach of horizontal epitaxial‐growth is demonstrated for the precise synthesis of organic core/double‐shell microwires with radial red–green–blue (RGB) substructures for miniaturized white‐light sources (CIE 0.34, 0.36).
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A multiple resonance thermally activated delayed fluorescence (MR‐TADF) molecule with a fused, planar architecture tends to aggregate at high doping ratios, resulting in broad full width at half ...maximum (FWHM), redshifting electroluminescence peaks, and low device efficiency. Herein, we propose a mono‐substituted design strategy by introducing spiro‐9,9′‐bifluorene (SBF) units with different substituted sites into the MR‐TADF system for the first time. As a classic steric group, SBF can hinder interchromophore interactions, leading to high device efficiency (32.2–35.9 %) and narrow‐band emission (≈27 nm). Particularly, the shield‐like molecule, SF1BN, seldom exhibits a broadened FWHM as the doping ratio rises, which differs from the C3‐substituted isomer and unhindered parent emitter. These results manifest an effective method for constructing highly efficient MR‐TADF emitters through a spiro strategy and elucidate the feasibility for steric modulation of the spiro structure in π‐framework.
By incorporating a three‐dimensional spiro unit into multiple resonance thermally activated delayed fluorescence emitters, the device efficiency is increased to nearly 1.5 times that of the unhindered emitter. Notably, the linkage pattern with spatial interaction and hindrance can maintain the narrow FWHM and curb unfavorable redshifts at a high doping ratio.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Several studies show that the immunosuppressive drugs targeting the interleukin-6 (IL-6) receptor, including tocilizumab, ameliorate lethal inflammatory responses in COVID-19 patients infected with ...SARS-CoV-2. Here, by employing single-cell analysis of the immune cell composition of two severe-stage COVID-19 patients prior to and following tocilizumab-induced remission, we identify a monocyte subpopulation that contributes to the inflammatory cytokine storms. Furthermore, although tocilizumab treatment attenuates the inflammation, immune cells, including plasma B cells and CD8
T cells, still exhibit robust humoral and cellular antiviral immune responses. Thus, in addition to providing a high-dimensional dataset on the immune cell distribution at multiple stages of the COVID-19, our work also provides insights into the therapeutic effects of tocilizumab, and identifies potential target cell populations for treating COVID-19-related cytokine storms.
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.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Metal halide perovskite semiconductors have demonstrated remarkable potentials in solution‐processed blue light‐emitting diodes (LEDs). However, the unsatisfied efficiency and spectral stability ...responsible for trap‐mediated non‐radiative losses and halide phase segregation remain the primary unsolved challenges for blue perovskite LEDs. In this study, it is reported that a fluorene‐based π‐conjugated cationic polymer can be blended with the perovskite semiconductor to control film formation and optoelectronic properties. As a result, sky‐blue and true‐blue perovskite LEDs with Commission Internationale de l'Eclairage coordinates of (0.08, 0.22) and (0.12, 0.13) at the record external quantum efficiencies of 11.2% and 8.0% were achieved. In addition, the mixed halide perovskites with the conjugated cationic polymer exhibit excellent spectral stability under external bias. This result illustrates that π‐conjugated cationic polymers have a great potential to realize efficient blue mixed‐halide perovskite LEDs with stable electroluminescence.
A fluorene‐based π‐conjugated cationic polymer as a multifunctional passivator to suppress non‐radiative processes, improve charge transport properties, and inhibit ion migration for blue mixed‐halide perovskite semiconductors, is reported. As a result, efficient and spectrally stable blue perovskite light‐emitting diodes with emission wavelengths from 485 to 458 nm are achieved.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Harvesting the narrow bandgap excitons of charge‐transfer (CT) complexes for the achievement of near‐infrared (NIR) emission has attracted intensive attention for its fundamental importance and ...practical application. Herein, the triphenylene (TP)‐2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) CT organic complex is designed and fabricated via the supramolecular self‐assembly process, which demonstrates the NIR emission with a maximum peak of 770 nm and a photoluminescence quantum yield (PLQY) of 5.4%. The segregated stacking mode of TP‐F4TCNQ CT complex based on the multiple types of intermolecular interaction has a low CT degree of 0.00103 and a small counter pitch angle of 40° between F4TCNQ and TP molecules, which breaks the forbidden electronic transitions of CT state, resulting in the effective NIR emission. Acting as the promising candidates for the active optical waveguide in the NIR region beyond 760 nm, the self‐assembled TP‐F4TCNQ single‐crystalline organic microwires display an ultralow optical‐loss coefficient of 0.060 dB µm−1. This work holds considerable insights for the exploration of novel NIR‐emissive organic materials via an universal “cocrystal engineering” strategy.
Through changing mixed stacking into segregated stacking mode, triphenylene (TP)‐2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) charge‐transfer (CT) complex demonstrates a low CT degree and a small counter pitch angle between TP and F4TCNQ molecules, benefiting for breaking the forbidden electronic transitions of CT state for realizing the near‐infrared emission with a maximum peak of 770 nm and a photoluminescence quantum yield of 5.4%.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Immune checkpoint blockade has become a promising therapeutic approach to reverse immune cell exhaustion. Coinhibitory CD96 and T‐cell immunoglobulin and ITIM domain (TIGIT), together with ...costimulatory CD226, bind to common ligand CD155. The balancing between three receptors fine‐tunes immune responses against tumors. In this study, we investigated the expression of CD96, TIGIT, and CD226 in 55 fresh human hepatocellular carcinoma (HCC) samples, 236 paraffin‐embedded HCC samples, and 20 normal human livers. The cumulative percentage, absolute count, and mean fluorescence intensity (MFI) of CD96+ NK cells are significantly increased in the intratumoral tissues of HCC and break the balance between three receptors. Human CD96+ NK cells are functionally exhausted with impaired interferon‐gamma (IFN‐γ) and tumor necrosis factor‐alpha (TNF‐α) production, high gene expression of interleukin (IL)‐10 and transforming growth factor‐beta 1 (TGF‐β1), and low gene expression of T‐bet, IL‐15, perforin, and granzyme B. In addition, blocking CD96‐CD155 interaction specifically increases lysis of HepG2 cells by NK cells. HCC patients with a high level of CD96 or CD155 expression within tumor are strongly associated with deteriorating disease condition and shorter disease‐free survival (DFS) and overall survival times. Patients with a higher cumulative percentage of CD96+ NK cells within tumor also exhibit shorter DFS. High plasma level of TGF‐β1 in HCC patients up‐regulates CD96 expression and dynamically shifts the balance between CD96, TIGIT, and CD226 in NK cells. Blocking TGF‐β1 specifically restores normal CD96 expression and reverses the dysfunction of NK cells. Conclusion: These findings indicate that human intratumoral CD96+ NK cells are functionally exhausted and patients with higher intratumoral CD96 expression exhibit poorer clinical outcomes. Blocking CD96‐CD155 interaction or TGF‐β1 restores NK cell immunity against tumors by reversing NK cell exhaustion, suggesting a possible therapeutic role of CD96 in fighting liver cancer.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Double-stranded RNA (dsRNA) is a potent proinflammatory signature of viral infection. Long cytosolic dsRNA is recognized by MDA5. The cooperative assembly of MDA5 into helical filaments on dsRNA ...nucleates the assembly of a multiprotein type I interferon signaling platform. Here, we determined cryoelectron microscopy (cryo-EM) structures of MDA5-dsRNA filaments with different helical twists and bound nucleotide analogs at resolutions sufficient to build and refine atomic models. The structures identify the filament-forming interfaces, which encode the dsRNA binding cooperativity and length specificity of MDA5. The predominantly hydrophobic interface contacts confer flexibility, reflected in the variable helical twist within filaments. Mutation of filament-forming residues can result in loss or gain of signaling activity. Each MDA5 molecule spans 14 or 15 RNA base pairs, depending on the twist. Variations in twist also correlate with variations in the occupancy and type of nucleotide in the active site, providing insights on how ATP hydrolysis contributes to MDA5-dsRNA recognition.
Display omitted
•Cryo-EM structures of MDA5-dsRNA filaments determined for three catalytic states•Filament forming interfaces are flexible and predominantly hydrophobic•Mutation of filament-forming residues can cause loss or gain of IFN-β signaling•ATPase cycle is coupled to changes in filament twist and size of the RNA footprint
Cryo-EM structures determined by Yu et al. show how the innate immune sensor MDA5 forms helical filaments to recognize cytosolic double-stranded RNA. Mutations at the hydrophobic filament interface can cause loss or gain of signaling activity. ATP binding and hydrolysis cause structural changes, which are proposed to confer proofreading activity.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
