Heptagonal intramolecular-lock strategy enables high-performance thermally activated delayed fluorescence emitters

The development of highly efficient thermally activated delayed fluorescence(TADF)emitters is persistently pursued for the application of organic light-emitting diodes(OLED)in full-colour display and solid-state lighting.Herein,we present a heptagonal intramolecular-lock strategy to design high-performance TADF emitters.As a proof-of-concept,a new type of tribenzotropone(TBP)acceptor has been designed and synthesized by a cascade decarboxylative cyclization of aryl oxoacetic acid derivative with biphenyl boronic acid.Compared with the unlocked benzophenone(BP)acceptor,the TBP acceptor has a highly twisted heptagonal geometry with moderate rigidity and flexibility,which enables a high-performance TADF emitter with a small single-triplet energy gap(ΔE_(ST))of 0.04 e V,a high photoluminescence quantum yield(Φ_(PL))of 99% and a large horizontal orientation factor(Θ_(//))of 84.0%.Consequently,highly efficient OLEDs with an external quantum efficiency as high as 33.8% are assembled,which is significantly higher than those of DPAC-BP with a highly rotatable BP acceptor(23.8%)as well as DPACFO with a rigid fluorenone(FO)acceptor(6.9%).

An efficient aggregation-enhanced delayed fluorescence luminogen created with spiro donors and carbonyl acceptor for applications as an emitter and sensitizer in high-performance organic light-emitting diodes

Organic light-emitting diodes(OLEDs)fabricated using organic thermally activated delayed fluorescence materials as sensitizers have recently achieved significant advancements,but the serious efficiency roll-offs are still troublesome in most cases.Herein,a tailor-made multifunctional luminogen SBF-BP-SFAC containing 9,9′-spirobifluorene(SBF)and spiro[acridine-9,9-fluorene](SFAC)as electron donors and carbonyl as an electron acceptor is synthesized and characterized.SBF-BPSFAC has the advantages of high thermal stability,aggregation-enhanced delayed fluorescence,and balanced carrier transport ability,and prefers horizontal dipole orientation.Highly efficient OLEDs employing SBF-BP-SFAC as an emitter radiate intense cyan light with outstanding external quantum efficiencies(ηexts)of up to 30.6%.SBF-BP-SFAC can also serve as an excellent sensitizer for orange fluorescence,phosphorescence,and delayed fluorescence materials,providing excellent η exts of up to 30.3% with very small efficiency roll-offs due to the fast Förster energy transfer as well as exciton annihilation suppression by bulky spiro donors.These outstanding performances demonstrate the great potential of SBF-BP-SFAC as an emitter and sensitizer for OLEDs.

Stably doped graphene transparent electrode with improved lightextraction for efficient flexible organic light-emitting diodes

Graphene-based flexible transparent electrodes(FTEs)are promising candidate materials for developing next-generation flexible organic light-emitting diodes(OLEDs).However,the quest for high-efficiency OLEDs is hindered by the low light-extraction and charge injection efficiencies of graphene electrode.Here,we combine the frustrated Lewis pair doping with nanostructure engineering to obtain high-performance graphene FTE.A p-type dopant aci-nitromethane-tris(pentafluorophenyl)borane(ANBCF)was synthesized and deposited on graphene FTE to form an aperiodic nanostructure,which not only improves the light-extraction but also stably p-dopes graphene to enhance its hole injection.The use of ANBCF-doped graphene as the anode enables high-efficiency flexible green OLEDs with external quantum efficiency(EQE)and power efficiency(PE)out-performing most flexible graphene OLEDs of comparable structure.This study provides a simple and effective pathway to fabricate high-performance graphene FTEs for efficient flexible OLEDs.

Towards Efficient Blue DelayedFluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Constructing blue thermally activated delayedfluorescence materials for high-performance organic light-emitting diodes(OLEDs)remains challenging due to the intrinsically strong intramolecular charge transfer nature of the nearly orthogonal connection of electron donor(D)and acceptor(A),which results in long-wavelength emission.Herein,an effective delayed-fluorescence design strategy of modulating D–A torsion angles is proposed and efficient sky-blue,pure-blue,and deep-blue delayed-fluorescence molecules consisting of a xanthenone acceptor and carbazole-based donors are created by decreasing the torsion angles.They exhibit strong delayed fluorescence with high photoluminescence quantum yields of 85–94%in doped films,and their delayed-fluorescence lifetimes are elongated from 1.0 to 27.6μs as the torsion angles decrease.These molecules can function as excellent emitters in OLEDs,providing efficient electroluminescence peaking at 442 nm(CIEx,y=0.15,0.08),462 nm(CIEx,y=0.15,0.18),and 482 nm(CIEx,y=0.17,0.30)with state-of-the-art external quantum efficiencies of up to 22.2%,33.7%,and 32.1%,respectively,demonstrating the proposed molecular design for efficient blue delayed-fluorescence molecules is successful and promising.

Greatly increased visible-light photocatalytic activity of SnS_(2)/carbon nanotube composite for Cr(VI)reduction:Insights into effects of solid acid structure

A composite of SnS_(2)and carbon nanotube(CNT)was successfully synthesized as a visible-light-driven photocatalyst with a mechanochemical method.In comparing with SnS_(2),the SnS_(2)/CNT composite im-proved much the photocatalytic removal of Cr(VI)in acidic condition,which was confirmed to its special solid acid structure.During the synthesis of the SnS_(2)/CNT composite by ball milling,S-C p-πbonding was formed between sulfur atoms in SnS_(2)and carbon atoms in CNT.The generated S-C p-πbonding enhanced the transfer of photo-induced electrons in the bulk phase of the composite photocatalyst un-der visible light irradiation.Moreover,the persistent radical sites on CNT were able to trap photo-induced electrons and served as conjugated acid sites in the photocatalysis,which increased surface concentration of protons through their association with H+.These made the catalyst have a solid acid structure with plentiful surface protons,promoting the interfacial electron transfer between the catalysts and Cr(VI)and increasing the source of H+for the reduction of Cr(VI).As a result,the photocatalytic reduction rate of Cr(VI)on the SnS_(2)/CNT composite were dramatically enhanced,being about 800%that on SnS_(2).On the basis of various characterizations and probe experiments,we confirmed the significance of the solid acid structure of the photocatalyst and clarified the catalytic mechanism of the new photocatalyst.Our finding may provide a new strategy to prepare highly active photocatalysts for proton-involved reactions.

聚集诱导发光

聚集诱导发光(AIE)是唐本忠院士于2001年提出的一个科学概念,是指一类在溶液中不发光或者发光微弱的分子聚集后发光显著增强的现象。高效固态发光的AIE材料有望从根本上解决有机发光材料面临的聚集导致发光猝灭难题,具有重大的实际应用价值。从分子内旋转受限到分子内运动受限,从聚集诱导发光到聚集体科学,AIE领域已经取得了许多原创性的成果。在本综述中,我们从AIE材料的分类、机理、概念衍生、性能、应用和挑战等方面讨论了AIE领域最近取得的显著进展。希望本综述能激发更多关于分子聚集体的研究,并推动材料、化学和生物医学等学科的进一步交叉融合和更大发展。

Substituent engineering in g-C_(3)N_(4)/COF heterojunctions for rapid charge separation and high photo-redox activity

The heterojunction composed of covalent organic frameworks(COFs)with adjustable structure and other photocatalysts has great potential in the field of photocatalysis.However,effectively enhancing the photocatalytic performance of organic heterojunctions by designing the structure of COFs has not been explored.Herein,TPB-TP-COFs fabricated from 1,3,5-tris(4-amino-phenyl)benzene(TPB)and terephthalaldehyde(TP)with different substituents(−H,−OH,−OCH_(3),−Br and−F groups),were applied to construct g-C_(3)N_(4)/COFs.The performance improvement of the heterojunction could be affected by substituents,and only−OCH_(3) groups can significantly improve both the photocatalytic phenol oxidation and Cr(Ⅵ)reduction.DFT calculation demonstrated that the substituents will affect the electron cloud distribution of CBM,and the location of CBM in the TPB segment is beneficial for the charge transport between TPB-TP-OCH_(3) and g-C_(3)N_(4).The enhanced charge transfer from g-C_(3)N_(4) to TPB segment and the improved light absorption of TPB-TP-OCH_(3) jointly optimize the photocatalytic redox capacity of g-C_(3)N_(4)/TPB-TP-OCH_(3).On the basis of this study,regulating the electronic effects of semiconductors played a vital role in improving photocatalytic performance in organic heterojunctions.

Organic-inorganic hybrid Sn-based perovskite photodetectors with high external quantum efficiencies and wide spectral responses from 300 to 1000 nm

Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap(1.6 e V) limits their photonharvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W^-1, a specific detectivity of 7×10^12 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of350–900 nm, with a maximum value of about 80% at 550 nm.

High efficiency yellow fluorescent organic light emitting diodes based on m-MTDATA/BPhen exciplex

High efficient yellow organic light emitting diodes （OLEDs） based on exciplex were reported. The exciplex was formed by 4, 4＇, 4″-tris β-methylphenyl （phenyi） amino]-triphenylamine （m-MTDATA） and 4, 7- diphenyl-1, 10-phenanthroline （BPhen）. The resulting yellow OLEDs exhibited an external quantum efficiency of over 7%, which is attributed to the effective energy back transfer from exciplex triplet state to exciplex singlet state. The maximum power efficiency of 25 lm/W was achieved. Doping a yellow phosphor Ir（bt）2（acac） into m-MTDATA： BPhen blend, a high efficiency device was achieved with a turn-on voltage of 2.1 V, maximum power efficiency and external quantum efficiency of 86.1 lm/W and 20.7%, respectively.

Exceptionally efficient deep blue anthracene-based luminogens:design,synthesis,photophysical,and electroluminescent mechanisms

Achieving high-efficiency deep blue emitter with CIE_(y)<0.06(CIE,Commission Internationale de L’Eclairage)and external quantum efficiency(EQE)>10%has been a long-standing challenge for traditional fluorescent materials in organic light-emitting diodes(OLEDs).Here,we report the rational design and synthesis of two new deep blue luminogens:4-(10-(4’-(9 H-carbazol-9-yl)-2,5-dimethyl-[1,1’-biphe nyl]-4-yl)anthracen-9-yl)benzonitrile(2 M-ph-pCzAnBzt)and 4-(10-(4-(9 H-carbazol-9-yl)-2,5-dimethyl phenyl)anthracen-9-yl)benzonitrile(2 M-pCzAnBzt).In particular,2 M-ph-pCzAnBzt produces saturated deep blue emissions in a non-doped electroluminescent device with an exceptionally high EQE of 10.44% and CIE_(x,y)(0.151,0.057).The unprecedented electroluminescent efficiency is attributed to the combined effects of higher-order reversed intersystem crossing and triplet-triplet up-conversion,which are supported by analysis of theoretical calculation,triplet sensitization experiments,as well as nanosecond transient absorption spectroscopy.This research offers a new approach to resolve the shortage of high efficiency deep blue fluorescent emitters.

Utilizing Electroplex Emission to Achieve External Quantum Efficiency up to 18.1% in Nondoped Blue OLED

For the first time,electroplex emission is utilized to enhance the performance of nondoped blue organic light-emitting diodes(OLEDs).By decorating the twisted blue-emitting platform and adjusting the electronic structure,three molecules of 3Cz-Ph-CN,3Cz-mPh-CN,and 3Ph-Cz-CN with a donor-acceptor structure are synthesized and investigated.When external voltage is applied,electroplex emission,which contributes to the emission performance of OLED,can be realized at the interface between the emitting layer and the electron-transporting layer.Accordingly,high external quantum efficiency of 18.1%can be achieved,while the emission wavelength of the device can be controlled in the blue region.Our results provide the possibility to enhance the performance of OLED through electroplex emission,in addition to the generally investigated thermally activated delayed fluorescence(TADF).Excitedly,when 3Ph-Cz-CN is used as host material in orange-emitting phosphorous OLEDs(PO-01 as the dopant),unprecedented high external quantum efficiency of 27.4%can also be achieved.

Planar pn heterojunction organic light-emitting diodes

Organic light-emitting diodes（OLEDs）are being increasingly applied in flat-panel displays,such as television and mobile phones,and have great potential to become next generation solid-state lighting sources.

Improved transient electroluminescence technique based on time-correlated single-photon counting technology to evaluate organic mobility

The transient electroluminescence(EL)technique is widely used to evaluate the carrier mobility in the field of organic light emitting diodes.The traditional analog detection strategy using oscilloscopes is generally limited since the background noise causes an underestimation of the mobility value.In this paper,we utilize time-correlated single-photon counting(TCSPC)to probe the transient EL for mobility calculation.The measurements on tris(8-hydroxyquinoline)aluminum(Alq3)show that the electron mobilities obtained using the TCSPC technique are slightly higher than those obtained from the analog method at all the investigated voltages.Moreover,the TCSPC mobilities demonstrate weaker dependence on the root of electrical field compared to the oscilloscope mobilities.These improvements are attributed to the unique principle of TCSPC,which quantifies the EL intensity by counting the number of single-photon pulses,improving its single-photon sensitivity and elimi-nating the negative impacts of electrical noise.These advantages make TCSPC a powerful technique in the characterization of time-resolved electroluminescence.

Three-dimensional organic cage with aggregation-induced delayed fluorescence

A new kind of emissive small-molecular organic cage has been developed via the combination of coupling and condensation reactions,which shows outstanding solubility,structural stability and potential spatial isomeric chirality.Interestingly,through the introduction of proper donor and acceptor units,this emissive organic cage is the first among organic cages to exhibit red aggregation-induced delayed fluorescence with photoluminescence emission at 603 nm.The finding not only expands the types of emissive small-molecular organic cages,but also represents an important step for further development of red delayed fluorescence materials with good solubility and aggregation-induced emission feature.

Three-dimensional organic cage with narrowband delayed fluorescence

A new type of simple emissive organic cage consisting of diphenyl sulfone units and nitrogen atoms was developed via one-pot C–N coupling condensation or two-step reactions along with a series of sulfoxide cages obtained, which exhibited excellent chemical modifiability and structural stability. By precisely controlling the participation of donor and acceptor units, a highly soluble organic cage with delayed fluorescence was obtained for the first time. More interestingly, due to the restriction of intramolecular flipping by locking the building blocks within a rigid framework, this emissive organic cage further showed narrowband ultra-deep blue electroluminescence emission at 413 nm with a full-width at half-maximum of 35 nm. This finding not only expands the family of electroluminescent organic cages, but also opens up a new platform for delayed fluorescence materials with high solubility and color purity.