Enhancement of Frster energy transfer from thermally activated delayed fluorophores layer to ultrathin phosphor layer for high color stability in non-doped hybrid white organic light-emitting devices

Fluorescence/phosphorescence hybrid white organic light-emitting devices（WOLEDs） based on double emitting layers（EMLs） with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence（TADF） layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone（DMAC-DPS） and an ultrathin non-doped yellow phosphorescence layer employing bis[2-（4-tertbutylphenyl）benzothiazolato-N,C2＇]iridium（acetylacetonate）（（tbt）_2Ir（acac））.Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline（Bphen） and 1,3,5-tris（2-Nphenylbenzimidazolyl） benzene（TPBi） are selected as the electron transporting layer（ETL）,and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l＇Eclairage（CIE） coordinates variation of（0.017,0.009） at a luminance ranging from 52 cd/m^2 to 6998 cd/m^2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency（EQE）,current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer（FRET）from DMAC-DPS to（tbt）_2Ir（acac） is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.

Highly efficient and non-doped red conjugated polymer dot for photostable cell imaging

By introducing a naphthothiadiazole(NT)unit as the main building block,a non-doped and red emissive conjugated polymer poly(9,9-dihexylfluorene-alt-naphthothiadiazole)(PFNT)is readily obtained through a two-step synthesis.Since the NT unit has a large twist angle with its neighboring segment,the aggregation-induced quenching(AIQ)effect of PFNT can be effectively suppressed in the condensed state.As a result,the corresponding PFNT polymer dot(Pdot)exhibits a high fluorescence quantum yield of53.2%with peak emission at 616 nm,which is one of the most efficient red Pdots known.PFNT Pdot shows good biocompatibility and can be employed for living cell fluorescent imaging with high brightness.It also can be used for specific subcellular organelle imaging through immunofluorescence labeling.Furthermore,the PFNT Pdot demonstrates much better photostability for long-time cell fluorescence imaging than commercial red dyes.The high performances of PFNT Pdot make it a promising fluorescent probe for practical bioapplications.

Fabrication of high-performance non-doped OLEDs by combining aggregation-induced emission and thermally activated delayed fluorescence

Undoubtedly,the realization of"one stone and two birds"is ideal,which is also applicable to the molecular design in the pursuit of excellent performance.Recently,this standpoint has been confirmed again by an interesting story written from the lab of Zujin Zhao,Shi-Jian Su,and BenZhong Tang,at South China University of Technology and the Hong Kong University of Science and Technology,in the design of DBT-BZ-DMAC(Figure 1)[1].Despite its simple structure,DBT-BZ-DMAC exhibits wonderful characteristics,

Structural Controls of Tetraphenylbenzene-based AIEgens for Non-doped Deep Blue Organic Light-emitting Diodes

Aggregation-induced emission(AIE)has emerged as a new concept,giving highly efficient solid-state photoluminescence.Particularly,AIE luminogens(AIEgens)with deep blue emission(400–450 nm)have displayed salient advantages for non-doped organic light-emitting diodes(OLEDs).However,deep blue emitters with Commission Internationale de L’Eclairage(CIE)coordinates less than 0.08 are still rare.In this review,we outline the latest achievements in the molecular guidelines based on the AIE core of tetraphenylbenzene(TPB)for developing efficient deep blue AIEgens.We provide insights into the construction of deep blue emitters with high horizontal orientation by regulating the length of the linear molecule.We also discuss the luminescence mechanisms of these AIEgens-based OLEDs by using the magnetic field effects measurements.Finally,a summary of the challenges and perspectives of deep blue AIEgens for non-doped OLEDs is also presented.

New electron-donating segment to develop thermally activated delayed fluorescence emitters for efficient solution-processed non-doped organic light-emitting diodes

Thermally activated delayed fluorescent(TADF) materials capable of efficient solution-processed nondoped organic light-emitting diodes(OLEDs) are of important and practical significance for further development of OLEDs. In this work, a new electron-donating segment, 2,7-di(9 H-carbazol-9-yl)-9,9-dimethyl-9,10-dihydroacridine(2 Cz-DMAC), was designed to develop solution-processable non-doped TADF emitters. 2 Cz-DMAC can not only simultaneously increase the solubility of compounds and suppress harmful aggregation-caused quenching, but also efficiently broaden the delocalization of the highest occupied molecular orbital and promote the reverse intersystem crossing process. Three new TADF emitters, 2-(2,7-di(9 H-carbazol-9-yl)-9,9-dimethylacridin-10(9 H)-yl)dibenzo[b,d]thiophene 5,5-dioxide(2 Cz-DMAC-BTB), 2-(2,7-di(9 H-carbazol-9-yl)-9,9-dimethylacridin-10(9 H)-yl)-9 H-thioxanthen-9-one(2 Cz-DMAC-TXO), 2-(2,7-di(9 H-carbazol-9-yl)-9,9-dimethylacridin-10(9 H)-yl)thianthrene 5,5,10,10-tetraoxide(2 Cz-DMAC-TTR), were developed by using 2 Cz-DMAC segment as the electron-donor. As anticipated, the solution-processed non-doped OLEDs employing 2 Cz-DMAC-BTB, 2 Cz-DMAC-TXO and 2 CzDMAC-TTR as the emitters respectively exhibited green, orange and red emissions with maximum external quantum efficiencies of 14.0%, 6.6% and 2.9%. These results successfully demonstrate the feasibility and convenience of developing efficient solution-processable non-doped TADF emitters based on 2 CzDMAC segment.

Quinoline-based aggregation-induced delayed fluorescence materials for highly efficient non-doped organic light-emitting diodes

Three new emitters,namely 10,10’-(quinoline-2,8-diyl)bis(10 H-phenoxazine)(Fene),10,10’-(quinoline-2,8-diyl)bis(10 H-phenothiazine)(Fens) and 10,10’-(quinoline-2,8-diyl)bis(9,9-dimethyl-9,10-dihydroacridine)(Yad),featuring quinoline as a new electron acceptor have been designed and conveniently synthesized.These emitters possessed small singlet-triplet splitting energy(ΔEst) and twisted structures,which not only endowed them show thermally activated delayed fluorescence(TADF)properties but also afforded a remarkable aggregation-induced emission(AIE) feature.Moreover,they also showed aggregation-induced delayed fluorescence(AIDF) property and good photoluminescence(PL) property,which are the ideal emitters for non-doped organic light-emitting diodes(OLEDs).Furthermore,high-performance non-doped OLEDs based on Fene,Fens and Yad were achieved,and excelle nt maximum external quantum efficiencies(EQEmax) of 14,9%,13.1% and 17,4%,respectively,were obtained.It was also found that all devices exhibited relatively low turn-on voltages ranging from 3.0 V to3.2 V probably due to their twisted conformation and the AIDF properties.These results demonstrated the quinoline-based emitters could have a promising application in non-doped OLEDs.

Endowing imidazole derivatives with thermally activated delayed fluorescence and aggregation-induced emission properties for highly efficient non-doped organic light-emitting diodes

The development and enrichment of high-performance organic fluorophores that simultaneously possess thermally activated delayed fluorescence(TADF)and aggregation-induced emission(AIE)properties is going pursued but remains a great challenge due to severe exciton quenching.Herein,a systematical investigation on imidazole moiety has successfully given rise to a series of highly efficient imidazolebased TADF-AIE luminogens for the first time.The attachment of two cyano functionalities on imidazole moiety can significantly increase the electron-withdrawing ability,so as to realize TADF emissions with small singlet-triplet energy gaps(ΔEST)values.Meanwhile,the installation of a steric hindrance group at N1 position of imidazole moiety can twist the geometry between imidazole and phenyl bridge,thus transforming imidazole derivative from an aggregation-caused quenching emitter into an AIE luminogen.Consequently,the non-doped organic light-emitting diodes(OLEDs)utilizing these TADF-AIE luminogens as emitters exhibit outstanding skyblue and green emissions,with external quantum efficiency(EQE)as high as 20.0%and low efficiency roll-off(EQE at 1000 cd m−2,16.1%).These values represent the state-of-the-art performance for all imidazole-based OLED devices,which illustrates the significant potential of imidazole derivatives in assembling high-performance OLEDs.

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.