Red thermally activated delayed fluorescence(TADF)emitters are essential for the development of organic light-emitting diodes(OLEDs).To better understand and develop red TADF emitters,herein,the effect of quasi-degenerate orbital distribution was inves-tigated on their performance.Two red TADF emitters 10,10'-(11,12-difluorodibenzo[a,c]phenazine-3,6-diyl)bis(10H-phenoxazine)(DPXZ-BPF)and 10,10',10"-(12-fluorodibenzo[a,c]phenazine-3,6,11-triyl)tris(10H-phenoxazine)(TPXZ-BPF)were constructed by combining two or three phenoxazine(PXZ)donor units with a rigid coplanar acceptor core.As expected,a couple of PXZ units can induce quasi-degenerate orbital distribution by virtue of the high steric hindrance between each donor unit and acceptor core,which enables multiple excited states engaged in the reverse intersystem crossing(RISC)process.Consequently,DPXZ-BPF and TPXZ-BPF exhibit fast RISC rates(kRISCs)of 1.07×106 s-1 and 1.29×106 s-1 and high PLQYs of 74.6％and 81.1％,respectively.And the higher kRISC and PLQY of TPXZ-BPF are mainly attributed to the additional quasi-degenerate orbitals,which further enhance the tri-plet RISC process and the singlet radiative process.As a result,TPXZ-BPF-based OLEDs achieved improved efficiencies with a red-shifted emission compared with DPXZ-BPF-based OLEDs.These results demonstrated the tremendous potential of introducing quasi-degenerate orbital distribution in developing red TADF emitters.

Hao-Yu Yang;Ming Zhang;Jue-Wen Zhao;Chun-Peng Pu;Hui Lin;Si-Lu Tao;Cai-Jun Zheng;Xiao-Hong Zhang

School of Optoelectronic Science and Engineering,University of Electronic Science and Technology of China,Chengdu,Sichuan 610054,China;Institute of Functional Nano&Soft Materials(FUNSOM),Soochow University,Suzhou,Jiangsu 215123,China

中国化学（英文版）

[1]Hao-Yu Yang;Ming Zhang;Jue-Wen Zhao;Chun-Peng Pu;Hui Lin;Si-Lu Tao;Cai-Jun Zheng;Xiao-Hong Zhang-.Improving Efficiency of Red Thermally Activated Delayed Fluorescence Emitter by Introducing Quasi-Degenerate Orbital Distribution)[J].中国化学（英文版）,2022(08):911-917

difluorodibenzo,phenoxazine,DPXZ,fluorodibenzo,TPXZ,PXZ,kRISCs

Improving,Efficiency,Red,Thermally,Activated,Delayed,Fluorescence,Emitter,by,Introducing,Quasi,Degenerate,Orbital,Distribution,thermally,activated,delayed,fluorescence,TADF,emitters,essential,development,organic,light,emitting,diodes,OLEDs,To,better,understand,herein,effect,quasi,degenerate,distribution,was,inves,tigated,their,performance,Two,phenazine,diyl,bis,10H,BPF,triyl,tris,were,constructed,combining,two,three,donor,units,rigid,coplanar,acceptor,core,expected,couple,can,induce,virtue,steric,hindrance,between,each,which,enables,multiple,excited,states,engaged,reverse,intersystem,crossing,process,Consequently,exhibit,fast,rates,PLQYs,respectively,And,higher,mainly,attributed,additional,orbitals,further,enhance,plet,singlet,radiative,achieved,improved,efficiencies,shifted,emission,compared,These,results,demonstrated,tremendous,potential,introducing,developing

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