Preparation And Properties Of D/A Exciplex Delayed-Fluorescence Materials

The D-A molecular system has obvious intramolecular/intermolecular charge transfer(CT)properties,which is very suitable for the small EST used in TADF emission by separated HOMO and LUMO without the need for heavy metals.In OLED devices,the intermolecular D-A structure formed by charge transfer between electron donor(D)and electron acceptor(A)is called exciplex under the action of electrical excitation.Kinite complex emission has been widely used in regulating OLED emission color or in providing white light.Based on 9H-carbazole,3,6-2 tertiary butyl carbazole,indole as initial reaction raw materials,three new synthesized organic compounds:1,3,5-tri(9H-carbazol-9-yl)benzene,1,3,5-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)benzene,1,3,5-tri(1H-indole-1yl)benzene.These new compounds were characterized by 1H NMR,13C NMR,high resolution spectrometry and the thermal,electrochemical and optical properties and quantitative calculation results were studied.Thermogravimetric test results showed that the decomposition temperatures of the three compounds were 263.34,256.95 and 251.16,indicating that 1,3,5-tri(3,6-di-tert-butyl-9H-carbazol-9-y)benzene had an outstanding stability.The HOMO,LUMO and band gap of 1,3,5-tri(9H-carbazol-9-yl)benzene are-5.51 eV,-2.51 eV,3.00 eV.HOMO,LUMO and band gap of 1,3,5-tris(3,6-di-t-ert-9H-carbazol-9-yl)benzene are-5.18 eV,-2.28 eV,2.90 eV;the HOMO,LUMO and band gap of 1,3,5-tri(1H-indol-1-yl)benzene is-5.09 eV,-2.16eV and 2.93 eV.The strongest absorption peak of the UV-visible absorption spectra of the three compounds in different solvents is located within 290-310 nm.The peak fluorescence emission of the fluorescence spectrum of the three compounds in different solvents is between 345 and 365 nm,suggesting that the compound is a purple luminescent material.Among them,the highest fluorescence quantum efficiency is 39.8%(in acetonitrile)of 1,3,5-tri(9H-carbazol-9-yl).Bphen has a low LUMO level and a high number of available acceptors,and is commonly used as a acceptor for synthesis of exciplex(Acceptor).We apply 1,3,5-tri(9H-carbazol-9-yl)benzene,1,3,5-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)benzene as donor(Donor),1,3,5-tri(1H-indol-1-yl)benzene and Bphen for acceptors,1,3,5-tri(9H-carbazol-9-yl)benzene and Bphen in 1:1 quantities were synthesized,respectively 1,3,5-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)benzene and Bphen,and 1,3,5-tris(3,6-ditert-butyl-9H-carbazol-9-yl)benzene and 1,3,5-tri(1H-indol-1-yl)benzene.The optical properties of electrochemical ere analyzed.The strong absorption peaks of the UV-vis absorption spectra of the three compounds in different solvents were located at 260,260,295 nm respectively.The maximum wavelength of fluorescence emission peak in different solvents is between 346-378 nm,and redshift occurs with the increase of solution polarity.The emission spectra of the donor-recipient mixture are redshifted compared to those of the donor and recipient themselves,indicating the formation of an exciplex.The maximum fluorescence quantum efficiency is 7.6%(in n-hexane)of 1,3,5-tri(3,6-di-tert-butyl-9H-carbazol-9-yl)benzene and Bphen.In addition to the 1:1 substance amount complex,we also tested the fluorescence spectra of other substance ratio complexes in dichloromethane solution,where substance amount 1:2 and substance amount 2:1,1,3,5-tri(3,6-di-tert-butyl-9H-carbazol-9-yl)benzene comlex with 1,3,5-tri(1H-indol-1-yl)benzene,substance quantities 1:2,substance quantities 1:1 and substance quantities 2:1.The fluorescence spectra of 1,3,5-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)benzene and Bphen complexes showed a red shift compared with that of both donor and recipient,indicating the formation of different exciplex.In dichloromethane solution,1,3,5-tri(9H-carbazol-9-yl)benzene and Bphen complex had the highest fluorescence quantum efficiency,up to 4.2%.