Synthesis And Properties Of Phosphorescent And Host Materials With Triphenylamine Groups

OLEDs(Organic Light-emitting Diodes)have attracted a lot of attention in the field of lighting and display because of their fast response,low turn-on voltage,flexible display,low cost and thin panel.Fluorescent materials and phosphorescent materials constitute OLED electroluminescent materials.Endowed with the capability to harvest both singlet excitons(25 %)and triplet excitons(75 %),phosphorescent OLEDs with phosphorescent materials have attracted considerable interests because of the demonstrated potential for achieving internal quantum efficiency of 100 %.Among them,iridium(III)complexes have been considered as the most promising phosphorescent materials owe to their short lifetimes and high luminous efficiencies.However,they have to suffer from concentration quenching and triplet-triplet annihilation,which resulted in low efficiencies of devices.Therefore,in order to improve phosphorescent OLEDs with high efficiencies,the development of phosphorescent and host materials is of great importance.The compound triphenylamine has been widely used in OLEDs,due to high triplet energy level,better thermal stability and hole transporting ability.Using the above characteristics of triphenylamine,for one thing,a series of iridium complexes were synthesized through modification of ligands of iridium complexes and changing conjugation of ligands;for another,a bipolar phosphorescent host material with triphenyl group was synthesized.This work is study of the relationship between these compounds structures and properties.Based on mentioned above,we have done the following work:In the first part of this paper,the carbazole group was injected in 4-position of 2-(2’,4’-difluorophenyl)pyridine,and tert-butyl,one or two triphenylamine group was substituted in 3-or 6-position of carbazole to obtain a series of hole-transport iridium complexes,T0,T1 and T2.The structures of compound were verified by 1H NMR,13 C NMR and mass spectroscopy.TGA and DSC were used to measure the thermal stability of T0,T1 and T2.Their results showed that the glass transition temperatures(Tg)of T0,T1 and T2 were 119 oC,229 oC,101 oC,and thermal decompositiontemperatures(Td)were 391 oC,277 oC,140 oC,respectively.The electrochemical properties of T0,T1 and T2 were studied by cyclic voltammetry.The HOMO levels of T0,T1 and T2 were estimated to be-5.49 eV,-5.49 eV,-5.44 eV,and the LUMO energy levels were calculated to be-2.47 eV,-2.55 eV,-2.63 eV.The HOMO level of T2 is very close to the HOMO level of PEDOT: PSS(-5.20 eV),indicating that the dendritic iridium complex T2 has better hole transport ability.Single-layer Device A,B and C were made by T0,T1 and T2,respectively.Device C,which was based on iridium complex T2 with two triphenylamine groups,showed best EL performance.The current efficiency was 16.68 cd/A and power efficiency was 5.65 lm/W.In the second part of this paper,a bipolar phosphorescent host material BFB-TPA was designed and synthesized,carrying triphenylamine as the electron donor and benzofurylidene as the electron acceptor.And the structures of BFB-TPA were verified by 1H NMR,13 C NMR and mass spectra.The thermal stability of BFB-TPA was studied by TGA,and BFP-TPA showed Td(5 % weight loss)around323 oC.The electrochemical properties of BFB-TPA were studied by cyclic voltammetry.The HOMO energy level was estimated to be-5.42 eV,the LUMO energy level was calculated to be-2.20 eV.The HOMO energy level of BFB-TPA is very close to that of PEDOT: PSS(-5.2 eV),and the LUMO level of BFP-TPA is similar to that of LiF/Al(-2.9 eV).Therefore,BFB-TPA is a good bipolar host material.BFP-TPA based Device L,M and N were doped with green,red and blue fluorescent guest materials.Device L showed the best EL performance.The current efficiency was 15.35 cd/A and power efficiency was 5.38 lm/W.