Synthesis And Photoelectric Properties Of Fluorinated Phenylimidazothiazole Cyclometallated Iridium(?) Complexes

In this paper,thiourea,acetone and different fluorobenzoyl bromides(3,5-difluorobenzoyl bromide,3,4,5-trifluorobenzoyl bromide,2,3,4,5-tetrafluorobenzoyl bromide and 3,5-bistrifluoromethyl benzoyl bromide)were reacted to prepare four new cyclometallated ligands:4-3',5'-difluorophenyl-7-methylimidazo[2,1-b]thiazole(mdfpit),4-3',4',5'-trifluorophenyl-7-methylimidazo[2,1-b]thiazole(mtfpit),4-2',3',4',5'-tetrafluorophenyl-7-methylimidazo[2,1-b]thiazole(mffpit)and 4-(3',5'-bistrifluoromethyl)phenyl-7-methylimidazo[2,1-b]thiazole(mtfmpit).These were used as cyclometallated ligands to synthesize twenty phosphorescent iridium(?)complexes with methyl 2-pyridinecarboxylic acid(pic),isoquinolinecarboxylic acid(3-IQA),quinaldic acid(2-QA),2-(pyridin-2-yl)phenol(2-ylppy),2-(2,4-difluorophenyl)pyridine(dfppy),and pyridine-2-sulfonic acid(2-sappy)as auxiliary ligands.Their synthetic route,thermogravimetric stability,optoelectronic properties,and LED performance have been researched,to further compare the effects of introducing-F atoms and-CF₃groups at different positions on the benzene ring of the cyclometallated ligand.When different numbers of-F atoms are introduced into the benzene ring of the cyclometallated ligand,the thermal stability of the iridium(?)complexes are improved,which is beneficial to the preparation of LED devices,and the photoluminescence quantum yield(PLQY)has significantly improved,which is beneficial to promote the luminous efficiency of LED devices.And the LUMO energy level rises,which makes the photoluminescence emission spectrum are blue-shifedt,and the maximum emission wavelengths are 517 nm-618 nm,covering the emission of green to red light region.When the 3?,5?-H atoms on the benzene ring of the cyclometallated ligands are replaced by the-CF₃groups,the solubility of the iridium(?)complexes are improved,and the PLQY has increased relative to the introduction of the-F atoms at the 3?,5?position,the HOMO/LUMO energy level decreases,and the photoluminescence spectrum continues to blue-shifted.Among them,(mtfpit)₂Ir(dfppy)has good thermal stability,485?T_b;(mtfpit)₂Ir(pic)and(mffpit)₂Ir(pic)has maximum emission wavelengths of 535 nm and 525 nm,and PLQY were 58.4%and 61.1%.The higher quantum yield is helpful to the development and utilization of luminescent materials.The iridium(?)complexes with mffpit as the cyclometallated ligand has excellent thermal stability and PLQY.Using the synthesized iridium(?)complexes as emitters,LED chips based on In Ga N chip excitation were developed,which showed good performances.Among all LED,the luminous efficiency of the(mdfpmt)₂Ir(2-QA)based LED is 3.41 lm/W with CIE coordinate of(0.60,0.38),which are very similar to the saturated standard red light emission,and is prepared as a red-orange LED device;the(mtfpit)₂Ir(pic)LED device has a luminous efficiency of 17.11 lm/W,which is developed as a highly efficient and stable green LED material.The results prove the potential of the studied iridium(?)complexes as a candidate for LED materials,but the LED devices with mffpit and mtfmpit as cyclometallated ligands have poor luminous efficiency and color purity.Finally,when the-F atoms or-CF₃groups are introduced into the benzene ring of the cyclometallated ligands,the luminescence color of the iridium(?)complexes are adjustable,and the PLQY of the iridium(?)complexes and the luminous efficiency of the LED are changed.