Synthesis And Luminescent Performances Of Ir-Complexes With Triarylamine-based Picolinic Acid Derivatives

The molecular designs and synthesis of triarylamine-based picolinic acid derivatives used as ancillary ligands, and their cyclometalated iridium complexes used as red-and green-emitters, as well as optoelectronics properites of these compounds were investigated in order to solve current problems of organic/polymeric electroluminescent materials and devices. The studies contain the following works: (1) Three compounds of triarylamine-based picolinic acid derivatives used as ancillary ligands were designed and synthesized; (2) Two kinds of cyclometalated iridium complexes used as red- and green-emitters, which contain triarylamine-based picolinic acid derivatives, were achieved; (3) The influence of the molecular structures of the ancillary ligands of triarylamine-based picolinic acid derivatives on UV and PL performances of their cyclometalated Ir-complexes were studied; (4) Polymeric light-emitting devices(PLEDs) were fabricated using these cyclometalated complexes as guest and a blend of polyfluorene (PFO) and oxadiazole derivative(PBD) as host matrix. The influence of molecular structures of these ancillary ligands of triarylamine-based picolinic acid derivatives and cyclometalated iridium complexes and polymeric host materials on the electrophosphorescent properties of the devices were studied. The PLEDs display a maximum external quantum efficiency(QEext) of 10.15% and a current efficiency of 8.46 cd/A.The results revealed as follows: (1) The molecular structures of these ancillary ligands of triarylamine-based picolinic acid derivatives are an important factor to affect the luminescent performance of the cyclometalated iridium complexes. The cyclometalated iridium complexes (Piq)₂Ir(TPAPic)- , (Piq)₂Ir(MeTPAPic)- and (Piq)₂Ir(MeOTPAPic)-doped PLEDs exhibited a maximum QEext of 10.15%, 8.2% and 9.97% respectively, while the cyclometalated iridium complexes (Piq)₂Ir(Pic) doped PLEDs displayed a QEext of 7.06%. This indicates that incorporating triarylamine-based picolinic acid derivatives into the cyclometalated iridium complexes can help to improve the photoelectric performances of the devices and increase luminescence efficiency as well. (2) When the iridium complexes with triarylamine-based picolinic acid derivatives were introduced into the cyclometalated iridium complexes, iridium complexes display the enhanced transition absorption of metal-ligand charge transition(MLCT), which resulted in promoting high-efficiency energy transfer from the host to the guest. (3) The cyclometalated iridium complexes (Piq)₂Ir(TPAPic)- , (Piq)₂Ir(MeTPAPic)-, (Piq)₂Ir(MeOTPAPic)-and (Piq)₂Ir(Pic)- doped PFO-PBD devices, exhibited similar electroluminescent spectra with emissions peaked at 610 nm. This implied that the cyclometalated ligands have dominated the color in the red-emitting iridium complexes. (4) Compared with the iridium complexes FIr(Pic), the Ir-complexes using triarylamine-based picolinic acid derivatives as ancillary ligands and 2-(2,4-difluorophenyl)pyridine as a cyclometalating ligand, displayed red-shifted photoluminescent emission. This phenomenon indicates that the ancillary ligands have sometime influence on the emission of their cyclometalated iridium complexes.