Synthesis And Properties Study Of 1,3,4-oxadiazole And Thiadiazole-2-thiol Derivatives And Their Cyclometaled Platinum Complexes

Organic electrophosphorescent materials are one of prime focuses of organic light-emitting device in recent years due to their high-efficiency emission utilizing both singlet and triplet excitions. Most of the reported organic electrophosphorescent materials were mononuclear heteroleptic cyclometalated complexes. However, a few dinuclear heteroleptic cyclometalated complexes has been reported. In order to study the relationship between luminescent properties and dinuclear heteroleptic cyclo- metalated complexes, as well as to obtain high-efficiency dinuclear heteroleptic cyclometalated complexes and their polymer light-emitting devices (PLEDs), a series of anionic ancillary ligands of 2-aryl-2-thiol-1,3,4-oxadiazole, 2,5-dithiol-1,3,4- thiadiazole derivates and their dinuclear platinum complexes were synthesized. The PLEDs with these platinum complexes were fabricated. The key studies are listed below.1. A series of anionic ancillary ligands of 2-aryl-5-thiol-1,3,4-oxadiazole (Cn-OXT), 2,5-dithiol-1,3,4-thiadiazole (TX2T) derivates and their dinuclear platinum complexes was obtained. These dinuclear platinum complexes contain CnFPt, CnPtpiq and FPt2(FIrPic-C8-TX2T)2 in which FPt is [4,6-diflurophenyl- pyridine-N,C2] platinum(Ⅱ), Ptpiq is [1-phenyliso-quinoline-N,C2'] platinum(Ⅱ) and FirPic-C8-TX2T is anionic ancillary ligands of 2,5-dithiol-1,3,4-thiadiazole derivatives containing di (4,6-diflurophenylpyridine-N,C2) (picolinate-O,N) iridium(II) chromophore connected with alkoxy group, n is carbon number in alkoxy group (n =0, 6, 8, 12, 16). These compounds were characterized by NMR.2. The UV absorption and photoluminscence properties of these ancillary ligands of Cn-OXT, FIrPic-C8-TX2T and their dinuclear platinum complexes, as well as the influence of the ancillary ligands on the optoelectronic properties of their dinuclear platinum complexes were studied. These dinuclear platinum complexes exhibited obvious UV-vis absoption from metal-metal-ligand charge transfer and intense photoluminescence with red and infrared emission, in which the CnFPt and CnPtpiq complexes displayed a maximum photoluminescent peak at 621 nm and 720 nm, respectively.3. The influence of ancillary ligands of Cn-OXT and FIrPic-C8-TX2T on the electrochemical properties of these dinuclear platinum complexes were investigated by cyclic voltammetry. It is benefit to select polymer host matrix which has a matched energy level with dinuclear platinum complexes.4. The thermal properties of these dinuclear platinum complexes were also studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that these dinuclear platinum complexes presented excellent thermo-stability.5. PLEDs were made using these dinuclear cyclometalated platinum complexes as dopant and a blend of poly(vinylcarbazole) (PVK) and 2-tert-butylphenyl-5- biphenyl-1,3,4-oxadiazoles (PBD) or a blend of poly(9,9-dioctylfluorene) (PFO) and PBD as host matrix. Their electroluminescence properties were studied. The results are shown below. (1) PLEDs using PFO-PBD as host matrix presented better device performances than PLEDs using PVK-PBD as host matrix. (2) A turn-on voltage of 6.75 V and a maximum external quantum efficiency of 8.5% (at 241 cd/m2) and a peak brightness of 3229 cd/m2 (at 17 V), as well as CIE coordination (0.59, 0.40) were achieved in the PLEDs using PFO-PBD as host matrix at 8% C8FPt doping concentration. To the best of our knowledge, these are the highest efficiencies for the binuclear Pt (II) complexes-doped PLEDs with red emissions. (3) A turn-on voltage of 9.75 V and a maximum external quantum efficiency of 6.4% (at 275 cd/m2) and a peak brightness of 3229 cd/m2 (at 22.25 V), as well as CIE coordination (0.68, 0.31) were achieved in the PLEDs using PFO-PBD as host matrix at 8% C8Ptpiq doping concentration. It implies that CnPtpiq displayed high-efficiency near-infrared emission in the PLEDs. To the best of our knowledge, these are the highest efficiencies for the binuclear Pt (II) complexes-doped PLEDs with near-infrared emissions. (4) FPt2(FIrPic- C8-TX2T)2 exhibited white emission in the devices using PVK-PBD as host matrix at below 2% dopant concentration under various voltages.It is interesting to further develop dinuclear platinum complexes and their application in red-, near-infrared and white-emiting PLEDs.