Syntheses And Properties Of New Phosphorescent Complexes And Hole Transport Materials

Organic light-emitting diodes (OLEDs) have fueled active research due to their applications in high-resolution, full-color, flat-panel displays and lighting sources. The OLEDs based on phosphorescent materials show remarkable performance due to the use of both singlet and triplet excitons caused by strong spin-orbital coupling in the existence of heavy metal atoms, and exhibit higher internal quantum efficiency up to 100% in priciple. Thus, heavy metal complex such as rhenium(I), ruthenium(II) and iridium(III) complexes have been extensively studied as electrophosphorescent materials. Besides, carrier transport materials play important roles in improving the performances of the OLEDs. In this dissertation, we reported the syntheses and photophysical properties of new Re(I), Ru(II) and Ir(?) complexes and two novel hole transport materials. Highly efficient OLEDs based on the Ir(III) complexes and hole transport materials were fabricated and studied.1. Three N, N-bidentate ligands,5,5'-dibromo-2,2'-bipyridine (L1) and two hole-transporting carbazole containing ligands of 5-bromo-5'-carbazoly 1-2,2'-bipyridine (L2),5,5'-dicarbazolyl-2,2'-bipyridine (L3), and their corresponding Re(CO)3ClL complexes (ReLl-ReL3) have been successfully synthesized and characterized. In the UV-vis spectra, all complexes display intense absorption bands at ca.220-350nm assigned to spin-allowed intraligand (???*) transitions, and the low energy broad bands in the 360-480nm region are attributed to the metal to ligand charge-transfer d?(Re)??*(diimine) (MLCT). Upon the excitation on the peak maxima, all complexes show strong MLCT phosphorescence emission around 620nm. The absorption and emission intensities can be enhanced by the introduction of carbazole moieties, and the complex ReL3 shows two times higher luminescence quantum efficiency than that of complex ReLl. The appended carbazole moieties, which widen the absorption profile and act as light-harvesting units, are expected to improve the hole-transporting ability of the Re(I) complex and obtain high efficient OLEDs.2. Four 2,2'-bipyridine derivatives containing electron-transporting oxadiazole moieties at different positions,4,4'-bis(5-phenyl-[1,3,4]oxadiazol-2-yl)-2,2'-bipyridine (L4),4,4'-bis[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-2,2'-bipyridine (L5),5,5'-bis(5-phenyl-[1,3,4]oxadiazol-2-yl)-2,2'-bipyridine (L6), and 5,5'-bis[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-2,2'-bipyridine (L7), and their corresponding Re(CO)3ClL complexes (ReL4-ReL7) have been synthesized and characterized. All the complexes except for ReL7 show efficient phosphorescence emission. The strongest phosphorescence emission is observed in complex ReL4 due to the introduction of oxadiazole moieties at 4,4'-positions of bipyridine. Moreover, the complexes ReL4 and ReL5 of 4,4'-disubsituted by oxadiazole moieties exhibit much better luminescence than that of ReL6 and ReL7 which are 5,5'-disubsitution complexes by the same groups, respectively. These observations imply that the modification of some bipyridine Re(I) carbonyl complexes with suitable electron-withdrawing moieties at 4,4'-positions of bipyridine would produce efficient phosphorescent materials.3. Six Ru(II) complexes (Rul-Ru6) with the type of [Ru(bpy>2L]X2 (Rul-Ru3:L= L1-L3, X=Cl"; Ru4-Ru-:L=L1-L3, X=PF6-) were synthesized based on 2,2'-bipyridine and their derivatives L1, L2 and L3. Their photophysical properties and electrochemiluminescence (ECL) properties were investigated in detail. All complexes Rul-Ru6 show strong absorption in UV-vis region and exhibit typical MLCT emission of Ru(II) polypyridyl complexes. The introduction of carbazole moieties improves the MLCT absorption and emission intensity like the Re(I) complexes. Moreover, the Ru(II) complexes Rul-Ru6 exhibit good electrochemiluminescence (ECL) properties in [Ru(bpy)2L]2+/tri-n-propylamine (TPA) acetonitrile solution and the complexes with PF6- show higher ECL emission intensity than that of the complexes with Cl" based on the same ligands.4. New Ir(III) complexes Ir(tfmppy)2(tfmtpip)(Irl) and Ir(tfmpiq)2(tfmtpip)(Ir2) (tfmppy=4-trifluoromethylphenylpyridine, tfmpiq=1-(4-trifluoromethylpheny)-isoquinoline, tfintpip=tetra-(4-trifluoromethylpheny)limidodiphosphinate) have been successfully synthesized and characterized. OLEDs in the configuration ITO /TAPC (40 nm)/Irl or Ir2 (x wt%):mCP (20 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al (100 nm) have been fabricated. A maximum power efficiency (?p,max) of 113.23 lm W-1, a maximum current efficiency (?c, max) of 115.39 cd A-1 and a maximum luminance (Lmax) of 49273 cd m-2 at 12.0 V are achieved for the OLEDs based on complex Irl. To the best of our knowledge, this is one of the best performances for Ir(III) complex based OLEDs in the light-green-emitting region.5. Two hole transport materials (CPNA1 and CPNA2) were prepared with novel structures by the integration of carbazole moieties and the dimer or trimer of N-phenyl-1-naphthylamine through the phenyl ring. OLEDs in the configuration ITO/CPNA1 or CPNA2 (40 nm)/Ir1 (6 wt%):mCP (20 nm)/TmPyPB (40 nm) /LiF (1nm)/A1 (100nm) (named HG1 and HG2, repectively) have been fabricated. The performances of the device HG1 using CPNA1 as hole transport material are quite encouraging, with a ?p,max of 89.58 lm W-1, a ?c,max of 99.85 cd A-1 and a Lmax of 47873 cd m-2 at 13.2 V. The device HG1 is also among one of the highest efficient green ones that are known to date.