Synthesis and properties of new electroluminescent materials

Abstract

New EL polymers possessing both hole and electron transporting units in the main chain are synthesized. The polymer prepared by palladium catalyzed Heck reaction of 3,5-bis-(4-bromophenyl)-4-phenyl-[1,2,4]triazole and [4-(2-ethylhexyloxy)-phenyl]-bis-(4’-vinylphenyl)amine show a large weight average molecular weight (Mw) (25,000) and small polydispersity index (PDI) (1.2). The oligomers synthesized by Wittig condensation have $M_w$ of 4,000 and PDI of 1.8. All the polymer and oligomers synthesized exhibit remarkable thermal stability with high decomposition temperature and high $T_g$ as determined by TGA and DSC under nitrogen atmosphere. The EL emission maximum peaks of the materials prepared are in the range of 535nm~560nm corresponding to green~yellowish-green. Among the three hole-blocking/electron transporting moieties, the 1,3,4-oxadiazole unit shows the best electron injection and transporting property. We synthesized a series of bis [N-(p-X-phenyl) salicylaldiminato] zinc(II) and investigated their absorption, photoluminescence (PL) and electroluminescence (EL) properties. The p-substituted ligands Zn complex showed large bathochromic shift in introducing EWG on p-position which cause a lowering of the LUMO energy and blue-shift in EDG substituted complex, compared to unsubstituted ligand Zn complex. The p-substituted ligands Zn complexes result in decrease of electroluminescent efficiency and devices made with these materials have a higher operating voltage compared to device based on unsubstituted ligand Zn complex.