Synthesis and characterization of organic light-emitting polymers

Abstract

We investigated electroluminescent (EL) characteristics of polymer and low molecular organic light emitting diodes. We synthesized new polymers and low molecular organic light emitting material containing oxadiazole unit or bis-styryl units. The synthesized polymers and low molecular organic light emitting material were soluble in common organic solvents and showed good thermal stability. A series of electroluminescent π-conjugated polymers containing an oxadiazole group in the backbone, poly[(2,5-bis(5-hexyloxyphenyl)-1,3,4-oxadiazole)-2,2-diylvinylene-alt-1,4-phenylenevinylene] (POOXPV), poly[(2,5-bis(2-hexyloxyphenyl)-1,3,4-oxadiazole)-5,5-diylvinylene-alt-1,4-phenylenevin-ylene] (PMOXPV) and poly[(2,5-diphenyl-1,3,4-oxadiazole)-2,4-diylvinylene-alt-1,4-(2,5-dihexyloxy)-phenylenevinylene] (PPOXPV), were prepared through Heck’s coupling or Wittig’s condensation reaction. The maximum photoluminescence (PL) wavelengths of POOXPV, PMOXPV and PPOXPV appeared at 495 nm, 470 nm, and 510 nm, respectively. The electroluminescence (EL) spectra of POOXPV and PPOXPV showed maximum peaks at 500 nm and 510 nm, respectively, corresponding to greenish-blue light, with the single-layer light-emitting diodes of Al/polymer/ITO glass fabricated. To obtain high intense emissive light devices and to investigate electron-transporting ability, the POOXPV was blended with poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamin)styryl]-4H-pyran (DCM). The maximum brightness of the Al/(MEH-PPV/POOXPV=1:5)/ITO single-layer device was 2,400 cd/㎡. And compared with 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) (well known as electron-transporting material), synthesized polymers are also believed to serve as an excellent polymer electron-transporting materials in our devices. We also synthesized two new fully conjugated alternating copolymers containing both oxadiazole and carbazole (or fluorene) units throug...