High-Efficiency Poly(p-phenylenevinylene)-Based Copolymers Containing an Oxadiazole Pendant Group for Light-Emitting Diodes

Abstract

A new series of high brightness and luminance efficient poly(p-phenylenevinylene) (PPV)-based electroluminescent (EL) polymers, poly[2-[4-[5-(4-(3,7-dimethyloctyloxy)phenyl)-1,3,4-oxadiazole-2-yl]phenyloxy]-1,4-phenylenevinylene] (Oxa-PPV), poly[2-[2-((3,7-dimethyloctyl)oxy)phenoxy]-1,4-phenylenevinylene] (DMOP-PPV), and their corresponding random copolymers, poly[[2-[4-[5-(4-(3,7-dimethyloctyloxy)phenyl)-1,3,4-oxadiazole-2-yl]phenyloxy]-1,4-phenylenevinylene]-co-[2-[2-((3,7-dimethyloctyl)oxy) phenoxy]-1,4-phenylenevinylene]] (Oxa-PPV-co-DMOP-PPV), with an electron-deficient 1,3,4-oxadiazole unit on the side groups, were synthesized through the Gilch polymerization method. The newly designed and synthesized asymmetric molecular structures of Oxa-PPV, DMOP-PPV, and Oxa-PPV-co-DMOP-PPV were completely soluble in common organic solvents, and defect-free optical thin film was easily spin-coated onto the indium tin oxide (ITO) substrate. Oxa-PPV shows a high glass transition temperature (T(g)), which might be an advantage for long time operation of polymer light-emitting diodes (PLEDs). Double-layer LEDs with an ITO/PEDOT/polymer/Al configuration were fabricated by using those polymers. Electrooptical properties and device performance could be adjusted by introducing the Oxa-PPV content in the copolymers. The emission colors could be tuned from green to yellowish-orange via intramolecular energy transfer. The improved device performance of Oxa-PPV over DMOP-PPV and Oxa-PPV-co-DMOP-PPV may be due to better electron injection and charge balance between holes and electrons and also efficient intramolecular energy transfer from 1,3,4-oxadiazole units to PPV backbones. The maximum brightness and the luminance efficiency of Oxa-PPV were up to 19395 cd/m(2) at 14 V and 21.1 cd/A at 5930 cd/m(2). The maximum luminance efficiency of Oxa-PPV is ranked the highest value among the PPV derivatives to date.

Synthesis and Characterization of Novel Conjugated Polymer with 4H-Cyclopenta[def]phenanthrene and the Sulfanyl Group

“…The oxidation potential is derived from the onset of electrochemical p-doping, and HOMO level was calculated according to the empirical formula (E HOMO ¼ Àð½E onset ox þ 4:8Þ) (eV). 17 In the anodic scan, the onset of oxidation of PCPP-MSC occurred at 0.85 V (vs. SCE), which corresponded to the ionization potential (I p ) value of À5:65 eV. The absorption onset wavelength of PCPP-MSC was observed at 454 nm for the solid thin film, corresponding to band gap of 2.73 eV.…”

Charge-Transporting Polymers

“…Figure 2 shows several examples of main-chain p-conjugated copolymers for OLEDs. Main-chain p-conjugated polymers containing p-electron skeletons as side groups, e.g., PPVs having side groups of oxadiazoles, have also been developed [7,8,22].…”

Synthesis and Characterization of a Water-Soluble Ionic Polyacetylene Derivative

“…Thereby, these materials are important as the active materials in a new generation of electronic and optical devices, including light-emitting devices [15,[19][20][21], photovoltaic cells [22,23], biological and chemical sensors [24,25], photo-detectors [26], optical lasers [27], field-effect transistors [28], and nonvolatile memory devices [29,30].…”