Seung-Yong Song

Synthesis and electroluminescence properties of ortho-, meta- and para-linked polymers containing oxadiazole unit

A series of electroluminescent π-conjugated polymers containing an oxadiazole group in the backbone was prepared through Hecks coupling or Wittigs condensation reaction, 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-phenylenevinylene] (PMOXPV) and poly[(2,5-diphenyl-1,3,4-oxadiazole)-2,4-diylvinylene-alt-1,4-(2,5-dihexyloxy)-phenylenevinylene] (PPOXPV). The three polymers were soluble in common organic solvents and showed good thermal stability. The maximum photoluminescence (PL) wavelengths of POOXPV, PMOXPV and PPOXPV appeared at 495, 470, and 510 nm, respectively. The electroluminescence (EL) spectra of POOXPV and PPOXPV showed maximum peaks at 500 and 510 nm, respectively, corresponding to greenish-blue light, with the single-layer light-emitting diodes of Al/polymer/ITO glass fabricated. In blending synthesized polymers with 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM), polymers are also believed to serve as an excellent polymer electron-transporting materials in our devices.

Synthesis and LED device properties of carbazole and naphthalene contained conjugated polymers

Abstract Two new fully conjugated alternating copolymers containing both carbazole and naphthalene units were prepared through the Wittig condensation polymerization (carbazole units were linked with napthalene units by 1,4- and 2,6-linkages). The maximum photoluminescence wavelengths of 2,6-PNCPV and 1,4-PNCPV were found at 498 and 545 nm, which correspond to the greenish–blue and the yellow emission region, respectively, depending on the napthalene linkage. The turn-on voltages of 2,6-PNCPV and 1,4-PNCPV were 10.4 and 9.6 V, respectively, when the single-layer light-emitting diodes of Al/2,6-PNCPV or 1,4-PNCPV/ITO glass were fabricated. The electroluminescence spectrum of 1,4-PNCPV exhibited EL emissive band at 553 nm (yellow emission). Interestingly, the EL spectrum of 2,6-PNCPV was tailed to the longer wavelength region from the EL maximum point of 496 nm, which may be caused by formation of the intermolecular excimers. The emission color of 2,6-PNCPV was almost white to the naked eyes due to the tailing of 2,6-PNCPV emission and the weak interchain excimer peak at 750 nm.

New soluble light-emitting diode polymer containing oxadiazole unit

Abstract A new light emitting (LED) polymer (POOXPV) with oxadiazole unit has been prepared and characterized by UV-visible and photoluminescence (PL) spectroscopy. This polymer is soluble in common organic solvents and has good thermal stability up to ca. 400 °C. The UV absorption and PL emission maxima were 360 nm and about 500 nm, respectively. In order to investigate electron transporting property, the polymer was blended with poly[2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylenevinylene] (MEH-PPV). The device showed bright orange-red color and enhanced EL power relative to that of MEH-PPV.

New orange-red light emitting diode from poly[2-(5-cyclo-hexylmethoxypentyloxy)-5-methoxy-1,4-phenylenevinylene]

Poly[2-(5-cyclohexylmethoxypentyloxy)-5-methoxy-1,4-phenylenevinylene] (PMCYHPV) was synthesized through dehydrohalogenation polymerization. This polymer shows good solubility in common organic solvents. The absorption and photoluminescence (PL) emission maxima of PMCYHPV are 497 nm and 590 nm, respectively. The electroluminescence (EL) properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and PMCYHPV were studied by means of the EL spectra, current-voltage characteristics, and EL power-current characteristics. The measured relative EL quantum efficiency of PMCYHPV is about 6 times higher than that of MEH-PPV. The EL enhancement of PMCYHPV originates from the reduction of non-radiative decay of excitons caused by better separation of the polymer chains due to the rigid cyclohexyl side group. Furthermore, we found that the PL quantum efficiency of PMCYHPV is 15% higher than that of MEH-PPV.

The enhancement of electroluminescence efficiency by molecular doping

Abstract We report on the investigation of electroluminescence (EL) for a dye-doped polymer. This doping system consists of main chain conjugated poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and highly fluorescent dye rubrene. We fabricated many EL samples of various doping ratios due to the good solubility of rubrene and MEH-PPV in organic solvents. Low operation voltage and high EL efficiency were obtained simultaneously in the molecularly doped system. We made EL cells having an emission efficiency 10 times higher than that of an undoped MEH-PPV diode with nearly the same turn-on voltage.

Synthesis and properties of new light-emitting polymers containing fluorinated tetraphenyl units

A series of fully conjugated blue light-emitting polymers has been synthesized. The polymers are composed of fluorinated tetraphenyl units, and dialkoxybenzene, carbazole and fluorene containing arylenevinylene units. The synthesized polymers were soluble in common organic solvents and thermally stable up to 300°C. The photoluminescence (PL) peak wavelengths of the polymers were varied from 490 to 468 nm, depending on the polymer structure. Single-layer EL devices using the polymers were fabricated. Light emission from the devices becomes visible between 12 and 22 V, depending on the device structure.

Efficient and blue light-emitting polymers composed of conjugated main chain

Abstract Poly[ o ( m,p )-phenylenevinylene- alt -2,5-bis(trimethylsilyl)- p -phenylenevinylene], o ( m,p )-PBTMS-PPV and related derivatives were prepared and their light-emitting properties were studied. The peaks of the photoluminescence spectra of p -PBTMS-PPV, o -PBTMS-PPV, and m -PBTMS-PPV were at 485, 470, and 440, respectively. New, fully conjugated polymers composed of both electron-transporting oxadiazole and hole-transporting carbazole moieties PPOX-CAR and PMOX-CAR were also prepared. The electroluminescence peaks of those polymers occurred at 495 and 450 nm, respectively. The maximum brightness of Al/PPOX-CAR/ITO single layer device was 500 cd/m 2 at 20 V.

Synthesis of poly(phenylene-alt-thiophene) polymer and characterization of its light emitting properties

A new fully conjugated light-emitting polymer based on phenylene-alt-thiophene backbone has been synthesized by utilizing the Stille coupling reaction. The synthesized polymer was soluble in common organic solvents such as chloroform, THF, 1,2-dichloroethane, and has good film property. The maximum photoluminescence (PL) and electroluminescence (EL) peak wavelengths of the polymer were 530 and 520 nm, respectively, in green light emission region. The turn-on voltage of polymer appeared at 9.5 V in indium tin oxide (ITO)/polymer/Al device fabrication. In this presentation, synthesis and EL properties of the polyphenylene-alt-thiophene polymer will be discussed.