Sung Ouk Jung

Highly efficient orange organic light-emitting diodes using a novel iridium complex with imide group-containing ligands

We report the synthesis and device characterization of a novel iridium complex using a phenylpyridine derivative containing an imide functional group as a bis-cyclometallized ligand ((impy)2Ir(acac)) for orange organic light-emitting diodes (OLEDs). The photoluminescence of the dopant emits orange light with the main peak of 560 nm and a shoulder of 595 nm. The OLEDs made with the synthesized dopant also produce intense orange electroluminescence at 568–572 nm wavelengths depending on the device geometry. Very high peak external quantum efficiencies of 13.8–14.4%, peak power efficiencies of 29.2–32.7 lm/W, and low operation voltages of 5.3–5.4 V at 1000 cd/m2 have been demonstrated for the orange OLEDs.

Synthesis and Characterization of Organic Light-Emitting Copolymers Containing Naphthalene

Conjugated PPV-derived block copolymers containing 2-ethylhexyloxynaphthalene unit were synthesized and characterized in this study. The resulting polymers were soluble in common organic solvents and showed good thermal stabilities. The weight-average molecular weights (Mw) of the copolymers ranged from 246,000 to 475,000 with PDIs of 1.3∼2.1. The optical properties of these polymers, measured both in a chloroform solution and on a film, showed a maximum absorption at 405∼476 nm for Copolymers I∼VIII. In the PL spectra, Copolymers I∼VIII showed maximum peaks at 510∼566 nm. The HOMOs, LUMOs and band gaps of the PPV derivatives of Copolymers I∼VIII were 5.30∼5.77, 3.04∼3.24, and 2.5∼2.2 eV, respectively. The multi-layered, light-emitting diodes of ITO/PEDOT/copolymers/LiF/Al exhibited turn-on voltages of 6∼2.5 V. Copolymer VIII exhibited the maximum brightness of 3,657 cd/m2. Particularly, Copolymer VII, with an identical composition of MEH-PPV and naphthalene-PPV, showed a maximum luminance efficiency and power efficiency of 2.63 cd/A and 1.06 lm/W, respectively.

Efficient and colour-stable hybrid white organic light-emitting diodes utilizing electron―hole balanced spacers

High-efficiency two-colour white organic light-emitting diodes (WOLEDs) comprising a newly synthesized iridium complex orange phosphor ((impy)2Ir(acac)) and a blue fluorophor (BD012) have been realized by placing several kinds of thin spacers between two emitters. Hybrid WOLEDs with a spacer composed of a hole-transporting N,N-dicarbazolyl-3,5-benzene (mCP) and an electron-transporting 4,7-diphenyl-1,10-phenanthroline (Bphen) exhibit a high external quantum efficiency (EQE) of up to 8.4% and a negligible colour change (the colour coordinate of (0.39, 0.41) at 1000 cd m−2) with increasing brightness, whereas the device using a hole-transporting mCP spacer shows a relatively low EQE of 6.2% and a large shift of emitting colour with increasing brightness. Device performance is further characterized based on the charge transport behaviour of the spacers inserted between the two emitters.

Effective Electrophosphorescence Emitting Devices by Using New Type Ir(III) Complex with Bluky Substistuent Spacers

The new green Ir(III) complex, fac-tris[4-methyl-2-(4′-trimethylsilylph-enyl)pyridine] [Ir(msippy)3], is synthesized and phosphorescent light emitting devices fabricated by using them as triplet emissive dopants. Ir(dsippy)3 in UV-Vis. spectra showed absorption band at 395 nm originating from 1MLCT. The EL devices with configuration of ITO/CuPc (10 nm)/α -NPD (40 nm)/CBP-Ir(msippy)3 (20 nm)/BCP (10 nm)/Alq3 (40 nm)/LiF (1 nm)/Al (100 nm).showed the emission maximum at 516 nm, due to the radiative decay from 3MLCT state to ground state. The 6% doped devices showed the maximum efficiency of 49.9 cd/A and power efficiency 25.3 lm/W. The observed PL quantum efficiency (0.43) of the [Ir(msippy)3] in CH2Cl2 shows slightly higher than that of reported Ir(ppy)3 (Φ = 0.40).

Synthesis and Characterization of Poly(fluorenylenevinylene-terphenylenevinylene) Containing Phenyl Pendant Group

Poly(fluorenylenevinylene-terphenylenevinylene) containing phenyl pendant group was synthesized by Suzuki coupling reaction and characterized by1H-NMR,13C-NMR, and IR-spectrum. The weight average molecular weight (Mw) of the obtained polymer was 31,000 with a polydispersity index of 1.9. The polymer showed good solubility in common organic solvents, and the solution and film emitted blue emission (λmax=460 nm) on irradiation with UV light. The ITO/PEDOT/polymer/Al device fabricated using the polymer as an emitting layer emitted blue light with a maximum peak around 460 nm. The maximum efficiency of the device was 0.011%.

Synthesis and Characteristics of New Poly(p-phenylenevinylene) with Bulky t-Octylphenoxy Group

A new 2,5-di(t-octylphenoxy) group substituted poly(p-phenylenevinylene) derivative was synthesized by Gilch polymerization. The obtained polymer was characterized by NMR, FT-IR, and chemical analysis and completely soluble in common organic solvents. The polymer showed good thermal stability withTgof 105 °C. The polymer dissolved in chloroform showed maximum emission at 514 nm with a shoulder peak at around 560 nm. The EL spectrum of the ITO/PEDOT/TOP-PPV/Al device was observed maximum emission at 545 nm with a shoulder peak at around 585 nm.

TOWARD EFFICIENT ELECTRON-TRANSPORTING AND BLUE-EMITTING MATERIALS FOR ORGANIC LIGHT-EMITTING DIODES: STRUCTURE AND PHOTOLUMINESCENT PROPERTIES OF SILOLE DERIVATIVES

The potential blue-emitting as well as electron-transporting materials, 2,5-bis(3,5-trifluoromethylphenyl)-1,1-dimethyl-3,4-diphenylsilole (silole = silacyclopentadiene) (1) and 2,5-bis(3,5-trifluoromethylphenyl)-1,1-diphenyl-3,4-diphenylsilole (2), were synthesized by the Pd-mediated cross coupling reaction of corresponding bis(pheny-lethynyl)silanes with 1-bromo-3,5-trifluoromethylbenzene via intramolecular reductive cyclization. The structure of 2 was established by single-crystal X-ray diffraction analysis. In crystal structure, the dihedral angle between the functionalized phenyl groups containing CF3 at 2,5-position and central silole ring is about 48.70(6)°, showing the diminution of effective conjugation. These compounds exhibited high thermal stability without degradation up to 200°C. The absorption and photoluminescent properties, and cyclic voltametry have been evaluated. Compounds 1 and 2 in thin films showed intense blue emissions at 464–473 nm, respectively, in photoluminescence (PL). In electrochemistry, the reduction potential of 1 and 2 were at -1.92 and -1.81 V, respectively. The presence of substituents at 2,5′ — and/or 1,1′ — positions of siloe ring affected the LUMO energy levels through σ*–π* conjugation.

Synthesis and Characteristics of Novel Poly (Terphenylenevinylene) Derivative Containing Benzoxazolyl Group

Poly(1,4-phenylene-2′-methoxy-5′-ethylhexyl-1′,4′-phenylene-1″,4″-phenylene- α -benzoxazolylvinylene) (PTPBOV) was synthesized through the Suzuki reaction of diboronic acid and dibromide and following end-capping reaction. The electron affinity level of the PTPBOV containing benzoxazolyl group was 2.76 eV.