Nam Choul Yang

Electron injection enhancement by diamond-like carbon film in organic electroluminescence devices

Abstract Diamond-like carbon (DLC) is deposited as an electron injection layer between the organic layer and Al cathode electrode in organic electroluminescence devices (OLEDs) by the use of Cs+ ion gun sputter deposition system. The devices consist of; indium tin oxide/PEDOT:PSS/MEH-PPV/DLC/aluminum. Electron injection properties have been investigated by I–V characteristics at various deposition conditions and the mechanism of electron injection enhancement due to a thin DLC layer has been studied. The characteristics of DLC film deposited at various negative carbon ion energies are examined by Raman spectroscopy. Optical microscope is also used to observe the Al surface after the light emission test. It is found that the sp2/sp3 ratio and electron affinity of DLC film are varied as the carbon ion energy increases from 50 to 200 eV, which enhance the electron injection and improve the property of OLEDs. An order magnitude increase in current is obtained from DLC layer inserted devices and the device stability is also improved.

Synthesis and optically acid-sensory properties of novel polyoxadiazole derivatives

Abstract New organo-soluble and blue-emissive fluorene-based polyoxadiazoles, PFO x and PFO x EH, exhibit colorimetric and fluorescent acid-sensory properties to a strong acid due to the weak basicity of imine-type nitrogen atom(s) in an 1,3,4-oxadiazole ring. To further investigate their protonation with an acid, 1 H NMR spectroscopy and AM1 semiempirical quantum-mechanics are utilized as well as UV–visible absorption and fluorescence spectroscopies. These investigations indicate the protonation does not proceed thermodynamically but kinetically at the initial stage of the complex formation of an acid and an oxadiazole ring in the polymer backbone.

Introduction of Diphenylmaleimide Moieties into the Main Chain of Fully π-Conjugated Poly(arylene ethynylene)s as ‘Kink’ Structures

Novel fully π-conjugated poly(arylene ethynylene)s 1 and 2 having diphenylmaleimides in the backbone were prepared utilizing a Pd(0)-Cu(I) catalyzed coupling reaction (Sonogashira method) of N-alkyl substituted 1,2-di(4-bromophenyl) maleimides (5 and 6) with 1,4-diethynylbenzene. Whereas polymer 1 with an N-hexyl side chain showed low solubility, 2 having an N-dodecyl group was completely soluble in common organic solvents. Determined by GPC, M w of 2 was 45 800 Da with a polydispersity index of 2.5. Polymer 2 showed UV-visible absorption maxima at 330 nm and 413 nm and greenish yellow fluorescence with a maximum of 530 nm.

The fluorescent effects on theN-substituents of polyarylenevinylenes having 1,2-diphenylmaleimide moieties

Model compounds and polymers havingN-substituted 1,2-diphenylmaleimide moieties were synthesized and characterized by NMR, IR, UV, and fluorescence spectroscopy. The fluorescence intensity could be controlled byN-substituents of model compounds and polymers. As the structure of anN-substituent of them was bulkier, or the electron density of anN-substituent was denser, the photoluminescence intensity was increased. All the compounds showed greenish yellow photoluminescence with the maximum intensity between 510 and 537 nm. From quantum efficiency data of the model compounds and the polymers, the fluorescence intensity of the polymer11 was higher than that of the model compound4.

The synthesis and redox-induced off-on PL properties of poly(3,4-bisphenyl-N-methylferrocene-pyrrole-2,5-dione)

Abstract A novel π-conjugated polymer containing a ferrocene group was designed and synthesized from 3,4-bis(4-bromophenyl)- N -methylferrocene-pyrrole-2,5-dione by dehalogenation polycondensation with the zerovalent nickel complexes (a Yamamoto reaction). The polymer was characterized by FT-IR, 1 H NMR, gel permeation chromatography, UV, cyclic voltammetry and Fluorescence spectroscopy. The polymer has the M w of 2620 and polydispersity index of 1.5. Also this polymer showed high solubility in common organic solvents, good film formability on the glass substrate and redox property. The fluorescence of the model compound and polymer with a diphenylmaleimide moiety is almost quenched due to the ferrocene group because of the intramolecular electron transfer. However, the model compound and the polymer showed a recovered fluorescence when a ferrocene group of them was oxidized chemically and electrochemically.