Naoki Noma

Organic light-emitting diodes using a novel family of amorphous molecular materials containing an oligothiophene moiety as colour-tunable emitting materials

A novel family of amorphous molecular materials containing an oligothiophene moiety with varying conjugation length function as thermally and morphologically stable, colour-tunable emitting materials for organic light-emitting diodes (LEDs). Tuning of the emission colour from light blue to orange is achieved by varying the conjugation length of the oligothiophene moiety. Double-layer organic LEDs that use this novel class of amorphous molecular materials as an emitting layer and tris(quinolin-8-olato)aluminium or 1,3,5-tris[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene as an electron-transport layer exhibit high performances.

Photoelectrical conversion of p-n heterojunction devices using thin films of titanyl phthalocyanine and a perylene pigment

Two types of p-n heterojunction devices consisting of thin films of titanyl phthalocyanine (TiOPc) and N,N′-dimethyl-3,4:9,10-peryle-nebis(dicarboximide) (MPCI), sandwiched between indium tin oxide (ITO) and gold (Au), have been fabricated, and their performance characteristics investigated. The devices showed a response to light over the whole visible wavelength region from 400 to 900 nm. The cell with a structure of ITOMPCITiOPcAu (Type A) was superior to the cell with a structure of ITOTiOPcMPCIAu (Type B) in the conversion efficiency. The cell of type A exhibited conversion efficiencies of ca. 0.7% for the monochromatic light of 470 or 720 nm reaching the organic layer through the electrode, and ca. 0.35% for incident white light (8–130 mW cm−2).

A novel yellow-emitting material, 5,5′′-bis{4-[bis(4-methylphenyl)amino] phenyl}-2,2′:5′,2′′-terthiophene, for organic electroluminescent devices

A novel amorphous molecular material, 5,5′′-bis{4-[bis(4-methylphenyl)amino]phenyl}2,2′:5′,2′′-terthiophene (BMA-3T), has been found to function as a yellow-emitting material in organic electroluminescent (EL) devices. Both the single layer EL device using BMA-3T alone and the double layer EL device consisting of an emitting layer of BMA-3T and an electron-transport layer of tris(8-quinolinolato)aluminum sandwiched between indium-tin-oxide (ITO) and an alloy of magnesium and silver (∼10:1) electrodes emitted a bright yellow light resulting from BMA-3T. The double layer EL device showed much better performances than the single layer EL device, exhibiting a maximum luminance of ∼13 000 cd m−2 at a driving voltage of 18 V, and a luminous efficiency of 1.1 lm W−1 at a luminance of 300 cd m−2.

Polymers containing pendant oligothiophenes as a novel class of electrochromic materials

Vinyl polymers containing oligothiophenes, e.g. 2,2′ : 5′,2″-terthiophene and 2,2′ : 5′,2″ : 5″,2‴-quaterthiophene, as pendant groups have been found to constitute a novel class of potential electrochromic materials. The electrochemically doped polymers undergo reversible, clear colour changes from bluish purple to pale yellowish orange, and from green to pale yellow, respectively, and vice versa on electrochemical dedoping and doping.

Electrochemical doping of poly[4-(N,N-diphenylamino)phenylmethyl methacrylate], and rectification and photovoltaic properties

Abstract An insulating, photoconductive polymer, poly[4-(N,N-diphenylamino)-phenylmethyl methacrylate] (PDAPM), has been transformed into a semiconductive polymer by electrochemical doping. The electrochemically-doped PDAPM is a partially oxidized cation radical salt with ClO4− as a dopant, and its structure is partially cross-linked at the paraposition of the phenyl group in the triphenylamine moiety owing to the coupling reaction of the cation radical. The electrochemically-doped PDAPM film sandwiched between aluminum and gold electrodes shows rectification and photovoltaic effects.

Electrochemically doped poly(N-Vinylcarbazole) as an electrode material for rechargeable batteries

Abstract Secondary lithium batteries using electrochemically-doped poly(N-vinyl-carbazole) (PVCz) deposited on a Pt plate or gauze, and doped PVCz-graphite as cathodes exhibit flat discharge voltages and good cyclability with high coulombic efficiencies.

Structure and electrical conductivity of a solid salt obtained by electrochemical oxidation of a thiophene dodecamer

Abstract A new thiophene dodecamer having four octyl groups at the β-position of the thiophene ring, 4Oc12T, was synthesized and its electrochemical doping and the electrical properties of the resulting electrochemically-oxidized salt were investigated. Electrochemical doping of a film of 4Oc12T by anodic oxidation produced a dark blue-colored salt. It was identified as a twoelectron oxidized salt from the electronic absorption, infrared absorption, and electron spin resonance spectra and elemental analysis. The electrochemically-oxidized 4Oc12T was found to exhibit a high room-temperature conductivity of ca. 10 S cm −1 with an activation energy of 0.05 eV.

Materials chemistry communications. Electrochemical doping of α-ethyl-disubstituted oligothiophenes and electrical conductivities of the resulting radical-cation salts

Electrochemical doping of α-ethyl-disubstituted oligothiophenes and the electrical conductivity of the resulting radical-cation salts have been studied. 5,5‴-Diethyl-2,2′:5′,2″:5″,2‴-quaterthiophene (DEt4T) and 5,5â�—-diethyl-2,2′:5′,2″:5″,2‴:5‴,2â�—-quinquethiophene (DEt5T) are found to contrast with each other in the stoichiometry and electrical properties of the resulting solid radical-cation salts. The DEt4T and DEt5T radical-cation salts with a doping extent of ca. 100 and 50%, respectively, produced by electrochemical doping exhibited room-temperature conductivities of 9 × 10–8 and 5 × 10–3 S cm–1 with activation energies of 0.54 and 0.11 eV, respectively.

Synthesis and electrical properties of novel electrochemically-doped vinyl polymers containing ‘end-capped’ quaterthiophene and quinquethiophene as pendant groups

Abstract For the purpose of developing a novel class of electrically conducting polymers, electrochemically-doped vinyl polymers containing ‘end-capped’ quaterthiophene and quinquethiophene as pendant groups have been prepared by electrolytic polymerizations of the corresponding vinyl monomers in dichrolomethane containing tetrabutylammonium perchlorate. The electrochemically-doped polymers were identified as partially oxidized radical-cation salts with ClO 4 − as a dopant, as evidenced from the electronic and infrared absorption spectra and elemental analysis. The eletrochemically-doped polymers containing ‘end-capped’ quaterthiophene (degree of doping: 49%) and quinquethiophene (degree of doping: 66%) as pendant groups exhibited room-temperature conductivities of 3 × 10 −8 and 2 × 10 −5 S cm −1 with activation energies of 0.49 and 0.32 eV, respectively.

Preparation of electrically conducting polymers containing pendant π-electron systems by electrochemical doping, and properties and applications of doped polymers

Abstract In order to develop a new type of electrically conducting material, studies of electrochemical doping of vinyl-type polymers containing pendant π-electron systems have been made, and the properties and applications of the doped polymers investigated. Electrical properties of the doped polymers are discussed in relation to structures. Performance characteristics of rechargeable batteries using electrochemically-doped polymers as cathode materials, and rectification and photoelectrical properties of the doped polymers are discussed.