Takaki Kanbara

Direct arylation polycondensation for the synthesis of bithiophene-based alternating copolymers

Direct arylation polycondensation reactions using a simple catalytic system gave eight kinds of bithiophene-based alternating copolymers. The conditions for the reactions of 3,3′,4,4′-tetramethylbithiophene with dibromoarylenes were optimized to obtain high-molecular-weight polymers without formation of cross-linked structures. In the reaction of a dibromoarylene containing a reactive C–H bond, a short reaction time (1.5 h) was suitable for preventing side reactions. In contrast, a long reaction time (6 h) gave high-molecular-weight polymers from dibromoarylene monomers without a reactive C–H bond. This polycondensation reaction enables the synthesis of polymers containing dye structures such as diketopyrrolopyrrole and isoindigo, which are applicable as materials for polymer solar cells.

Preparation of new type of azacalixarene, azacalix[n](2,6)pyridine

Abstract Palladium-catalyzed aryl amination of 2,6-dibromopyridine with 2,6-bis(methylamino)pyridine or 2-bromo-6-(methylamino)pyridine gave new azacalix[ n ](2,6)pyridines ( n =4 and 6). Molecular structure, conformation, and complexation of the macrocycles toward zinc ion were characterized by NMR spectroscopy and X-ray crystallography.

Detailed Optimization of Polycondensation Reaction via Direct C–H Arylation of Ethylenedioxythiophene

The polycondensation reaction of 3,4-ethylenedioxythiophene with 2,7-dibromo-9,9-dioctylfluorene via Pd-catalyzed direct arylation gives poly[(3,4-ethylenedioxythiophene-2,5-diyl)-(9,9-dioctylfluorene-2,7-diyl)]. The reaction conditions are optimized in terms of the Pd precatalysts, reaction time, and carboxylic acid additives. The combination of 1 mol% Pd(OAc)(2) and 1-adamantanecarboxylic acid as an additive is the optimized catalytic system, and it yields the corresponding polymer with a molecular weight of 39,400 in 89% yield. The polycondensation reaction, followed by an end-capping reaction, effectively provides a linear polymer without Br terminals.

POLYQUINOXALINE AS AN EXCELLENT ELECTRON INJECTING MATERIAL FOR ELECTROLUMINESCENT DEVICE

Electron injecting properties have been studied for one of polyquinoxaline (PQx) derivatives. PQx was clarified to be an excellent electron injecting material for electroluminescent (EL) device because it has many advantageous properties such as high electron affinity, good thermal stability, good processability, and sufficiently low refractive index. On the other hand, since poly(p‐phenylenevinylene) (PPV) was known as a good hole injecting material, an EL device with ITO/PPV/PQx/metal type structure was suggested. It was shown that the quantum efficiency of the cell was higher than that of ITO/PPV/metal cell. Related physical and optical properties of PQx derivatives are also investigated.

Preparation of a new receptor for anions, macrocyclic polythiolactam—structure and high anion-binding ability

Thiocarbonylation of a macrocyclic tetralactam gave a new macrocyclic tetrathiolactam. The chemical transformation enhances hydrogen-bonding ability of the NH protons in the cavity of the macrocycle, and provides strong affinity toward anions. The association properties of the polythiolactam with anions was examined, and molecular structures of the macrocycle and its Cl− complex were determined.

Synthesis of 4,4′-dinonyl-2,2′-bithiazole-based copolymers via Pd-catalyzed direct C–H arylation

Direct arylation polycondensation of a bithiazole derivative with dibromoarylenes gave the corresponding bithiazole-based copolymers using the phosphine-free catalytic system in a short reaction time.

A sensitive and selective method for determination of gold(III) based on electrothermal atomic absorption spectrometry in combination with dispersive liquid-liquid microextraction using dicyclohexylamine.

A combined method with dispersive liquid-liquid microextraction (DLLME) and electrothermal atomic absorption spectrometry (ETAAS) has been developed for determining gold(III). Dicyclohexylamine, a new extractant for gold(III), showed excellent performance in DLLME. Acetone was indispensable to the quantitative extraction of gold(III), contributing to decrease in hydration, decrease in the difference in the dielectric constants between the supernatant phase and the sedimented phase, and dissolution of a part of chloroform as an extraction solvent to the supernatant phase as well as improvement of dipersibility. In DLLME using a mixture of 1.0mL of acetone and 100microL of chloroform containing 50mmolL(-1) of dicyclohexylamine, gold(III) could be extracted selectively and effectively from 8mL of a sample solution in the presence of iron(III), cobalt(II), nickel(II), copper(II), palladium(II), and platinum(IV) at pH 1. The extracted gold(III) was determinable by ETAAS; the detection limit was 0.002microgL(-1) (three times the standard deviation of the blank values, n=8) as a gold(III) concentration in 8mL of sample solution. The proposed method was applicable to the determination of gold in platinum metal and its alloy as well as effluent without any interference by the matrices.

The effect of a solvent on direct arylation polycondensation of substituted thiophenes

In the direct arylation polycondensation of thiophene derivatives, toluene was found to be a suitable solvent for electron-deficient thiophenes, whereas dimethylacetamide (DMAc) was suitable for electron-rich thiophenes.

Spherical Assemblies from π-Conjugated Alternating Copolymers: Toward Optoelectronic Colloidal Crystals

Self-assembly of conducting polymers, which are often used as photoabsorbing, charge-transporting, and photoemission layers of organic photovoltaic and light-emitting devices, were comprehensively studied by means of slow precipitation from polymer solutions upon addition of a vapor of nonsolvents. Polymers such as polyfluorene and polythiophene having a single monomer component hardly formed defined and discrete objects but only gave ill-defined aggregates. In contrast, alternating copolymers typically having both fluorene and thiophene components in their repeating unit self-assembled into well-shaped spheres with diameters ranging from several hundreds of nanometers to several micrometers. Such clear differences in terms of the assembling geometries derive from the rigidity and crystallinity of the polymers, where the copolymers possess large steric hindrance on their backbone that reduces planarity of the polymers and inhibits anisotropic crystal growth, leading to the formation of structurally isotropic spheres. Changing the assembling parameters can systematically control diameter and deviation of the spheres. Furthermore, photocarrier lifetimes of the spheres were markedly enhanced by more than 3 orders of magnitude in comparison with those of cast films from their solutions. This research gives a useful guide for preparation of colloidal crystals from π-conjugated polymers toward their optoelectronic applications.

Polyquinoxaline as an electron injecting material for electroluminescent device

Abstract A series of 2,3-disubstituted poly(quinoxaline-5,8-diyl) (PQx) was clarified to be an excellent electron injecting material for electroluminescent (EL) devices, since these have many advantageous properties such as high electron affinity (Ea:3.3 ~ 3.4 eV), good thermal stability, good processability and sufficiently low refractive index. On the other hand, since poly( p -phenylenevinylene) (PPV) was known as a good hole injecting material (ionization potential, Ip :5.1eV), an EL device with ITO/PPV/PQx/Metal type structure was suggested. It was shown that the quantum efficiency of the cell was about twice as high as that of ITO/PPV/Metal cell. Related physical and optical properties of PQx derivatives are also investigated.