Nobuo Takamiya

Molecular distribution of photoluminescent Ru(bpy)32+ dispersed in a polymer film and its distance-dependent concentration quenching

Abstract Photoluminescent tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy) 3 2+ ) was dispersed in a polysiloxane film by mixture casting from an ethanol solution. The distance distribution of the dispersed molecules and the distance-dependent concentrations quenching of the photoluminescence were studied. The quenching obeyed a static quenching obeyed a static quenching model, and the quenching distance was obtained by changing the concentration of the complex. A more correct quenching radius of 1.1 nm was obtained by considering the excluded volume of the probe. The distance between the dispersed molecules was discussed in terms of charge hopping between the molecules.

Charge 3ransfer from donor to photoexcited Ru(bpy)32+ in solution and polymer matrix

Electron transfer quenching of photoexcited Ru(bpy) 3 2+ (bpy, bipyridine) by three kinds of hole transport material, phenothiazine (PTZ) and 10-methylphenothiazine (MPTZ) was studied in acetonitrile solution and a polymer film. The quenching rate constants (k q ) with respect to ΔG in acetonitrile solution are discussed in terms of Marcus theory. In poly(ethyleneoxide) (PEO) films, quenching of photoexcited Ru(bpy) 3 2+ was observed and analysed by a static quenching model. The electron transfer distance in the polymer film was found to be 1.1-1.9 nm using a modified Perrin equation considering the excluded volume effect. The dependence of the electron transfer rate on ΔG in the PEO film was larger than that in acetonitrile solution.

Photoresponsive electrode based on the reaction between oxygen and the excited Ru(bpy)2+3 complex incorporated in a coated Nafion film

Abstract A photoresponsive electrode was prepared by coating a Nafion film on a indium tin oxide (ITO) electrode incorporating the Ru(bpy) 2+ 3 complex in the film. A photocurrent was induced at the coated electrode dipped in an aqueous electrolyte in the presence of oxygen. The action spectrum showed that the photocurrent is based on the reaction between O 2 and the excited Ru complex. Viologen molecules present as a solute or as the second film on the top of the Nafion[Ru(bpy) 2+ 3 ] film increase the induced photocurrent by about a factor of two by working as a mediator between the excited Ru(bpy) 2+ 3 and O 2 .

Oxygenation of 3-methylindole catalyzed by cobalt(II) phthalocyanine attached to polyorganosiloxane Part 2. Mechanism for addition of oxygen to 3-methylindole

Oxygenation of 3-methylindole was catalyzed by cobalt(II)phthalocyanine (Co(II)Pc) attached to polyorganosiloxane. The mechanism for the addition of oxygen to 3-methylindole was examined by means of the reaction rate determined from the amount of oxygen consumption. The reaction rate (V) was given as follows: V = K[3-methylindole] [Co(II)Pc][O2]. 3-Methylindole was concluded to be not only a substrate but also an oxidation inhibitor. The oxygenation was considered to proceed via a radical mechanism.

Concentration quenching of photoluminescence of polysiloxane-pendant Ru(bpy) 3 2+ film and intermolecular distance distribution of the complex

Photoluminescent Ru(bpy)32+ complex was covalently anchored on a polysiloxane chain, and photoluminescence of the film was studied. The emission yield becomes lower with higher probe concentration indicating concentration quenching. The intermolecular distance distribution of the probe was obtained by statistical analysis, and the distance for static concentration quenching was 0.83 nm.

Esterolyses of p-nitrophenyl esters catalyzed by dialkylaminopyridines attached to polyorganosiloxane

SummaryThe present study describes the preparation of polyorganosiloxanes containing dialkylaminopyridines in their side chains (POS-DAAPs) and the use of them as catalysts for esterolyses of p-nitrophenyl esters of CH3(CH2)nCOOH (n=0–5). The POS-DAAPs (4, 5) were prepared from poly[(3-chlorocarbonylpropyl)methylsiloxane] (PCCPMS, 1) and two pyridine derivatives, such as 4-[(2-hydroxyethyl)methylamino]pyridine (HEMAP, 2) and 4-[4-(2-hydroxyethyl)piperidino]pyridine (HEPP, 3). Pyridyl groups of POS-DAAPs 4 and 5 were partially quaternized with dimethylsulfate (6, 7) in order to carry out esterolysis in homogenious systems. The esterolyses were examined in methanol/tris(hydroxymethyl)-aminomethane-hydrochloric acid buffer solution (vol. ratio 2/1, pH of buffer solution: 7.5) and analyzed following Michaelis-Menten like kinetics. The second-order rate constants (k2/Km) of the esterolyses catalyzed by POSs 6 and 7 were 22–38 fold values of those catalyzed by the corresponding monomolecular catalysts 2 and 3. In addition, the effects of POSs were discussed from the kinetic, thermodynamic, and activation parameters.

Oxidation of 3-methylindole catalyzed by cobalt(II)phthalocyanines covalently bound to polyorganosiloxane

Two kinds of cobalt(II)phthalocyanines covalently bound to polyorganosiloxane (POS) were prepared to be applied as catalysts for the oxidation of 3-methylindole in organic solvents. The catalytic activity of the POS whose carboxyl residues were methyl-esterified was high compared with that of the POS which has carboxyl residues. The former polymeric atalyst exhibited higher catalytic activity than monomolecular phthalocyanine, indicating an appearance of effects of polymer chains. The factors which influence the catalytic oxidation, e.g., polymer conformations, basicity of solvents, and equilibrium involving phthalocyanine monomer and the dimer, are discussed. It has become apparent that polymer conformation influences catalytic activity and that the catalytic activity of the POS, whose main chains are mobile, is high.

Liquid crystalline side-chain polysiloxanes containing mesogenic groups attached by esterification

SummaryLiquid crystalline side-chain polysiloxanes were prepared without metal complex catalyst. Mesogenic groups such as cholesteryl, 4-cyano-4′-biphenyl and 4-methoxy-4′-biphenyl group were introduced into polysiloxane by esterification and from DSC measurements they were compatible with other liquid crystalline polysiloxanes reported previously.