Isao Yamaguchi

Bluish-violet light-emitting liquid crystalline hyperbranched polymers using three trisalcohol B3 monomers: Preparation, characterisation and structure–property relationship

Bluish-violet light-emitting liquid crystalline (LC) A2+B3 type hyperbranched (HB) polymers composed of an internal 2,5-diphenyl-1,3,4-thiadiazole (DTD) as a mesogen were prepared by melt polycondensation of a dimethyl ester A2 monomer with three trisalcohol B3 monomers, and the effect of the B3 monomer structures on LC and optical properties in the A2+B3 type HB polymers was evaluated. All the HB polymers 4a and 4b, having short aliphatic spacers between the central site of the B3 monomers and the DTD unit, formed thermotropic smectic phases independent of feed mole ratios of A2/B3, and the phase transition temperatures and LC temperature ranges depended on the molecular weights of their HB polymers. However, in the HB polymers 4c, having long aliphatic spacers and a benzene ring between the central site of B3 monomers and the DTD unit, only the HB polymer 4c1 prepared in the highest feed mole ratio of A2/B3 = 3/1 showed the LC property, probably due to steric hindrance of the B3 monomer 3c. The HB polymers 4a and 4c displayed UV-vis absorption and photoluminescence spectra with bluish-violet light emission on the basis of the DTD unit, at almost the same wavelengths in chloroform solutions independent of the feed mole ratios of A2/B3 and the B3 monomer structures, but the spectra of 4a and 4c in film displayed peak maxima at wavelengths depending on the feed mole ratios of A2/B3 and the B3 monomer structures because of intermolecular interactions or aggregations.

Novel liquid crystalline hyperbranched polyesters with interior 4,7-diphenyl-2,1,3-benzothiadiazole units

Novel hyperbranched (HB) polyesters with interior 4,7-diphenyl-2,1,3-benzothiadiazole (DBT) units were prepared by melt polycondensation of a dimethyl ester derivative of DBT (BMBT) (A2 monomer) with 2-hydroxymethyl-2-methyl-1,3-propanediol (HMP) (B3 monomer) at various mole ratios (A2/B3) via an A2 + B3 approach. The liquid crystalline (LC) and optical properties were investigated. FT-IR and 1H NMR spectroscopies revealed that the HB polymers have good solubility in chloroform, and can be synthesized without gelation during the polymerization with a degree of branching (DB) of 36–94%. The branched structures of HB polymers are dependent on the feed mole ratio. The HB polymer prepared from a mole ratio of A2/B3 = 1/3 had the highest number average molecular weight (Mn) and a more linear structure than the other HB polymers (A2/B3 = 3/1, 2/1, 3/1 and 1/2), which had the lowest DB values. DSC measurements, polarizing microscopy observations and X-ray analyses suggested that the HB polymer (A2/B3 = 1/3) forms the smectic A phase, whereas the others formed the smectic C phase. UV-vis and photoluminescent (PL) spectra in the solutions and in films indicated that the HB polymers show maximum absorbances and yellow-light emission attributable to the DBT unit. The PL spectra of HB polymers in film showed another broad peak, which was likely to be due to interchain interactions or aggregations, at longer wavelengths. Relative quantum yields (Φ) of the HB polymers in the chloroform solutions were lower than those of HB polymers comprising the 2-phenylbenzothiazole unit. Polarized absorption and fluorescent spectra revealed that the HB polymers have poor orientation properties and the luminescent properties are independent of the orientation structures of HB polymers.

Synthesis and optical and electrical properties of self-doped copolymers consisting of N-4-sulfopropylaniline and 3,4-ethylenedioxythiophene units

Polymerization of aniline with 3,4-ethylenedioxythiophene (EDOT) in several molar ratios using ammonium persulfate yielded copolymers consisting of p-aminophenylene (unit A) and 3,4-ethylenedioxythiophene-2,5-diyl (unit B). The content of units A and B in the copolymers depended on the monomer feed ratio. Treatment of the copolymers with sodium hydride deprotonated the NH groups to give polyanions. Subsequent treatment of these polyanions with 1,3-propanesultone yielded copolymers with sodium N-propylsulfonate side groups, which were converted into N-propylsulfonic acid moieties by treatment with diluted hydrochloric acid. The copolymers exhibited absorption peaks at approximately 330 and 650 nm, which can be ascribed, respectively, to the benzenoid π–π* and quinoid n–π* transitions of unit A. The copolymers were subjected to electrochemical oxidation, which was dependent on the contents of units A and B. The electrical conductivity of copolymers with N-propylsulfonic acid side chains was found to be higher than that of copolymers bearing sodium N-propylsulfonate groups.

Synthesis and chemical properties of polyphenols with oligoaniline pendant groups

Horseradish peroxidaze (HRP)- or N,N′-bis(salicylidene)ethylenediamineiron(III)-catalyzed polymerizations of 4-(4-phenylaminophenylamino)phenol (monomer-1) and 4-[4-(4-phenylaminophenylamino)phenylamino]phenol (monomer-2) caused oxidative coupling at the hydroxyphenyl group to yield polyphenols (PPs) with pendant oligoaniline (OAN) groups. UV-vis measurements suggested that the OAN pendant groups of the polymers were oxidized in air, resulting in the formation of quinoid structures, which were converted into benzonoid structures by treatment with hydrazine monohydrate. The polymers were electrochemically oxidized in solution.

Eco-friendly synthesis of ionic helical polymers and their chemical properties and reactivity

Reaction of N-(2,4-dinitrophenyl)pyridinium chloride (salt(Cl−)) with sodium dicyanamide (Na(CN)2N) resulted in anion exchange between Cl− and (CN)2N− to yield a new Zincke salt, salt((CN)2N−). Reactions of salt((CN)2N−) with piperazine, specifically (R)-(−)- or (S)-(+)-2-methylpiperazine under eco-friendly conditions, such as in aqueous solution, in the absence of a catalyst, and at room temperature, resulted in pyridinium ring opening to yield ionic high-molecular-weight polymers with 5-2,4-dienylideneammonium dicyanamide units or chiral 5-(2-methylpiperazinium)-2,4-dienylideneammonium dicyanamide units, namely, polymer(H;(CN)2N−), polymer(R-Me;(CN)2N−), and polymer(S-Me;(CN)2N−). UV-Vis measurements revealed that the π-conjugation system expanded along the polymer chain due to the orbital interaction between the electrons on the two nitrogen atoms of the piperazinium ring. Circular dichroism (CD) measurements revealed a helical conformation of the main chain in polymer(R-Me;(CN)2N−) and polymer(S-Me;(CN)2N−). The reaction of polymer(H;(CN)2N−) with p-phenylenediamine (PDA) caused recyclization of the 2,4-dienylideneammonium unit and resulted in depolymerization to yield N-(4-aminophenyl)pyridinium dicyanamide. Cyclic voltammetry analysis suggested that the polymers obtained in this study undergo electrochemical oxidation and reduction.

Chemical properties and self-assembled-ordered structures of π -conjugated cooligomers consisted of 2,6-dialkoxynaphthalene-1,5-diyl, 2,1,3-benzothiadiazole-4,7-diyl, and 1,4-phenylenediethynylene units

Abstractπ-Conjugated cooligomers consisted of 2,6-dialkoxynaphthalene-1,5-diyl (RNap), 2,1,3-benzothiadiazole-4,7-diyl, and 1,4-phenylenediethynylene units were synthesized by Pd-complex-catalyzed condensation reactions. The UV–Vis, photoluminescence, and powder X-ray diffraction measurements suggested that the oligomers have self-assembling-ordered structures in the solid state. The ordered structures depended on the distance between the RNap units of the oligomers. The oligomers underwent electrochemical oxidation (p-doping), which occurred at lower potentials for films than for acetonitrile solutions containing [Et4N]BF4. This effect is caused by the longer π-conjugation lengths of the oligomers in films, which was attributed to molecular self-assembly leading to ordered structures in the solid state.

Self-doped N-4-sulfopropylaniline–3, 4-ethylenedioxythiophene copolymers Synthesis and optical and electrical properties

Polymerization of N-4-sulfopropylaniline with 3,4-ethylenedioxythiophene (EDOT) in several molar ratios using ammonium persulfate yielded copolymers (PPrSO3H) consisting of N-4-sulfopropylaminophenylene (unit A) and 3,4-ethylenedioxythiophene-2,5-diyl (unit B). The corresponding copolymers (PBu) consisting of N-butylaminophenylene (unit C) and unit B were synthesized by the reaction of N-butylaniline and EDOT. The content of units A, B, and C in the copolymers depended on the monomer feed ratio. The ultraviolet–visible spectrum of PPrSO3H exhibited absorption peaks at approximately 420 nm and above 850 nm assignable, respectively, to polaron and bipolaron bands. The copolymers were subjected to electrochemical oxidation, which was dependent on the contents of units A and C. The electrical conductivity of PPrSO3H was found to be higher than that of PBu.

Synthesis and chemical properties of polyphenylenes cross-linked by electron-accepting viologen moiety

Polyphenylene (PP) with NH2 side groups, namely, polymer-1, was synthesized by the Pd-complex-catalyzed reaction of 2,5-dibromoaniline with 9,9-dihexylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester. The reaction of polymer-1 with 1,1′-bis(2,4-dinitrophenyl)-4,4′-bipyridinium dichloride (salt-1) in 1:0.5, 1:1, and 1:2 molar ratios eliminated 2,4-dinitroaniline to yield PPs cross-linked by a viologen (1,1′-disubstituted 4,4′-bipyridinium dications) moiety, polymer-2a, polymer-2b, and polymer-2c, respectively. The UV–vis spectrum of polymer-2c showed absorptions due to the viologen radical cation formed by electron transfer from the polymer backbone to the viologen moiety. The p-doping state of polymer-2c was stable in air. The ESR spectrum of polymer-2c confirmed the generation of the viologen radical. In contrast to photoluminescent polymer-1, the polymers cross-linked by a viologen moiety showed no photoluminescence because the viologen contained within them acted as a quencher. The electrical conductivity of the pellet molded from polymer-2c was higher than that of polymer-1 due to the self-doping in polymer-2c.

Uncatalyzed synthesis of polyphenylacetylene cross-linked by viologen groups and their chemical properties

Polyphenylacetylenes cross-linked with viologen groups (polymers 1a and 1b) were obtained from the reaction of 4-ethynylaniline with 1,1′-bis(2,4-dinitrophenyl)-4,4′-bipyridinium dichloride (salt 1) and the reaction of 4-(1-trimethylsilylethynyl)aniline with salt 1, followed by the deprotection of the trimethylsilyl group. Model compound (model 1) was synthesized by the reaction of 4-ethynylaniline with 1-(2,4-dinitrophenyl)-4,4′-bipyridinium chloride (salt 2). Ultraviolet–visible spectra revealed that the polymers 1a and 1b had an expanded π-conjugation system along the polymer chain: the polymer showed an onset position of absorption at a wavelength approximately 100 nm longer than the corresponding wavelengths of the model compound. Polymers 1a and 1b received a two-step electrochemical reduction in the viologen group within the polymer and an electrochemical oxidation of the polymer backbone.