Rikukawa Masahiro

Novel Langmuir-Blodgett (LB) films were fabricated from mixed monolayers containing stearic acid and various poly(3-alkylthiophene)s, which contained almost 100% head-to-tail couplings. The LB films exhibited well-defined layered structures and self-organized properties of the regioregular polymers. The molecular organization, the layered structures and the electrical properties depended on the regioregularity and the length of the alkyl side chains of the regioregular polymers. The regioregular polymers have considerably improved the electrical conductivity and the third-order optical non-linearity. (C) 1998 Elsevier Science S.A. All rights reserved.

Third-order optical nonlinearity of regioregular head-to-tail coupled poly(3-hexylthiophene)(HT-PHT) was measured using degenerate four wave mixing (DFWM), and the dispersion spectrum of \X-(3)\ around the exciton absorption peak was obtained. In addition, the relaxation process of the excitons was measured using the transient grating method. The resultant decay time was less than 2 ps and consisted of two components.

Poly(oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene) (PEEK) and poly(4-phenoxybenzoyl-1,4-phenylene, Poly-X 2000) (PPBP), were sulfonated with sulfuric acid by incorporating sulfonic acid moieties in order to convert these polymers to proton-conducting polymers. The sulfonated polymers containing 65 mol% sulfonic acid showed a high proton-conductivity of 10(-2)-10(-4) S cm(-1) at room temperature. Sulfonated PPBP showed a much higher and more stable proton conductivity than sulfonated PEEK, which is in agreement with the strong water absorption of the former compound.

A [2]catenane consisting of a π-electron-accepting tetracationic cyclophane of cyclobis(4,4′-azopyridinium-p-phenylene) and a π-electron-donating macrocyclic polyether of bis-p-phenylene-34-crown-10 was synthesized via a template-directed synthesis in 68% yield. The [2]catenane exhibited charge transfer bands with λmax = 526 nm in CH3CN. A precursor of the cyclophane, bis[4-(4-pyridylazo)pyridinium], spontaneously formed a charge transfer complex with the macrocyclic polyether. The investigation of the charge transfer complex using UV-visible and 1H NMR spectroscopy revealed that the complex had a pseudo-rotaxane structure with a stability constant (Ka) of 120 dm3 mol-1 at 25°C in CH3CN. The highly efficient catenation of 68% yield was attributable to cooperative self-assembling processes derived from the strongly π-electron deficient 4,4′-azopyridinium and 4-(4-pyridylazo)pyridinium units. These results suggested that there was a new formation mechanism of the catenated structure through preorganization of the charge transfer complex.

Third-order optical nonlinearity of regioregular head-to-tail coupled poly(3-hexylthiophene)(HT-PHT) was measured using degenerate four wave mixing (DFWM), and the dispersion spectrum of |χ(3)| around the exciton absorption peak was obtained. In addition, the relaxation process of the excitons was measured using the transient grating method. The resultant decay time was less than 2 ps and consisted of two components.

Organic photochrome azopyridiniums were systematically prepared by quaternizing azopyridines with either dimethyl sulfate or 1,3-propanesultone. photochemical, electrochemical, and photoelectrochemical studies on the azopyridiniums as methyl sulfate, hexafluorophosphate, and zwitterionic compounds were carried out in aprotic solvents and in aqueous solutions. The azopyridiniums, which have 3-located quaternized nitrogens to the azo group, exhibited photochemical activity of trans reversible arrow cis isomerization. Quaternization of the pyridine moiety decreased the photochemical conversion between the trans and cis forms. The photochromic properties were influenced by an electronic effect of quaternized nitrogens and an electrostatic interaction of counter anions. In electrochemical studies, new redox-active azopyridiniums were found by using cyclic voltammetry and an electrochemical technique coupled with UV-vis spectroscopy. By the quaternization of azopyridines, the formal reduction potentials were shifted to a positive region up to -0.27 V vs. Fc/Fc(+). The reversibility of the electrochemical reactions was strongly dependent on the location of quaternized nitrogen. The trans reversible arrow cia photoisomerization of electroactive azopyridiniums influenced their electrochemical properties. The photochromic molecules exhibited a photoelectric effect, which was a change in the cathodic limiting currents of azopyridiniums, reversibly modulated by ultraviolet light of an external stimulation.

We measured the third-order optical nonlinearity of regioregular head-to-tail coupled poly (3-hexylthiophene) (HT-PHT) and regiorandom poly (3-hexylthiophene) (R-PHT) around exciton resonance using degenerate four wave mixing. The observed value of |χ⁽³⁾| at the exciton resonance peak of HT-PHT is in the order of 10^-9 esu which is approximately three-fold larger than that of R-PHT. We observed for the first time the enhancement in optical nonlinearity that occurs through the control of regularity of the polymeric structure. Response time of the nonlinearity was also measured using the transient grating method. The decay time of the transient grating in R-PHT and HT-PHT was less than 2 ps.

The mixed fullerene/phthalocyaninatometal monolayers were successfully deposited as Y-type films by the vertical lifting method with a transfer ratio of about unity, although the fullerene monolayers were too stiff to transfer homogeneous multilayer films onto solid substrates. The molecular organizations of fullerene and phthalocyaninatometals in the LB films were influenced by center-metal ion species of phthalocyaninatometals. High photocurrent with a short photoresponse time was observed by the irradiation of UV-Vis:is light to these LB films.

New bisaxially coordinated phthalocyaninatoiron complexes were synthesized by melting azopyridines and phthalocyaninatoiron. Monolayers of azopyridineiphthalocyaninatoiron complexes were spread from their benzene solutions, and the x-A isotherms were measured The multilayer thin films were fabricated by the Langmuir-Blodgett technique. The structure of the multilayer thin films was investigated by UV-Vis spectra, X-ray diffraction, and FT-IR measurements. These LB films are rendered electrically conductive by doping with strong oxidizing agents such as NOPF6, I-2, and SbCl5.

Tetracationic cyclophanes and a [2]-catenane consisting of cyclobis(azopyridinium-p-phenylene) were synthesized via the template-directed synthesis. The charge transfer transitions and stability constants for supramolecular complexes with hydroquinone derivatives were evaluated by using visible spectroscopy and spectroscopic titration.

Highly ordered polypeptide Langmuir-Blodgett films Hem fabricated from poly(glutamic acid) derivatives. The poly(glutamic acid) derivatives formed stable monolayers at the air-water interface that could be deposited onto solid substrates. The alpha-helix structure of the poly(glutamic acid) derivatives was confirmed by FT-IR and CD spectrum measurements. Monolayers of tetra-tert-butylphthalocyaninatoiron awe transferred onto the poly(glutamic acid) derivative LB films. butylphthalocyaninatoiron molecules existed in the multilayer thin films due to the molecular template effect of the polypeptide IB film. The electrical and optical properties of the multilayer thin films transferred tetra-tert-butylphthalocyaninatoiron or other metal phthalocyanines onto polypeptide LB films were also investigated.

The conductive ultra thin films were fabricated from mixed monolayers containing stearic acid and Head-to-Tail poly(3-alkylthiophene). These films exhibited well-defined layered structures as determined by optical absorption and X-ray diffraction measurements. The UV-Vis absorption spectra of these films showed lower energy absorption shifts of 48 nm from that of the random poly(3-alkylthiophene)/stearic acid LB films. The blue shift of absorption maximum of the LB film is attributed to the increase of pi-conjugation length caused by no steric hindrance of alkyl side chains. The conductivity of the Head-to-Tail poly(3-hexylthiophene)/stearic acid LB films was greatly improved in the range of 67-100 S/cm.

The preparation and electrical properties of iodine-doped phthalocyaninatoiron polymers {[Fe(Pc)L]I-y}(n) and {[Fe(pc(tb))L]I-y}(n) {Pc=phthalocyaninato, Pc-tb=tetra-tert-butylphthalocyaninato, L=4,4'-azopyridine (4,4'-APy) and octafluoro-4,4'-azopyridine (4,4'-FAPy)} were investigated. The stoichiometry of polymer complexes was determined by TG/DTA. The iodine-doped {[Fe(Pc)(4,4'-APy)]I-y}(n) complexes were semiconducting materials in the range of 10(-4) to 10(-10) S/cm.

Syntheses of phthalocyaninatoiron complexes, Fe(Pc-tb)L-2 and [Fe(Pc-tb)L](2) (where Pc-tb=tetra-tert-butylphthalocyaninato, L = 4,4'-azopyridine (4,4'-APy) or octafluoro-4,4'-azopyridine (4,4'-FAPy)}, were carried out. These complexes were characterized with TG/DTA H-1 NMR, W-visible spectroscopy, and cyclic voltammetry. Voltammetric measurements of soluble Fe(Pc-tb)L-2 in benzene solutions revealed th at co ordination of axi al ligands on Fe(Pc-tb) greatly influenced oxidation potentials og the central metal moiety. The correlation between conductivities of polymeric [Fe(Pc-tb)L](n) complexes and bandgaps determined by the voltammetric measurements was identified.

Conductive Langmuir-Blodgett (LB) films were fabricated from mixed monolayers containing structurally homogeneous poly(3-hexyl-thiophene) and stearic acid in different molar ratios. The structure of these mixed LB films was probed by visible absorption and X-ray diffraction measurements. These regioregular polymers containing almost 100% head-to-tail couplings showed the self-organized properties and affected the molecular structure in the LB films. Conductivities of the LB films doped with strong oxidizing agents were dramatically improved due to their well-defined polymer structure and were in the range of 10(2)-10(1) S cm(-1).

High-performance composites of vinylpyridine-styrene copolymers and polyamic acid (PAA) were prepared by the so-called 'in situ polymerization method'. Poly(4-vinylpyridine-co-styrene) (P4VPy-St) and poly(2-vinylpyridine-co-styrene) (P2VPy-St) were used as flexible matrix polymers. A molecular composite could be obtained from a polymer pair having an attractive interaction such as a coulombic interaction. Their morphologies were observed by scanning electron microscopy (SEM); mechanical properties of these composites were studied by tensile tests. The PAA content dependence of tensile strength for the composite films obtained by the in situ polymerization method was investigated. The tensile strength of the resulting composite was about 1.5 times higher than that of PAA film. The coulombic interaction between the pyridine moiety in the matrix copolymer and resulting PAA enhanced both the miscibility and mechanical properties of the composites. Furthermore, a polyimide (PI) structure was formed by stepwise heat-treatment and greatly enhanced the tensile strength of the composite films.

Conductive ultra thin films were fabricated from mixed monolayers containing stearic acid and structurally homogeneous poly(3-hexylthiophene), which had almost 100% head-to-tail couplings with a M(w) of 8100 (M(w)/M(n) = 1.5) as estimated by H-1 NMR, C-13 NMR, and gel permeation chromatography. The mixed monolayers were found to be stable at the air-water interface and could be readily deposited onto solid substrates as Y-type films by the vertical lifting method. These Langmuir-Blodgett (LB) films exhibited well-defined layered structures as determined by UV-Vis absorption and X-ray diffraction measurements. The conductivity of the mixed LB films doped with NOPF6 was in the range of 50-100 S cm(-1) and was 50- to 100-fold higher than that of the mixed LB films using poly(3-hexylthiophene) synthesized by the usual chemical oxidation with FeCl3.

Poly(L-glutamate)s (PLG) having NLO active chromophore in side chains were synthesized by an ester exchange reaction of methyl ester of PLG with 4-(3-hydroxypropoxy)-4'-nitrostilbene or other alcohols containing the nitrostilbene moiety, and the NLO properties of these polymers were investigated in terms of second harmonic generation (SHG). These polymers exhibited rather stable poled structures after electric poling, possibly owing to the helical structures of PLG. Aromatic polymers such as poly(p-phenylene) are thermally stable with high glass transition temperatures. Poly(p-phenylene) derivatives having various donor or acceptor groups were used to measure NLO properties in terms of SHG and third harmonic generations (THG). They showed high SH coefficients with less relaxation behaviors of the poled structures.

The in-situ polymerization of acrylamide in solutions of poly(styrene) (PSt) was carried out by amionic polymerization to form Nylon 3 in PSt as micro-composites in which Nylon 3 was dispersed as fine particles. Copolymers of styrene (St) and 4-vinylpyridine (4-VPy) were used as matrix polymers in order to improve a compatibility between the in-situ formed Nylon 3 and matrix polymer through hydrogen-bonding. These micro-composites showed great improvement of mechanical properties owing to reinforcement by ultra-fine particles of Nylon 3. Especially, the micro-composite derived from poly(St-co-4-VPy) showed excellent improvements of mechanical properties owing to the hydrogen bonding interactions between Nylon 3 and 4-VPy.

Poly(L-glutamate)s (PLG) having NLO active chromophore in side chains were synthesized by an ester exchange reaction of methyl ester of PLG with 4-(3-hydroxypropoxy)-4'-nitrostilbene or other alcohols containing the nitrostilbene moiety, and the NLO properties of these polymers were investigated in terms of second harmonic generation (SHG). These polymers exhibited rather stable poled structures after electric poling, possibly owing to the helical structures of PLG. Aromatic polymers such as poly(p-phenylene) are thermally stable with high glass transition temperatures. Poly(p-phenylene) derivatives having various donor or acceptor groups were used to measure NLO properties in terms of SHG and third harmonic generations (THG). They showed high SH coefficients with less relaxation behaviors of the poled structures.

A new tetracationic cyclophane, cyclobis(4,4′-azopyridinium-p-phenylene) (2·4PF6), was synthesized via template-directed synthesis and characterized by MS and NMR spectroscopy. For the preparation of π-electron-deficient 2·4PF6, the use of π-electron-rich templates such as 1,4-bis[2-(2-hydroxyethoxy)ethoxy]benzene (4) and 1,5-bis[2-(2-hydroxyethoxy)ethoxy]naphthalene (5) enhanced the cyclophane formation in 17 and 19% yields, respectively. 1H NMR spectra of the reaction mixture revealed that the cyclophane precursor 1·2PF6 formed supramolecular assembling complexes with hydroquinone derivatives 4 and 5 before the ring formation. The intermolecular charge transfer interaction and the stability constants (Ka) of complexes generated between the electron-acceptor 2·4PF6, and electron-donors 1,4-dimethoxybenzene 3, 4, and 5 were evaluated using UV-vis, spectroscopy and spectroscopic titration. The absorption bands attributable to CT interactions were centred at 580 nm for 3, 635 nm for 4, and 646 nm for 5, with stability constants of 17±2, 2100±200, and 2400±300, respectively.

Radical copolymerization of 2-(N,N-dimethyl)aminoethyl methacrylate (1) and acrylonitrile (2) initiated by 2,2'-azobis(2-methylpropionitrile) was carried out. The sequence distributions of the copolymers were investigated by C-13 NMR spectroscopy. A terminal model was used to interpret the propagation process in the copolymerization. The monomer reactivity ratios in the bulk copolymerization at 45 degrees C were evaluated as r(1) = 1.06 and r(2) = 0.07. Radical reactivity indices and frontier electron densities for 1 and 2 were calculated.

New bisaxially coordinated phthalocyanines metal compounds were synthesized by melting azopyridines and phthalocyaninato metals such as phthalocyaninato iron (II) and phthalocyaninato cobalt (II). These complexes were characterized by using NMR, FT-IR, UV-Vis spectra, and TG/DTA.

New ion conductive polymer complexes were formed by dissolving various polycation salts into room temperature molten salts containing aluminium chloride. The viscoelastic films were fabricated from the molten salts added at least 10 mol % of the polypyridinium salts. The ionic conductivities of the polymer complexes were 10-100 times higher than poly(ethyleneoxide)-based polymers at room temperature and were affected by their composition.

Azopyridinium methylsulfates were systematically prepared and their electrochemical and photochromic properties were evaluated by using UV spectroscopy and cyclic voltammetry. Some azopyridiniums were newly identified as photochromic compounds.

Langmuir-Blodgett (LB) films were fabricated from mixtures of poly(bromooctylthiophene-co-vinylhexylthiophene) (PVHT copolymer) and deuterated stearic acid (d-SA). The molecular orientation of the mixed LB films was studied by measuring surface pressure-area isotherms of the monolayers and visible absorption spectra, X-ray diffraction patterns, and FT-IR spectra of multilayer thin films. The FT-IR transmission and grazing angle reflection spectra exhibited a strong polarization dependence, allowing an estimation of the tilt angles of the hydrocarbon chain axis for both the d-SA molecules and the PVHT copolymer. The main chains of the copolymer were found to be randomly distributed within the film, whereas the hydrocarbon tails of the d-SA molecules and the PVHT copolymer were found to be oriented nearly perpendicular to the film surface. The mixed LB films were rendered electrically conductive (2S cm(-1)) by doping with NOPF6, and FeCl3.

Langmuir-Blodgett monolayer and multilayer films were formed from nickel tetra-tert-butylphthalocyanine, iron tetra-tert-butylphthalocyanine, and mixtures of these phthalocyanines with poly(3-hexylthiophene). In the mixed films, the phthalocyanine molecules serve as both a surface-active agent to promote spreading and an electroactive material. The structures of the resultant LB films were investigated by using optical absorption spectroscopy, FTIR spectroscopy, and low-angle X-ray diffraction. In the mixed LB films, the nickel phthalocyanine molecules were found to stack in one-dimensional arrays with their rings oriented essentially perpendicular to the substrate surface. The mixed iron phthalocyanine LB films, on the other hand, were comprised of both one-dimensional arrays and randomly oriented rings due to a stronger intermolecular interaction developed between the poly(3-hexylthiophene) and iron phthalocyanine molecules. In both cases, the PHT-conjugated chains were found to be oriented nearly parallel to the substrate. The multilayer films of these systems were rendered electrically conductive by doping with I2 or SbCl5. Conductivities in the range of 10(-1)-10(-6) S cm-1 were observed in the doped films.

Composites of elastomeric polymers and poly(gamma-methyl L-glutamate) (PMLG) were prepared by the so-called ''in-situ polycondensation method'' and a solution blend method. Three types of rubbers were used as matrix polymers:styrene-butadiene copolymer and two derivatives. Mechanical properties of these composite polymers were studied by tensile tests and their morphologies were observed by scanning electron microscopy. The tensile strength and modulus of the composite films obtained by the in-situ polycondensation method increased with increasing PMLG content. Although their tensile modulus values increased drastically, their ultimate elongation values were almost the same. The morphologies of the composites and the reinforcing effect of PMLG were dependent on the preparation method, on the contents of PMLG, and on an interaction between matrix polymer and PMLG.

Multicomponent Langmuir-Blodgett (LB) films containing polypyrrole, 3-octadecanoyl pyrrole, and poly(3-hexylthiophene) were fabricated via a novel in-situ polymerization process. In this process, pyrrole monomer is polymerized at the air-subphase interface in the presence of poly(3-hexylthiophene) by using a subphase containing 1 wt% FeCl3. The resultant electrically conductive films could be readily deposited onto solid substrates as Z-type films by the vertical lifting method. By using visible absorption, x-ray diffraction, and FTIR measurements, it was found that all three components were present within the transferred films, with the polypyrrole chains assuming a preferential orientation parallel to the film surface. The conductivities of the mixed LB films were as high as 1.0 S/cm, and the stability of the conductivity was very good. Chemical doping of poly(3-hexylthiophene) within the film with strong oxidizing agents such as I2 further enhanced the conductivity of the film.

Radical polymerization reaction of styrene was carried out in mixed solvents of ethanol and n-hexane in the presence of poly(methyl vinyl ether) (PMVE) which was used as a matrix polymer to control its morphology in the polymer solution where styrene monomer might be concentrated. Size and dispersity of the resulting polystyrene microspheres could be controlled by changing morphology of the matrix polymer which was caused by the ratio of ethanol to n-hexane.

Poly(L-lysine-sebacic acid) (PLS) and poly(L-lysine-terephtalic acid) (PLP) were synthesized by the low temperature polycondensations of sebacoyl chloride or terephthaloyl chloride with N,N'-bis(trimethylyl)-L-lysine-ethyl ester (TMSL), respectively. Hydrolytic and enzymatic degradation of PLS and PLP films were investigated by the determination of the weight loss, mechanical properties of their films, and SEM. The rate of enzymatic degradations of PLS films were found to be much higher than those of its hydrolytic degradation. However, the rate of enzymatic degradation of PLP films was the same as that of its hydrolytic degradation, and lower than that of PLS films. These results indicate that the aliphatic polyamide containing L-lysine is a biodegradable polymer.

The influence that various doping treatments have on the molecular structure and organization of mixed Langmuir-Blodgett films comprised of poly(3-hexylthiophene) and deuterated stearic acid was investigated using reflection-absorption infrared spectroscopy. The molecular organization and electrical properties of these films were found to depend strongly on the type of dopant used and its method of introduction. When doped from solution with NOPF6 and SbCl5, the original molecular organization of the multilayer film was significantly disrupted and the deuterated stearic acid molecules were extracted into the doping solution. In some cases, this extraction process produced uniform thin films of poly(3-hexylthiophene) with conductivities comparable to free-standing films. Gas-phase doping with I2 and SbCl5, on the other hand, could be accomplished without significantly altering the molecular morphology of the film. The heterogeneous two-phase nature of the multilayer films in this case resulted in lower conductivities.

Langmuir-Blodgett monolayer and multilayer thin films were formed from nickel tetra-tert-butyl phthalocyanine and mixtures of this molecule with poly(3-hexylthiophene). In the mixed system, the phthalocyanine molecules serve as both a surface active agent to promote spreading and an electroactive material. The phthalocyanine rings exhibited a tendency to be stacked in one-dimensional arrays and oriented essentially perpendicular to the substrate, while the poly(3-hexylthiophene) molecules were found to be oriented nearly parallel to the substrate. The multilayer films of this system were rendered electrically conductive by doping with I2 or SbCl5. Conductivities in the range of 10(-2) - 10(-3) S cm-1 were observed in films containing a 5:1 mole ratio of poly(3-hexylthiophene) to phthalocyanine.

The fabrication of Langmuir-Blodgett (LB) thin films containing electroactive conjugated polymers has been accomplished using a variety of new techniques. In one case, monolayer forming polyion complexes have been formed from acid derivatized conjugated polymers and stearylamine. Alternatively, stable, mixed monolayers containing a surface active processing aid and the emeraldine base form of polyaniline were successfully manipulated into multilayer thin films. Another variation involved the in situ formation of electrically conductive chains of polypyrrole within a preformed multilayer thin film of ferric stearate. The resultant multilayer films exhibited well defined molecular organizations and achieved electrical conductivities in some cases as high as 5 S/cm.

Langmuir-Blodgett multilayer thin films were fabricated from mixed monolayers containing poly(3-hexyl thiophene) and 3-octadecanoyl pyrrole. The mixed monolayers were found to be stable at the air-water interface and could be readily deposited onto solid substrates as Y-type films by the vertical lifting method. The structure of the mixed multilayer thin films was probed by visible absorption, thickness, X-ray diffraction, and FTIR measurements. Evidence for preferential orientation of both the polymer chains and the surface active molecules was found. The conductivities of the mixed LB films doped with strong oxidizing agents such as NOPF6, FeCl3, H2PtCl6 and SbCl5 were in the range of 10(-3)-1.0 S/cm. The temperature dependence of the conductivity was found to fit a logs varies as T-1/2 dependence.