Published papers

The adduct formation of iron(III) chlorophyll a with phosphines or phosphites has been studied by spectroscopic methods. The red-shift in the Soret and Q bands caused by the axial coordination of phosphine or phosphite to iron(III) chlorophyll a is an evidence for the autoreduction of the central iron(III) ion. The 31P{1H} NMR spectrum of bis-adducts measured in the presence of excess phosphine or phosphite ligands gave a single peak in the down field range compared to that of the corresponding free ligand. The ESR and X-ray photoelectron spectra have revealed that the central iron atom of the bis-adduct of iron chlorophyll a with phosphines or phosphites is divalent and in the low-spin state. The axial coordination of phosphine or phosphite influences the electronic configuration of the central iron atom and the macrocyclic chlorine ligand to induce the autoreduction of the central iron(III) ion.

Two kinds of iron chlorophylls, i.e. (methyl pyropheophorbide a)iron(III) chloride and its bis-pyridine adduct, were prepared and characterized by57Fe Mössbauer spectroscopy. (Methyl pyropheophorbide a)iron(III) chloride gave an asymmetric quadrupole-split doublet typical of high-spin iron(III) chlorophylls, while its bis-pyridine adduct showed a symmetric quadrupole-split doublet characteristic of low-spin iron(II) chlorophylls. The isomer shift and quadrupole splitting obtained for (methyl pyropheophorbide a)iron(III) chloride and its bis-pyridine adduct have led to the following conclusions. The substitution of the bulky phytyl group for the methyl group hardly affects the electronic state of the iron(II,III) ion, but the elimination of the methoxycarbonyl group increases the planarity of the macrocyclic chlorin ligand.

The influence of distortion in the porphine ring on the electronic structure of the central metal ion was studied by means of the ESR spectra of copper(II) chlorophylls. A linear correlation between ESR parameters, i.e. g and A values, indicated that the electronic structure of the central copper(II) ion in CuChls is different from that in compounds having the regular porphine skeleton. The weakened CuN bond in CuChls was evidenced by a decrease in the bonding coefficient α2. These observations on the ESR parameters of CuChls were explained by a partially saturated and distorted macrocyclic structure.

Copper(II) chlorophyllin, consisting of copper(II) pheophorbide a, copper(II) chlorin e6, copper(II) rhodin g7 and copper (II) chlorin e4, was prepared and separated by semi-preparative high-performance liquid chromatography (HPLC). The components of copper(II) chlorophyllin were determined on a reversed-phase Inertsil ODS-2 column using a mobile phase of methanol-water (97:3, v/v) containing 1% (v/v) of acetic acid. Linear calibration plots were obtained for copper(II) chlorophyllin in the concentration range of 0–30 μg cm−3 with photometric detection at 407 or 423 nm. The detection limits of copper(II) pheophorbide a, copper(II) chlorin e6, copper(II) rhodin g7 and copper(II) chlorin e4 were 3.5, 1.5, 3.3 and 1.4 ng cm−3 with relative standard deviations (n = 10) of 1.8, 1.6, 5.2 and 3.6%, respectively. The reversed-phase HPLC method proposed here was demonstrated to be useful for the determination of the components of sodium copper(II) chlorophyllin.

he electronic states of open-shell stilbene diradicals were studied. Previously used semiempirical MO-CI methods were applied to stilbenes having dimethylene, dioxyl, and dinitroxide centers in o,o′-, o,m′-, o,p′-, m,m′-, m,p′-, and p,p′-substitution patterns, and the various singlet-triplet energy gaps were computed to predict qualitative ground state spin multiplicities. Singlet and triplet spin states were essentially degenerate in the m,m′-isomers of disjoint connectivity, while nondisjoint o,m′- and m,p′-isomers had triplet computed ground states. Nitroxide-based diradicals showed considerably smaller computational exchange coupling energies than did other diradical models studied. As a tests of these computations, stilbenes with two N-tert-butyl nitroxide groups at the o,m′-, m,m′-, and m,p′-positions were prepared, and their magnetic properties were studied by ESR and magnetic susceptibility measurements. The m,m′- and m,p′-isomers were found experimentally to have singlet and triplet ground states, respectively, in accord with the qualitative computed predictions.

The magnetic properties of poly(phenylacetylene)s with radical groups at the paraposition, poly[(3,5-di-tert-butyl-4-oxyphenyl)acetylene] (l),poly[[4-[(3,5-di-tert-butyl-4-oxyphenyl)(3,5-di-tert-butyl4-oxocyclohexa-2,5-dien-l-ylidene)methyl]phenyl]acetylene](2) and poly[[4-(N-tert-butyl-N-oxyamino)-phenyl]acetylene](3), were studied with a SQUID magnetometer. The magnetization and magnetic susceptibility indicated unexpected antiferromagnetic interactions between the radical sites. The exchange interaction observed in these conjugated polyradicals was discussed in connection with their computationally modeled structures.

Intramolecular and intermolecular exchange in molecules and polymers is investigated computationally and experimentally, in order to identify structure-property relationships. Theory and Experiment of Investigation of Exchange Interactions in Organic Molecules and Materials.

Poly(phenylvinylene) and poly(phenylenevinylene) with tert-butyInitroxide as a built-in radical group were synthesized. Precursor polymers were obtained by the polymerization of the corresponding acetylene and styrene derivatives by Rh and Pd catalysts. They were soluble in common solvents and their chemical oxidation under moderate condition gave the corresponding polyradicals.

[4-(N-tert-Butyl-N-hydroxyamino)phenyl]acetylene (7) was synthesized and polymerized to yield a solvent-soluble polyacetylene: poly [[4-(N-tert-butyl-N-hydroxyamino)phenyl] acetylene] (8). Oxidation of the polymer gave its radical derivative: the ESR spectrum showed a broad signal only in the delta ms = ±1 region, and magnetic measurement with a SQUID magnetometer revealed an antiferromagnetic through space interaction.

The polymerization behavior and photoinitiation process in the visible light‐cured dental composite resins were studied using ESR and IR spectroscopies. The concentration of methacryl propagating radical corresponded to the transmittance of irradiated light. While the radical was stable and long‐lived in the cured resin, its concentration quickly decreased in the oral cavity due to the ventilation of atmospheric oxygen accompanied by respiration. Camphorquinone radical in the presence of tertiary amine easily initiated the radical polymerization. A decrease in monomer consumption was explained by the inhibition effect of oxygen in the photoinitiation process. Post‐curing by the residual radical proceeded effectively in the deeper part of the resin.

m- and p Bis(diphenylene)propenylphenylacetylene (m-, p-8) were synthesized and polymerized with WCI6, MoCl5, and Rh catalyst, yielding solvent-soluble poly(phenylacetylene)s bearing a π-conjugated bis(di-phenylene)propenyl groups (m-, p-7a). The polymers gave their polyanion derivatives, which were electrolytically and chemically oxidized to yield the corresponding polyradicals (m-, p-7b). The polyradicals were chemically very stable due to the resonance stabilization of an unpaired electron whose spin concentration could be increased up to ca. 2 × 1023 spins per molar monomer unit. ESR spectroscopy suggested an antiferro-magnetic interaction between unpaired electrons.

[4-[(3,5-Di-tert-butyl-4-hydroxyphenyl) (3,5-di-tert-butyl -4-oxocyclohexa-2,5-dien-1-ylidene) -methyl]pheny l ]acetylene (6), was synthesized and polymerized to yield a solvent-soluble polyacetylene poly-[[4-[3,5-di-tert -butyl-4-hydroxyphenyl) (3,5-di-tert-butyl-4 -oxocyclohexa-2,5-dien-1-ylidene) methyl]phenyl ] acetylene] (5a). The polymer gave its polyradical derivative 5b through the chemical oxidation with active PbO2. 5b was stable, whose spin concentration could be increased up to 4.8 × 1023 spins per molar monomer unit. ESR analysis indicated localization of unpaired electrons in the galvinoxyl residue. ESR analysis also suggested an exchange-narrowing and interpolymer dipole-dipole interaction.

光硬化型歯科用コンポジットレジン中のアクリレートモノマーの重合挙動を, 硬化体中に残存するラジカル濃度とモノマー二重結合のESR及びIR定量から考察した. 光照射により硬化体中にはメタクリル生長ラジカルが検出され, その濃度は光到達度に対応した. 生長ラジカルは極めて安定に硬化体中に残存したが, 温度が高く換気十分な口腔内では速やかに減少した. 一方, モノマー二重結合消費率は硬化体表面では酸素により, また深部では低い光透過により減少した. 重合率の経時変化から, 残存ラジカル種の後反応によって硬化体深部で重合が進行し, 硬度が維持されていることが示された.

Luminescence properties of Tb3+ - or Eu3+-polycarboxylate complexes in aqueous solution were investigated. The excitation bands near 300 nm for terbium- or europium-polyacrylate solutions were drastically enhanced by the addition of hydroxyl-radical generating reagents as well as ultrasonic irradiation. These spectral changes were attributed to the energy transfer from chromophore molecules formed by the hydroxyl radicals generated in both systems.

(3,5-Di-tert-butyl-4-hydroxyphenyl)acetylene (8) was synthesized and polymerized with WCIs and MoCl5, giving a novel and solvent-soluble conjugated polymer, poly[(3,5-di-tert-butyl-4-hydroxyphenyl)acetylene] (3). Visible absorption of the polymer indicated a fairly long π-conjugated system along the main chain. The polymer yielded its polyanion 10 and polyradical derivative 4 after the treatment of its solution with an alkali and oxidizing reagent, respectively. The polyradical 4 was surprisingly stable, and spin concentration was increased up to 2.3 × 1023 spins/molar (hydroxyphenyl)acetylene residue. ESR spectra of the polyradical 4 in solution suggested that the formed unpaired electrons were delocalized along the polyacetylene main chain. 4 was also very stable even in solid state. Spin-exchange interaction observed in 4 strongly depended on its spin concentration. Antiferromagnetic interaction between the unpaired electrons was suggested from the temperature dependency of the ESR signal intensity.

ynthesis and magnetic properties of π-conjugated stable polyradicals bearing a polyacetylene backbone are described. 2,6-Di-tert-butyl-4-ethynylphenol (8) and 4-ethynylphenylhydrogalvinoxyl (9) are polymerized with W, Mo chloride or Rh complex to yield their polyacetylene derivatives with molecular weight of ca. 10^4, while 2-ethynylphenalenone (10) gives only its oligomer. The polymers are soluble in common solvents and converted to the corresponding conjugated polyradicals via heterogeneous chemical oxidation using PbO2 or alkaline K3Fe(CN)6. The polyradicals with extremely high spin concentration (up to 4.8 × 10^23 spins/monomer mol) are obtained by regulating the oxidative conditions. The polyradicals are quite stable in solution and even in the solid state because of resonance stabilization and/or a steric effect of the substituents. Magnetic interactions between the unpaired spins in the conjugated stable polyradicals are discussed.

側鎖に安定有機ラジカルを有するポリアセチレンの光電子スペクトルの解析結果について報告した。

Formation and magnetic properties of ?r-conjugated phenoxy radicals bearing a porphyrin macrocycle or a polyacetylenic backbone are described. Tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)porphinatometals (7-M) [M = Zn(II), VO(II), and Cu(II)] were oxidized to give the corresponding stable monoradical and biradical. Magnetic properties of the radical species depend on the magnetic orbital of the central metal ion. ESR hfs structure reveals that the biradical for 7-Zn and -VO are in the triplet (S = 1) and quartet state (S = 3/2), respectively. Poly(3,5-di-t-butyl-4-hydroxyphenylacetylene) (8) and poly(pethynylphenylhydrogalvinoxy1) (9) with molecular weights of %lo4 are characterized. ESR spectra with hyperfine structure for 8 indicate that the phenoxy radicals are conjugated with the polyacetylenic main chain over ~7 monomer units as a“neutral soliton.” Formed polyradicals for 8 and 9 are surprisingly stable, even in the solid state, due to resonance stabilization and/or steric effect of the conjugated main chain. An antiferromagnetic interaction is observed for oxidized 8 with a spin concentration above 10 mol%.

This paper describes the synthesis of poly-[4-[(3,5-di-tert-butyl-4-hydroxyphenyl) (3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-yldene) methyl]phenylacetylene] (abbreviated as poly[(p-ethylphenyl)hydrogalvinoxyl]) (4) and also the formation of its polyradical macromolecule, 5, through chemical oxidation. 5 is one of the model polymers with an indirect magnetic interaction; the unpaired electron is mainly localized at the phenylgalvinoxyl side chain, whose spin density is distributed mainly over the galvinoxyl substituent, but also over the phenyl ring to some extent by a spin polarization mechanism.

Electronic state and magnetic interaction of π-conjugated phenoxy radicals bearing a polyacetylenic backborn are described. Poly(3,5-di-t-butyl-4-hydroxyphenylacetylene) (7a) and poly(p-ethynyl-phenylhydrogalvinoxyl) (8a) with molecular weight ca. 10^4 are characterized. ESR spectra with hyperfine structure for the chemically oxidized 7b indicate that the phenoxy radical conjugates through the polyacetylenic main chain over ca. 7 monomer units as a “neutral soliton.” Polyradicals 7b and 8b are surprisingly stable even in the solid state, because of a resonance stabilization and/or a steric effect of the conjugated main chain. An antiferromagnetic interaction is observed for 7b with spin concentration above 10 mol%. Mechanism of the magnetic interaction is discussed.