Takashi Kaneko

FT Pulsed ESR/Electron Spin Transient Nutation (ESTN) Spec-Troscopy Applied to High-Spin Systems in Solids; Direct Evi-Dence of a Topologically Controlled High-Spin Polymer as Models for Quasi ID Organic Ferro-and Superpara-Magnets

Abstract FT Pulsed ESR/Electron Spin Transient Nutation(ESTN) Spectroscopy has been, for the first time, extended to amorphous and powder states of materials. Recently, organic high-spin polymers and clusters have emerged. With the increasing molecular spin quantum number S and molecular weight of the polymers, cw ESR spectroscopy manifests its inherent disadvantages in discriminating high spins from S=½ and in determining the Ss for the complex mixture of various spin assemblages. An electron spin transient nutation (ESTN) method based on pulsed ESR spectroscopy has been for the first time applied to a quasi 1D neutral high-spin polymers (A) as one of the most complex amorphous spin assemblages, identifying that the first neutral high-spin polymer A is comprised of high-spin assemblages characterized by the even Ss greater than ½. The molecular quantum spin number S have been identified up to S=4, showing direct evidence of the occurrence of a high-spin polymer with a π-topologically controlled spin po...

Polyacetylene derivatives with chain-sided phenoxy and galvinoxyl radicals

Abstract Polyacetylene derivatives bearing chain-sided, π-conjugated and bult-in phenoxy radicals were synthesized. They were soluble in common solvents and gave a transparent thin-film. ESR indicated partial deloalization of the unpaired electron generated in the chain-sided group into the main chain. But any ferromagnetic interaction between the spins could not be observed.

Poly(Phenylvinylene) and Poly(Phenylene-Vinylene) with Nitroxide Radicals

Abstract 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.

FT Pulsed ESR/Electron Spin Transient Nutation Spectroscopy in the Study of Molecular Based Magnetism: Applications to High-Spin Polymers and Ferromagnetic Materials

Abstract Recently, organic high-spin polymers and clusters have been emerging. With the increasing effective molecular spin quantum number S and molecular weight of the polymers, however, cw ESR spectroscopy manifests its inherent disadvantages in discriminating high spins from S=½ and in determining the Ss for the complex mixture of various spin assemblages. An electron spin transient nutation method based on pulsed ESR spectroscopy has been for the first time applied to a quasi 1D high-spin polymer as one of the most complex amorphous spin assemblages, identifying that the polymer is comprised of high-spin assemblages with the Ss greater than two. It can be concluded that electron spin transient nutation spectroscopy is a facile and useful method for the exclusive identification of S and ESR transitions even for the cases of apparently vanishing fine-structure splittings and for spin systems with residual fine-structure terms in the spin Hamiltonian. Fundamental bases for the transient nutation method...

New Aspects of High-Spin Chemistry

Abstract As a novel high-spin molecule, a through-bond spin-frustrated organic molecule 4,4′,4Prime;-trisdiphenylmethyleneamine (TDMA) and its anion and cation was studied by cw-ESR spectroscopy. TDMA is a spin frustrated system composed of three S=1 units coupled antiferromagnetically. This molecule was shown to have a triplet ground-state which is asymmetrical in its exchange interaction as well as its molecular conformation. The TDMA ions were generated at low temperature via successive radiolysis and photolysis of its diazo precursor. It was shown that the ground states of the anion and cation are quartet and sextet, respectively. This means that upon ionization the ground state changed from the intermediate-spin state of TDMA to the high-spin state of the ions, showing the interrelation between spin alignment and excess charge in a molecular field. On the other hand, in order to identify and discriminate the spin multiplicities of complicated spin assemblages in amorphous materials, we have developed...

π-conjugated polyradicals with poly(phenylene-vinylene) skeleton and their through-bond and long-range interaction

Abstract The poly(phenylenevinylene) skeleton was selected as a magnetic coupler of polyradicals, because of its developed π-conjugation, coplanarity, and solvent-solubility even after substitution on the phenylene ring. By synthesizing poly(1,4- or 1,2-phenylenevinylene)-2- or -4-substituted with a stable phenoxy or nitroxy radical, an intramolecular, through-bond and long-range, but strong, ferromagnetic exchange interaction was realized for the first time. The polyradicals were chemically stable and, even at their spin concentration of ca. 0.5, displayed S values of 2/2 ∼ 4/2.

FT Pulsed ESR/ESTN(Electron Spin Transient Nutation) Spectroscopy Applied to High-Spin Systems

Organic molecular based magnetism (abbreviated to organic magnetism) [1,2] has found ever increasing interest from both the pure and applied sciences for last decade [3a–c]. The conceptual proposals of organic magnetism were made at early times [1,2]. A rapid development of this research field partly is due to the rich variety of novel physical phenomena and properties which synthetic organomagnetic materials are expected to exhibit both macro- and meso-scopically and partly due to their underlying potential applications as future technology in materials science [4,5].

Poly[(N-oxyamino) and (oxyphenyl)phenylenevinylene]s: Magnetically coupled polyradicals in the chain

Abstract Poly(phenylenevinylene)s with built-in radical groups are expected to show magnetic interaction caused by spin polarization and/or coplanarity of the π-conjugated chain. Diradical models for the poly(phenylenevinyllene)- based polyradicals were synthesized, and the magnetic properties were discussed based on ESR spectra and magnetic measurement. Magnetization and magnetic susceptibilities of the polyradicals, tert-butylnitroxyl- and 2,6-di-tert-butylphenoxyl-substituted poly(1,2- or 1,4-phenylenevinylene), indicated the occurrence of ferromagnetic interaction corresponding to these oligomeric diradicals.

Synthesis and magnetic properties of conjugated stable polyradicals

Abstract Synthesis 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. 104, 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 × 1023 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.