Upward temperature shift of the intrinsic phase lag of the magnetization of Bis(phthalocyaninato)terbium by ligand oxidation creating an S = 1/2 spin

An alternating-current (ac) magnetic susceptibility measurement for the [(Pc)(2)Tb(III)](0) complex (Pc = phthalocyaninato) has shown that ligand oxidation of the anionic [(Pc)(2)Tb(III)](-) complex gives rise to a significant upward shift of the temperature range where the magnetization response shows a phase lag behind the time-varying external magnetic field. The peaks of the out-of-phase component of the ac susceptibility of the pi-radical [(Pc)(2)Tb(III)](0) were observed at 50, 43, and 36 K with ac magnetic fields of 10(3), 10(2), and 10 Hz, respectively, which were more than 10 K higher than the corresponding values of the anionic complex with a closed-shell pi-system. The ac susceptibility measurements on the complex with octa(dodecoxy)-substituted Pc ligand, which is readily dilutable in diamagnetic media, proved that the significant rise of the temperatures occurs as an intrinsic single-molecular property of the complex possessing both J = 6 and S = (1)/(2) systems, and is not due to long-range magnetic order or interactions between adjacent unpaired pi-electrons.     

Birefringence control by hydrogen bonding on compatible polymer pair composed of hydrogenated ring‐opening polymer and modified polystyrene

A new polymer blend composed of a hydrogenated ring‐opening polymer (HROP) with an ester group and hydroxyl functionalized polystyrene (HFP) produced the excellent transparent materials which enabled a precise birefringence control in keeping with the other physical properties for optical film use. The blend with a composition from 0.28 to 0.35 for the HFP weight fraction showed an extraordinary wavelength dispersion, transmitting through a zero birefringence point at the critical fraction of 0.45, while each polymer showed an ordinary wavelength dispersion. The observed excellent transparency even above those of the glass transition temperature was attributed to a depressed phase separation that resulted from strong hydrogen bond between the ester and hydroxyl groups. An IR analysis of the film demonstrated a remarkable red‐shift in the carbonyl peak with an increase of the hydroxylated polystyrene content, indicating a strong hydrogen bond between those groups. This new polymer blend provides a useful design to achieve practical demands for film use, both optical and mechanical under the fabrication conditions using the melt extrusion technique. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3132–3143     

Effect of discrete track medium at high areal density

The degradation of SNR caused by the higher uniaxial crystalline anisotropy field (Hk) of medium and small write fields of narrower write width is one of the problems for achieving higher areal density. The SNR dependence on Hk of a medium with different write fields of head using the discrete track medium (DTM) is investigated by using micromagnetics simulation. As a result, the curves of SNR as a function of Hk have peak values. In DTM, the peak values of SNR are almost constant at any Hk of the medium and different write fields. Higher SNR is realized even at low Hk and small write field in DTM.     

Static magnetic-field-induced phase lag in the magnetization response of tris(dipicolinato)lanthanides

Alternating-current (ac) magnetic susceptibility measurements for tris(dipicolinato) complexes with a trivalent heavy lanthanide ion, [N(C2H5)4]3[Ln(dipic)(3)] x nH2O (dipic = pyridine-2,6-dicarboxylate; Ln = Tb, Dy, Ho, Er, Tm, or Yb) are reported. While none of the six complexes showed a magnetization lag from the ac magnetic field of 10-10(3) Hz above 1.8 K, the Dy, Er, and Yb complexes with odd numbers of 4f electrons exhibited the magnetization lag in a static magnetic field. This phenomenon is explained to be caused by the elimination of a fast relaxation path, which is only effective for the Kramers doublet ground states in near zero field. At higher static fields, the remaining paths such as Orbach and/or direct processes govern the dynamics of the two-level systems comprised of spin-up and spin-down states. The non-Kramers complexes were found to have a nondegenerate ground state with large energy gaps from higher states, which is consistent with their fast magnetization relaxation.     

Direct observation of hydrogen-bond exchange within a single water dimer

The dynamics of water dimers was investigated at the single-molecule level by using a scanning tunneling microscope. The two molecules in a water dimer, bound on a Cu(110) surface at 6 K, were observed to exchange their roles as hydrogen-bond donor and acceptor via hydrogen-bond rearrangement. The interchange rate is approximately 60 times higher for (H2O)2 than for (D2O)2, suggesting that quantum tunneling is involved in the process. The interchange rate is enhanced upon excitation of the intermolecular mode that correlates with the reaction coordinate.     

Time-resolved EPR spectra of a photoexcited phenanthrene-linked copper(II)-free-base porphyrin dimer: An intermediate-coupling case in a triplet-doublet spin system

Time-resolved electron paramagnetic resonance (TREPR) spectra are presented for a phenanthrene-linked copper(II)-free-base porphyrin dimer. In the lowest electronic excited state, the free-base half is in the (π, π*) triplet state and the copper-porphyrin half is in the doublet ground state due to the copper(II) spin. Because of the interaction between the triplet and doublet spins, the excited state of the dimer is described as a coupled triplet-doublet pair state. By choosing the excitation wavelength, this coupled state is produced via either the intersystem crossing within the free base or the energy transfer from the excited state of the copper porphyrin. The observed TREPR spectra show very large spectral widths compared to that of the triplet state in the free-base monomer. In addition, there is a prominent absorptive band in the center of the spectra regardless of the generation pathway. These features can be interpreted as characteristic properties in an intermediate-coupling case, where the degree of the triplet and doublet mixing largely depends on the molecular orientation relative to the magnetic field.     

Determination of ligand-field parameters and f-electronic structures of double-decker bis(phthalocyaninato)lanthanide complexes

The f-electronic structures of the ground states of anionic bis(phthalocyaninato)lanthanides, [Pc(2)Ln](-) (Pc = dianion of phthalocyanine, Ln = Tb(3+), Dy(3+), Ho(3+), Er(3+), Tm(3+), or Yb(3+)), are determined. Magnetic susceptibilities of the powder samples of [Pc(2)Ln]TBA (TBA = tetra-n-butylammonium cation) in the range 1.8-300 K showed characteristic temperature dependences which resulted from splittings of the ground-state multiplets. NMR signals for the two kinds of protons on the Pc rings at room temperature were shifted to lower frequency with respect to the diamagnetic Y complex in Ln = Tb, Dy, and Ho cases, and to higher frequency in Er, Tm, and Yb cases. The ratios of the paramagnetic shifts of the two positions were near constant in the six cases. This indicates that the shifts are predominantly caused by the magnetic dipolar term, which is determined by the anisotropy of the magnetic susceptibility of the lanthanide ion. Using a multidimensional nonlinear minimization algorithm, we determined a set of ligand-field parameters that reproduces both the NMR and the magnetic susceptibility data of the six complexes simultaneously. Each ligand-field parameter was assumed to be a linear function of atomic number of the lanthanide. The energies and wave functions of the sublevels of the multiplets are presented. Temperature dependences of anisotropies in the magnetic susceptibilities are theoretically predicted for the six complexes.     

Interaction between f-electronic systems in dinuclear lanthanide complexes with phthalocyanines

The first detection and characterization of the interactions between the f-electronic systems in the dinuclear complexes of paramagnetic trivalent Tb, Dy, Ho, Er, Tm, and Yb ions with phthalocyanine ligands are presented. The molar magnetic susceptibilities, chi(m), were measured for PcLnPcLnPc* ([Ln, Ln]; Pc = dianion of phthalocyanine, Pc* = dianion of 2,3,9,10,16,17,23,24-octabutoxyphthalocyanine) and PcLnPcYPc* ([Ln, Y]) in the range from 1.8 K to room temperature. The selective synthetic method previously reported for the heterodinuclear complex [Y, Ln] was used to prepare [Ln, Ln] and [Ln, Y] with a modification on the choice of starting materials. The f-f interaction contributions to the magnetic susceptibility are evaluated as Delta(chi)(m)T = chi(m)([Ln, Ln])T - chi(m)([Ln, Y])T - chi(m)([Y, Ln])T, where T refers to temperature on the kelvin scale. The homodinuclear complexes having f(8)-f(10)-systems, namely [Tb, Tb], [Dy, Dy], and [Ho, Ho], show positive Delta(chi)(m)T values in the 1.8-50 K range, indicating the existence of ferromagnetic interaction between the f-systems. The magnitude of the Delta(chi)(m)T increases in the descending order of the number of f-electrons. [Er, Er] gives negative Delta(chi)(m)T values in the 1.8-50 K range, showing the antiferromagnetic nature of the f-f interaction. [Tm, Tm] exhibits small and negative Delta(chi)(m)T values, which gradually decline in the negative direction as the temperature decreases in the range 13-50 K and sharply rise in the positive direction as the temperature falls from 10 to 1.8 K. [Yb, Yb] has extremely small Delta(chi)(m)T values, whose magnitude at 2 K is less than 1% of that of [Tb, Tb]. The ligand field parameters of the ground-state multiplets of the six [Ln, Y] complexes are determined by simultaneous fitting to both the magnetic susceptibility data and paramagnetic shifts of (1)H NMR. The theoretical analysis successfully converged by assuming that each ligand field parameter is a function of the number of f-electrons in each ion. Using these parameters as well as the previously obtained corresponding parameters for the [Y, Ln] series, the interactions between the f-systems in [Ln, Ln] are investigated. All the characteristic observations above are satisfactorily reproduced with the assumption that the magnetic dipolar term is the sole source of the f-f interaction.