27860-55-5Relevant academic research and scientific papers
Light-induced electron spin polarization in vanadyl octaethylporphyrin: I. Characterization of the excited quartet state
Kandrashkin, Yuri E.,Asano, Motoko S.,Van Der Est, Art
, p. 9607 - 9616 (2006)
Laser flash induced spin-polarized transient electron paramagnetic resonance (TREPR) spectra for vanadyl octaethylporphyrin in isotropic and partially ordered frozen solutions are presented and compared with corresponding luminescence data. The TREPR spectra show well-resolved hyperfine couplings to the vanadium nucleus and a multiplet polarization pattern with features typical of zero-field splitting (ZFS). The principal values of the vanadium hyperfine coupling tensor evaluated from the spectra are 1/3 of the corresponding values found from steady-state EPR spectra of the ground state. On the basis of these characteristics and numerical simulations, the polarization patterns are assigned to the excited quartet state. The values of the ZFS parameters of the trip-quartet obtained from simulation of the spectra (D = 17.5 mT and E = 1.5 mT) are comparable to those of the triplet state of the zinc and free base octaethyl porphyrin. The lifetime of the spin polarization is found to be temperature dependent and is essentially the same as that of the optical emission. The temperature dependence is rationalized using a model in which the decay to the ground state occurs from both the trip-quartet and trip-doublet, which are in thermal equilibrium even at 15 K. A fit of the model to the observed spin polarization lifetimes yields an energy gap of 47 cm-1 between the trip-quartet and trip-doublet. It is shown that the spin polarization evolves from a multiplet pattern at early times to a net absorptive pattern at late times following the laser flash. It is proposed that the establishment of thermal equilibrium leads to the evolution of the spin from multiplet to net polarization.
Metalloporphyrin π-cation radicals. Molecular structure and spin coupling in a vanadyl octaethylporphyrinate derivative. An unexpected spin coupling path
Schulz, Charles E.,Song, Hungsun,Lee, Young Ja,Mondal, Jalal U.,Mohanrao,Reed, Christopher A.,Walker, F. Ann,Scheidt, W. Robert
, p. 7196 - 7203 (2007/10/02)
The preparation and characterization of a π-cation radical derivative of a vanadyl porphyrinate is described. [VO(OH2)(OEP?)]SbCl6 is prepared by chemical oxidation of [VO(OEP)]; the formulation has been confirmed by a single-crystal X-ray structure determination. The coordinated water molecule of the unusual six-coordinate vanadyl complex is derived from solvent. Axial bond distances are the following: V-O = 1.578(4) A? and V-O(H2O) = 2.473(8) A?; the vanadyl ion is displaced 0.46 A? from the 24-atom mean plane. The average V-Np distance is 2.063 A?. Crystal data: a = 15.530(2) A?, b = 14.586(4) A?, c = 18.965(3) A?, and β = 106.20(1)°, monoclinic, space group P21/n, V = 4125.4 A?3, Z = 4, [VO2N4C36H45]SbCl6, R1 = 0.053 and R2 = 0.064 for 4707 observed data. EPR spectra have been measured for [VO(OH2)(OEP?)]SbCl6 in the solid (powder) state, in a single crystal, and in fluid and frozen solution. The solution-state EPR spectra of [VO(OH2)(OEP?)]SbCl6 are quite distinct, with vanadium hyperfine lines and with differing spectra in fluid and frozen solution. These solution spectra are identical to those reported earlier by others. In the solid state, the EPR spectrum of a polycrystalline sample consists of a single broad line with g = 1.99; single-crystal spectra also show vanadium hyperfine-splitting consistent with V-V coupling. The solid-state EPR intensity increases with increasing temperature. [VO(OH2)(OEP?)]SbCl6 has also been characterized by a detailed temperature-dependent (6-300 K) magnetic susceptibility study. Satisfactory fits of the temperature-dependent moments are obtained from a model in which the vanadyl electron is ferromagnetically coupled to the porphyrin cation electron (Jv-r = 63 cm-1) and two radical spins are antiferromagnetically coupled (Jr-r = -139 cm-1). This model also gives a satisfactory prediction of all solid-state EPR properties. The intramolecular ferromagnetic coupling is consistent with the principle of cospatial, orthogonal magnetic orbitals. The intermolecular antiferromagnetic coupling appears to arise from a novel, steplike orientation of pairs of (OEP*) radicals.
Vanadium(II) Porphyrin Complexes: Synthesis and Characterization. Crystal Structure of 2,3,7,8,12,13,17,18-Octaethylporphinatobis(dimethylphenylphosphine)vanadium(II)
Poncet, Jean-Luc,Barbe, Jean-Michel,Guilard, Roger,Oumous, Hassan,Lecomte, Claude,Protas, Jean
, p. 1421 - 1422 (2007/10/02)
The vanadium(II) porphyrins VII(PPhMe2)2(porp) containing phosphine ligands have been prepared from VIV(X2)(porp) porp = octaethylporphinato(oep), meso-tetraphenylporphinato, meso-tetra-m-tolylporphinato, meso-tetra-p-tolylporphinat
