Search results for " paramagnetic resonance"
showing 10 items of 567 documents
Porphyrin amino acids-amide coupling, redox and photophysical properties of bis(porphyrin) amides.
2013
New trans-AB2C meso-substituted porphyrin amino acid esters with meso-substituents of tunable electron withdrawing power (B = mesityl, 4-C6H4F, 4-C6H4CF3, C6F5) were prepared as free amines 3a-3d, as N-acetylated derivatives Ac-3a-Ac-3d and corresponding zinc(II) complexes Zn-Ac-3a-Zn-Ac-3d. Several amide-linked bis(porphyrins) with a tunable electron density at each porphyrin site were obtained from the amino porphyrin precursors by condensation reactions (4a-4d) and mono- and bis(zinc(II)) complexes Zn(2)-4d and Zn(1)Zn(2)-4d were prepared. The electronic interaction between individual porphyrin units in bis(porphyrins) 4 is probed by electrochemical experiments (CV, EPR), electronic abso…
Greatly enhanced intermolecular π-dimer formation of a porphyrin trimer radical trications through multiple π bonds.
2010
A trefoil-like porphyrin trimer linked by triphenylamine (TPA-TPZn(3)) was synthesized. A three-electron oxidation of TPA-TPZn(3) forms a radical trication (TPA-TPZn(3)(3+)), in which each porphyrin ring undergoes a one-electron oxidation. The radical trication TPA-TPZn(3)(3+) spontaneously dimerizes to afford (TPA-TPZn(3))(2)(6+) in CH(2)Cl(2) . The characteristic charge-resonance band due to the charge delocalization over the π system of (TPA-TPZn(3))(2)(6+) was observed in the NIR region. The initial oxidation potential of TPA-TPZn(3) is negatively shifted relative to that of the corresponding monomer porphyrin, which results from the stabilization of the oxidized state of TPA-TPZn(3) as…
Radical cations of vitamin E
2002
Radical cations of vitamin E compounds (α-, β-, γ- and δ-tocopherols and α-, β-, γ- and δ-tocotrienols) were for the first time successfully prepared in different solvents. Their unpaired electron distribution was solved by means of EPR and ENDOR spectroscopy and assignment of isotropic hyperfine couplings was performed. The isotropic hyperfine coupling constants calculated theoretically (UB3LYP) were comparable to those studied experimentally. Radical cations were observed to exist as an intermediate product in the formation of the neutral radical. Moreover, loosening the proton from the radical cation of α-tocopherol and from α-tocotrienol produced the neutral radical, which was detected …
ESR, electrochemical and cyclodextrin-inclusion studies of triazolopyridyl pyridyl ketones and dipyridyl ketones derivatives.
2008
Abstract The electron spin resonance (ESR) spectra of free radicals obtained by electrolytic reduction of triazolopyridyl pyridyl ketones and dipyridyl ketones derivatives were measured in dimethylsulfoxide (DMSO). The hyperfine patterns indicate that the spin density delocalization is dependent of the rings presented in the molecule. The electrochemistry of these compounds was characterized using cyclic voltammetry, in DMSO as solvent. When one carbonyl is present in the molecule one step in the reduction mechanism was observed while two carbonyl are present two steps were detected. The first wave was assigned to the generation of the correspondent free radical species, and the second wave…
Quantitative evaluation of the preferential orientation ofpara-phenylene vinylene pentamers in polystyrene films by optically detected magnetic reson…
2007
The morphology of drop-casted and spin-coated films of blends ofpara-phenylene vinylenederived pentamers with polystyrene is investigated by means of X-band optically detected magnetic resonance (ODMR) of the triplet excited states. Adapting an electron spin resonance simulation program to ODMR, the orientation distribution function of the oligomers in the films could be quantified. After drop casting or spin coating the pentamers from a solution, the oligomers tend to lie with their backbones in the plane of the film. The parameters of film preparation and the type of pentamer strongly influence the orientation distribution function. Also, the study of preferentially oriented films allows …
Switching nuclearity and Co(II) content through stoichiometry adjustment: {Co(II)6Co(III)3} and {Co(II)Co4(III)} mixed valent complexes and a study o…
2015
We are reporting two new mixed valent Co(ii)/Co(iii) polynuclear complexes, {Co II 6 Co III 3 } and {Co II Co III 4 }, bearing different amount of Co(ii) ions in their cores, through the employment of the multidentate triethanolamine (teaH 3 ) ligand in different stoichiometric ratios. We present a complete picture of the magnetic behaviour of both complexes through a combined usage of the susceptibility, magnetization and X-band EPR data as well as broken-symmetry DFT calculations. Compound 1 shows an atypical spin-only behaviour, probably due to the presence of four and five coordinated Co(ii) sites as well as highly distorted six coordinated Co(ii) ions, promoting a high degree of orbita…
Electron paramagnetic resonance of doped and undoped BaFBr detected by recombination luminescence
1998
Abstract The recombination processes in the X-ray storage phosphor BaFBr:Eu2+ was investigated by measuring the microwave-induced changes in the recombination luminescence in a (high) magnetic field. Besides the resonances of the F(Br−) centre, of the VK(Br−2) centre and of the Eu2+ ground state we observed a line of a hitherto unknown hole centre. The maximum of the luminescence band in which the VK(Br−2) centre could be detected was about 400 nm. The resonance of the unknown hole centre belongs to a luminescence band peaking at about 350 nm.
Tl-related radiation defects in CsI:Tl
2004
Abstract Angular dependencies of the EPR spectra detected via the magnetic circular dichroism of the optical absorption (MCDA-EPR) observed in the MCDA bands at 355, 411, 425, 442, 465, 536, and 815 nm of γ- or X-irradiated CsI:Tl crystals have been investigated. The MCDA-EPR spectrum at B || [1 0 0] consists of two quartets of intense lines. The spectrum could be satisfactorily explained taking into account hyperfine (hf) interactions of unpaired electron with S= 1 2 with three Tl nuclei I ( 205 Tl , 203 Tl )= 1 2 . Therefore we propose as a model a Tl-trimer centre. The hf interactions along a [1 0 0] direction with two equivalent Tl and one single Tl were observed. As a centre model we p…
Self-trapped holes and recombination luminescence in LiBaF3 crystals
2001
Abstract We investigated electron paramagnetic resonance (EPR) angular dependencies, recombination afterglow and thermostimulated luminescence of undoped LiBaF3 crystals, X-irradiated at low temperatures. EPR parameters of the F2− molecule oriented along the [1 1 0] direction have been obtained. Based on the value of the g-shift Δg=g⊥−gII=0.02, characteristic for the VK-centres in similar perovskites, we propose that we indeed observed the VK-centres, not the H-centres. X-irradiation below 170 K results in creation of a long-time temperature-independent afterglow due to the tunnelling recombination between close electron and hole centres. The F-type electron centres and the VK as well as pr…
EPR of molybdenum-related defect in CdWO4 crystal
1998
Abstract EPR spectra of a molybdenum-related structure defect have been observed at a temperature of 20 K in CdWO 4 scintillator crystal, being as-grown “blue-coloured”. Mo 95 and Mo 97 isotope superhyperfine ( shf ) splittings have been resolved. Further splittings in EPR spectra have been interpreted as arising from shf interactions with W nuclea. In the present model of the defect, the unpaired spin is localised in the Cd-site position and molybdenum replaces one of the neighbouring W atoms.