The magnetization generated by the interaction of stable radicals with photoexcited triplets in a viscous solution at room temperature was measured by light-induced Fourier transform electron paramagnetic resonance spectroscopy (FT-EPR). High and long-lived polarized magnetization (>100 µs in emission) is generated in the stable radical (R,γ-bisdiphenylene-β-phenylallyl) interacting with the photoexcited triplet state of free base, and Zn, tetraphenylporphyrin. Radical-triplet interaction was analyzed quantitatively employing a combined model of electron spin polarization transfer (ESPT) and radical-triplet pair mechanism (RTPM). The presented model allows calculating the radical polarization following an encounter with a thermal or nonthermal triplets. Moreover, an important conclusion from this study is that the generation of radical polarization via RTPM does not require efficient quenching of the photoexcited triplet.
The self-contained intravascular MRI catheter successfully identified TCFA and may prove to be an important diagnostic approach to determining the presence of lesions with increased risk of causing death or myocardial infarction.
A three-dimensional (3D) electron spin resonance (ESR) microimaging system, operating in pulse mode at 9GHz is presented. This microscope enables the acquisition of spatially resolved magnetic resonance signals of free-radicals in solid or liquid samples with a resolution of up to ∼3.5×7×11.4μm in 20min of acquisition. The detection sensitivity at room temperature is ∼1.2×109spins∕√Hz, which enables the measurement of ∼2×107 spins in each voxel after 60min of acquisition. The resolution and detection sensitivity are the best obtained so far for ESR at ambient conditions of temperature and pressure. This ESR microscope can be employed in the investigation of a variety of samples in the fields of botany, life sciences, and materials science.
Time-resolved EPR spectra of the lowest excited triplet state of boron subphthalocyanine chloride have been
measured in toluene at various temperatures (5−360 K). On the basis of the observed and simulated spectra,
electronic structure and molecular motion of the triplet state (1T) were analyzed, both in solid and fluid
solution. The simulations were carried out using a model, which considers a temperature-dependent exchange
between sites having different zero-field splitting (ZFS) parameters and molecular orientations. The ZFS
parameter, D, was nearly the same at all temperatures examined. At very low temperatures, below 20 K, the
spectrum was analyzed by a static model. At 40−120 K, two conformers with different ZFS parameter, E,
have been found. The population ratio between the two conformers showed strong temperature dependence.
These conformers were attributed to Jahn−Teller states and were identified by their different ZFS parameters.
The exchange rate and activation energy of the conformers were compared with similar experiments performed
in solid solution. Further increase in temperature (130−160 K) resulted in noticeable change in the spectra.
However, at this temperature range the spectra could not be analyzed quantitatively because of the unstable
crystal structure of toluene (soft glass). Above 163 K, the solvent turns slowly into fluid and the spectra were
strongly dependent upon temperature. In this range of temperatures, molecular rotations occur, initially around
the out-of-plane z-axis, and, as temperature rises, also around the in-plane x- and y-axes. Anisotropic exchange
rates were obtained from the spectral simulation and were analyzed by a population exchange between the
Jahn−Teller states combined with anisotropic rotations. Anisotropic spin−lattice (T
1) and spin−spin (T
2)
relaxation times were also obtained and discussed. The rotations become isotropic above 263 K, where the
spectrum exhibits a single sharp Lorentzian line and is analyzed in terms of the dipolar spin interaction.
An FT-EPR (Fourier transform electron paramagnetic resonance) method for the direct measurement of the electron spin polarization generated in stable radicals through photoexcited triplet and radical interaction is presented. This method depends on the ability to calculate numerically the filling factor of the irradiated volume in the EPR cavity. By this experimental method the polarization at different times after the laser pulse can be determined. This enables us to differentiate between the different processes generating the polarization in the radical, which are the ESPT (electron spin polarization transfer), when the triplet meeting the radical is still polarized, and the RTPM (radical triplet pair mechanism), for thermal triplets. The different time evolutions of the two mechanisms allow the spin-lattice relaxation time (T 1 ) of the triplet in liquid solution to be determined. Experimental verifications were made with galvinoxyl-porphyrin systems in toluene at different temperatures.
Electron spin resonance microcopy (ESRM) is an imaging method aimed at the observation of paramagnetic species in small samples with micron-scale spatial resolution. At present, this technique is pursued mainly for biological applications at room temperature and in relatively low static magnetic fields. This work is focused on the use of ESRM for the measurement of solid samples. First, a brief comparison of various electron spin resonance (ESR) detection techniques is provided, with an emphasis on conventional "induction detection". Following that, some methodological details are provided along with experimental examples carried out at room temperature and in a static field of approximately 0.5 T. These examples show for the first time the imaging of solid samples measured by "induction detection" ESR with a resolution better than 1 mum. Based on these experimental examples and capabilities, an outlook for the future prospects of this methodology in terms of spin sensitivity and resolution is provided. It is estimated that single-spin sensitivity could be achieved for some samples at liquid-helium temperatures and static fields of approximately 2 T. Furthermore, under these conditions, spatial resolution could reach the nanometer scale. Finally, a description of possible applications of this new methodology is provided.
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