1,721,088 research outputs found
Simulation of EPR and Time Resolved EPR lineshapes in partially ordered phases
No full textSimulation of magnetic resonance spectra of probes in partially ordered glasses requires in principle a numerical integration on the full set of three Euler angles Ohm=(alpha beta gamma) from a laboratory fixed to a molecule fixed reference frame. It is shown that it is possible to manage efficiently this problem by using the algebraic properties of the Wigner matrix elements. This analysis is applied to time resolved EPR (TREPR) spectra of a series of bis-adducts of C-60 in the ordered glass of a nematic liquid crystal solvent. A paramagnetic triplet state is created by light excitation and TREPR spectra are obtained with the external magnetic field set parallel or perpendicular to the director n of the mesophase. The preferred orientation in the mesophase of the triplet state zero field tensor is determined
EPR study of in-plane anisotropy in the LB films of substituted phthalocyanines deposited on mylar sheets
No full textDetermination of proton hyperfine tensors of nitroxides by simulation of frozen ENDOR spectra.
No full textThe use of ENDOR spectroscopy of radicals in frozen solution is discussed. It is shown that by this technique it is possible to obtain the principal values of the anisotropic interactions of nitroxides and some information on their cosine directors
An electron nuclear double resonance study in a glassy matrix of nitroxide radicals with delocalized spin density.
No full textIndolinone (1), benzimidazole (2) and quinoline (3) nitroxide radicals have the nitroxide function in a conjugated position with respect to the π system. Their electron nuclear double resonance (ENDOR) spectra in a [2H8] toluene glassy matrix have been detected and the principal values and the orientation of the proton hyperfine coupling tensors have been obtained by comparison with computer-simulated spectra. Typical features of ENDOR spectroscopy in frozen solution, and in particular its more general feasibility with respect to use in solution, are discussed
Guest-guest interactions in urea inclusion compounds
No full textDifferent types of urea inclusion compounds have been studied to test the importance of the molecular interactions between guests in urea inclusion compounds. Experimental evidence has been obtained by the EPR spectra of guest radicals obtained by room temperature g ray irradiation of the inclusion compounds. The guest-guest intra-channel interactions are very important in the case of tridecandioic and tetradecandioic dicarboxylic acids guests which give rise to strong inter-molecular hydrogen bonding between the carboxylic groups. It is found that the molecular conformation of the tetradecanoic acid is strongly distorted to fit to the host channel dimensions. The interactions between guest molecules included in adjacent host channels have been modulated by varying the relative guest composition in a mixed 10-nonadecanone/nonadecane inclusion compound. It is shown that the molecular reorientation of the 10-nonadecanone guest becomes faster by increasing the nonadecane percentage as a consequence of the reduced inter-channel interactions
Intermolecular electron transfer in merocyanine aggregates studied by optical and transient EPR methods
No full textExcited states of two merocyanine chromophores have been studied by means of optical and magnetic resonance techniques. The dye molecules were dissolved in solvents of different polarity and cast in thin films on quartz surfaces. The optical absorption and emission spectra of both molecules indicate a little charge-transfer character in the S-0-S-1 transition. The cast films contain monomers and H type aggregates. EPR spectra have been obtained by time resolved techniques at low temperature after illumination of the sample. EPR spectra of isolated molecules in frozen solutions are typical of triplet excited states generated by spin-orbit promoted intersystem crossing. Two signals are observed in EPR spectra of the cast films, with a narrow line in emission superimposed on a very weak molecular triplet lineshape. The polarization and lineshape analysis suggest that a radical ion pair with a lifetime of the order of microseconds is formed by intermolecular charge migration following the photoinduced electron-transfer reaction between the donor and acceptor moieties of the chromophore
EPR study of in-plane anisotropy in the LB films of a Cu(II)[tetraalkoxycarbonyl] phthalocyanine deposited on mylar sheets
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