15,307 research outputs found
Spectroscopic studies of (TCNQF4)3[N(CH3)4]2
No full textInfrared, Raman and EPR spectra are used to characterize the charge and spin distribution on the molecules of the title compound which was before found to have a ferromagnetic phase also at room temperature. We find that the charges and spins are localized on the tight dimers present in the crystal, a situation which is consistent with a local diamagnetic ground state which cannot determines a spin polarization of the system. We also studied some defects of the crystals which seem to generate in the crystallization. We produced
these defects by grinding the crystals and found that they have a spin and are likely to be charged. Preliminary magnetic measurements do not allow us, however, to conclude that such defects are involved in the ferromagnetic behavior of the compound
Experimental evaluation of the electron-intramolecular-vibration coupling constants of tetramethyltetrathiafulvalene
No full textThe relevant electron-intramolecular vibrations coupling constants of tetramethyltetrathiafulvalene (TMTTF) have been experimentally obtained. The determination was possible studying the optical properties of dimers of TMTTF(+) in polymethyl-methacrylate films on the basis of a Holstein-Hubbard dimer model. Electron paramagnetic resonance measurements of the singlet-triplet energy gap of the dimers made possible the calculation of the coupling constants without the need for absolute values of the optical spectra and the knowledge of structural parameters. The values of the coupling constants show differences with previously reported values for TMTTF or related molecules like TTF and bis-ethylenedithio-TTF (BEDT-TTF)
ENDOR SPECTRA OF 2-METHYL-NAPHTHALENE-TCNB TRIPLET TRAP IN NAPHTHALENE-TCNB SINGLE-CRYSTALS
No full textNaphthalene-TCNB charge transfer crystals doped with 2-methyl naphthalene illuminated by visible light give rise to triplet traps which have been identified by EPR and ENDOR spectroscopy as 2-methyl naphthalene-TCNB CT complexes in their first excited triplet state. The complete hyperfine tensors of all the 2-methyl naphthalene protons have been obtained by analysis of the variation of the ENDOR frequencies with the crystal orientation in the magnetic field. The structure of the CT complex, the spin distribution and the CT character are discussed
Paramagnetic C60 derivatives with one and more unpaired electrons: Spin polarization and photoelectron transfer
No full textFullerene C60 derivatives covalently linked to a nitroxide radical are studied by Time Resolved EPR. The interaction
between radical and triplet or singlet excitation,lo calized on the fullerene moiety,gives rise to spin polarization of the
radical EPR signal. The quartet state of the Radical Triplet Pair (RTP) is also observed by EPR. Electron transfer
involving the excited fullerene triplet is studied through the effects on the spin polarization pattern
Time resolved EPR of [70]fullerene monoadducts in the photoexcited triplet state
No full textTriplet excited states of isomers alpha, beta and gamma of N-methyl-[70]fulleropyrrolidine in glassy toluene (T = 120 K) are investigated with Time Resolved EPR (TR-EPR) spectroscopy using pulsed laser photoexcitation. Both the zero field splitting (ZFS) parameters D, E and the anisotropic triplet population rates are measured. Results reveal a strong dependence of the triplet state wavefunction on the position (alpha, beta or gamma) of the pyrrolidine addend with respect to the pole of the [70]fullerene unit. The relevant molecular orbitals have been calculated giving support to this finding. The dipolar tensor principal axes are located at the molecular reference frame from the inspection of the EPR spectra in a frozen liquid crystal (E7). Time evolution of the triplet EPR signals is different among the isomers, suggesting different triplet lifetimes and/or spin relaxation properties. The spin-density distribution in the first triplet state for N-methyl- [70]fulleropyrrolidine is compared with that previously observed for pristine C70
Electron spin polarization of doublet state species due to interaction with excited triplet states in single crystals
No full textDoublet states species trapped in crystalline solids show transient spin polarized EPR spectra if the crystal is illuminated by visible or UV light. The spin polarization is accounted for by the interaction of the doublet species with photoexcited triplet states. The mechanism of the process producing the spin polarization is examined and some experimental examples are discussed. The analysis of the time evolution of the transient variation of the EPR signal allows the measurements of the spin lattice relaxation time and in some cases of the diffusion rate of mobile triplet excitations in the crystal lattice
Photoswitching of triplet-triplet annihilation upconversion with photo-generated radical from hexaphenylbiimidazole
No full textPhotoirradiation generated radical from hexaphenyl-biimidazole (HPBI) was used for reversible
switching of triplet-triplet annihilation (TTA) upconversion, based on quenching of the photosensitizer
triplet state by radical-triplet pair mechanism. Upon 365 nm irradiation, the TTA upconversion in a
system composed by a boron-dipyrromethene (BODIPY) derivative and perylene, was completely swit-
ched off due to quenching of triplet state of photosensitizer by photogenerated radical from HPBI. The
upconversion was recovered after leaving the samples in darkness, due to regeneration of HPBI Dimer.
The photophysical process involved in the photochromism and photoswitching of TTA upconversion
were studied with steady-state UV–vis absorption spectroscopy, nanosecond transient absorption
spectroscopy and EPR spectroscopy
Precise determination of the orientation of the transition dipole moment in a Bodipy derivative by analysis of the magnetophotoselection effect
No full textMagnetophotoselection effects, observed for the lowest triplet state of a boron-dipyrromethene (Bodipy) derivative by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy, have been exploited to determine with a good precision of about 5° the 3D orientation of the singlet-singlet transition dipole moment (TDM) in the molecular frame. We have shown that the TR-EPR spectrum lineshape, obtained using a polarized laser pulse, is different from that obtained by using depolarized light. We first developed a new model for the simulation of the TR-EPR spectra obtained with polarized light excitation; the model explicitly takes into account the orientation of the TDM in the molecular frame. We then applied the method for the determination of the TDM orientation, directly from glassy frozen isotropic solutions of Bodipy. The experimentally determined direction has been compared with that obtained from quantum mechanical calculations
EPR study of in-plane anisotropy in the LB films of a Cu(II)[tetra alkoxy carbonyl] phthalocyanine deposited on mylar sheets
No full textElectron paramagnetic resonance spectroscopy has been applied to obtain information on the in-plane anisotropy of Cu(II) [tetrakis-(3,3-dimethyl-1-butoxy carbonyl)] phthalocyanine (CuPcBC) molecules deposited as a Langmuir-Blodgett film on a biaxially oriented mylar substrate. We have found that the in-plane distribution of orientations of the film molecules depends on the angle between the asis of preferential order identified in the substrate and the dipping direction. The in-plane orientational anisotropy of the material in the film is mainly due to the ability of the substrate to induce oriented growth of CuPcBC molecules which reflects its surface order
Declaration of Intention for Antonio Franchihtti
No full textDeclaration of Intention to become a citizen of the United States, as filled out and signed by Antonio Franchitti. Applicant lists himself as a 47 year old farmer residing in Hammonton, New Jersey, born in Campombosso, Italy on 18 April 1870, who sailed on the US bound vessel Britania. Declaration submitted and sworn April 21, 1917
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