Search

Results of in situ electron spin resonance, optical absorption, and Fourier transform infrared spectroscopic studies during electrochemical doping and undoping processes of viologen functionalized poly (3-alkylthiophenes) are reported. Effects of the functional group on the electronic properties of the polythiophene backbone in its conducting state are observed resulting in localization of the charge carriers. Radicals on the viologen side group show hyperfine structured electron spin resonance signals indicating a rapid motional averaging of anisotropic electron-nuclear couplings. Experimental results are discussed by comparison with other substituted polythiophenes in terms of conformational effects of the acceptor group on the conducting polymer backbone. A structural model with counterion complexation between polythiophene backbone and the viologen functional unit is presented. [ABSTRACT FROM AUTHOR]

We have determined the electron spin diffusion constant in (dicyclopentaheptalene)2SbF6 by means of a magnetic field gradient electron spin resonance spin echo technique. Parallel to the chain axis we obtain a value of D||≊0.064 cm2 s-1. From the comparison of temperature dependent conductivity and susceptibility measurements it is concluded, that the charge carriers are localized in this compound. These localized charge carriers can be described as a system of 1d-Heisenberg spin chains. The measured D|| value therefore corresponds to an effective exchange coupling constant of J≊4.5 meV (J/kB≊51 K). [ABSTRACT FROM AUTHOR]

Electron spin echo envelope modulation (ESEEM) with two- or three-pulse echoes has been observed in the triplet state of acridine in fluorene host crystals. Fourier transformation of the modulation pattern yield the quadrupole and hyperfine spectra of 14N and 2D nuclei. The hyperfine tensor elements for 14N as well as for m, α, and β deuterons are determined, rendering a refined spin density map of the acridine triplet state. [ABSTRACT FROM AUTHOR]

Investigates novel model systems for photo-induced intramolecular electron-transfer processes in anthracene- or quinquethiophene-fullerene diads and triads. Occurrence of charge transfer after excitation; Detection of a free induction decay and a broad spin-echo spectrum in both diad and triads at low temperatures.

The electronic properties of thiophene oligomers (nT, n=2–8) have been investigated in the lowest excited triplet state. Theoretical calculations of the zero field splitting parameters and of the π-electron spin density have been performed and compared with previous experimental EPR results. The calculations are based on a simple π-electron (one-electron-per-site) model including electron–electron interaction at the extended Hubbard level. Optimized bond lengths result from making them self-consistent to the corresponding bond orders via Coulson’s relationship. The calculated D values decrease from D=0.0959 cm-1 for n=2 to D=0.0597 cm-1 for n=8, in agreement with EPR data. The measured as well as the calculated E values are rather small. Furthermore, we found that ZFS parameters are affected by the torsion angles between the thiophene rings. The chain length dependence of D can be rationalized comparing π-electron spin density calculations and computed bond length distortions. These clearly indicate that the triplet excitation reaches a finite extension over about four thiophene rings. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present the results of 13C nuclear magnetic resonance (NMR) measurements on potassium and rubidium doped Buckminster fullerene C60 at room temperature. By using high-resolution magic angle spinning NMR spectroscopy we were able to identify and characterize the different, thermodynamically stable phases. Based on an analysis of the different NMR spectra, we discuss the effects of the intercalation on the molecular dynamics as well as on the electronic properties in these compounds. [ABSTRACT FROM AUTHOR]

We report nuclear magnetic resonance (NMR) experiments on 131Xe (I=3/2) gas-phase atoms which exhibit nuclear quadrupole interaction with the surface of the sample cell. Nuclear quadrupole coupling constants and quadrupole relaxation rates are obtained from the time-domain signal of the freely precessing nuclear magnetization in weak magnetic fields. The nuclear spin species is polarized by spin-exchange collisions with optically pumped ground-state spins of Rb gas atoms. The Rb atoms also present in the sample are used as a magnetometer to probe the free-induction decay of the nuclear-spin ensemble. The temperature dependence of both the effective quadrupole splittings and the relaxation rates are explained by a model for the surface interactions of a Xe atom adsorbed on the glass surface. The desorption is thermally activated with an activation energy of EA=0.12 eV. The surface diffusion of an adsorbed atom is characterized by an activation energy ED for thermally activated hopping between neighboring surface sites. Both energies enter the spectral density function governing wall-induced nuclear quadrupole relaxation. Our experimental results lead to the conclusion that they are on the same order of magnitude. [ABSTRACT FROM AUTHOR]

In zero field NMR, the spectra are characterized purely by the quadrupolar or dipolar interactions, which are sensitive to molecular motion. An analytical theory is presented which describes the effect of two-site flips of a deuteron on its zero field NMR spectrum and demonstrates the potential of this novel technique in the investigation of molecular dynamics. [ABSTRACT FROM AUTHOR]