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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Semiquinone-Bridged bis-Dithiazolyls as Neutral Radical Conductors

Yu, Xin January 2011 (has links)
Radicals are potential building blocks to prepare conductive and magnetic materials. In order to achieve high conductivity, materials displaying a large bandwidth W and a low on-site Coulomb repulsion energy U must be generated. Semiquinone-bridged bis-1,2,3-dithiazolyl radicals (R = Cl, Ph, Me and the MeCN adduct of R = Cl) represent a new family of resonance stabilized neutral radical for use in the design of single-component conductive materials were prepared and fully characterized. In solid state these radicals remain as unassociated (monomers) in the solid state and typically form superimposed alternating π-stacks or slipped π-stacks, arranged in several different space groups. The predominate intermolecular interactions are S•••N′ and / or S•••O′ contacts, which increase the dimensionality from one dimensional π-stacked systems (i.e., poor lateral overlap) to two dimensional systems in the solid state. Thus the semiquinone-bridged bis-dithiazolyl radicals exhibit a significant decrease in activation energy (ca. 0.1 – 0.2 eV) and the conductivity is two to three orders of magnitude (ca. σ ≈ 1E-5 – 1E-2 S / cm) higher in comparison to the previously reported pyridine based systems. This high conductivity is attributed to the low on-site Coulomb repulsion energies (U) which were estimated from the solution cell potentials (EPC) obtained from CV measurements and improved bandwidth (W) from the S•••N′ and / or S•••O′ interactions. Furthermore, the all sulphur containing semiquinone-bridged bis-dithiazolyls have the lowest activation energies and the highest conductivity under ambient conditions compared with other all sulfur nitrogen based radicals known to date. The semiquinone-bridged bis-dithiazolyl (R = Cl) orderes as spin-canted antiferromagnets, TN = 8 K, and displayed large coercivity (80 Oe). The ZFC-FC measurement at low field (i.e., H = 100 Oe) established the phase transition temperatures and the spontaneous magnetization was used to estimate the spin canting angles (~ 0.14°). In the case of R = Ph, the antiparallel alignment of the ferromagnetic coupled chains leads to a spin-canted antiferromagnet (TN = 4.5 K), which undergo a unique field induced spin flop transition. The MeCN solvated of R = Cl behaves as a simple paramagnet at room temperature with bulk antiferromagnetic interactions, but no observed magnetic ordering from 2-300 K.
2

Semiquinone-Bridged bis-Dithiazolyls as Neutral Radical Conductors

Yu, Xin January 2011 (has links)
Radicals are potential building blocks to prepare conductive and magnetic materials. In order to achieve high conductivity, materials displaying a large bandwidth W and a low on-site Coulomb repulsion energy U must be generated. Semiquinone-bridged bis-1,2,3-dithiazolyl radicals (R = Cl, Ph, Me and the MeCN adduct of R = Cl) represent a new family of resonance stabilized neutral radical for use in the design of single-component conductive materials were prepared and fully characterized. In solid state these radicals remain as unassociated (monomers) in the solid state and typically form superimposed alternating π-stacks or slipped π-stacks, arranged in several different space groups. The predominate intermolecular interactions are S•••N′ and / or S•••O′ contacts, which increase the dimensionality from one dimensional π-stacked systems (i.e., poor lateral overlap) to two dimensional systems in the solid state. Thus the semiquinone-bridged bis-dithiazolyl radicals exhibit a significant decrease in activation energy (ca. 0.1 – 0.2 eV) and the conductivity is two to three orders of magnitude (ca. σ ≈ 1E-5 – 1E-2 S / cm) higher in comparison to the previously reported pyridine based systems. This high conductivity is attributed to the low on-site Coulomb repulsion energies (U) which were estimated from the solution cell potentials (EPC) obtained from CV measurements and improved bandwidth (W) from the S•••N′ and / or S•••O′ interactions. Furthermore, the all sulphur containing semiquinone-bridged bis-dithiazolyls have the lowest activation energies and the highest conductivity under ambient conditions compared with other all sulfur nitrogen based radicals known to date. The semiquinone-bridged bis-dithiazolyl (R = Cl) orderes as spin-canted antiferromagnets, TN = 8 K, and displayed large coercivity (80 Oe). The ZFC-FC measurement at low field (i.e., H = 100 Oe) established the phase transition temperatures and the spontaneous magnetization was used to estimate the spin canting angles (~ 0.14°). In the case of R = Ph, the antiparallel alignment of the ferromagnetic coupled chains leads to a spin-canted antiferromagnet (TN = 4.5 K), which undergo a unique field induced spin flop transition. The MeCN solvated of R = Cl behaves as a simple paramagnet at room temperature with bulk antiferromagnetic interactions, but no observed magnetic ordering from 2-300 K.

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