Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 191-203).

1,2,4,6-thiatriazine radicals can be neutral radical conductors in the context of molecular metal design. After initial investigations they were ignored in favor of other prospective ring systems. A more general route to 1,2,6-thiatriazine radicals herein is reported. Two crystal structures were obtained for the radicals 5-phenyl-3-trichloromethyl-1,2,4,6-thiatriazine 7c and 5-phenyl-3-trifluoromethyl-1,2,4,6-thiatriazine 8c. 7c displays a unique head-to-tail packing arrangement not seen in previous thiatriazine structures. Two crystal structures of the precursor phenyl/trichloro imidoylamidine 1c and phenyl/trifluoromethyl imidoylamidine 2c show strong intramolecular hydrogen bonding and relatively weak intermolecular hydrogen bonding. EPR of the radicals are highly diagnostic and display coupling to three unique nitrogen atoms, of which a small but very distinct influence on the hyperfine coupling constants from the remote aryl-substituents is seen. Solution electrochemistry assessed the redox tunability of the radicals to these substituents. DFT calculations of the hyperfine coupling constants and oxidation and reduction potentials corroborated well with experimental data. / xv, 176 leaves : ill. ; 28 cm.

-4Scm-1 whereas the hexamethyl was insulating. This was proposed to be due to differing stacking characteristics. The properties of the ternary salts were proved to be intrinsic and not solvent induced. The failure of the amphiphilic dipyrrylmethene to complex with TCNQ was proposed to be due to steric hindorance which encumbers the close approach of the TCNQ. The Langmuir film of the dipyrrylmethene was shown to undergo re-orientation on the subphase. The L-B film of a picolinium TCNQ charge transfer salt was shown not to under go a molecular re-orientation due to the increase in the area of the hydrophobic aliphatic chains.

The reflectivity of large single crystals of protonated and deuterated (TMTSF)₂Re0₄ and (TMTSF)₂BF₄ has been measured from ≈ 30 cm-¹ to ≈ 8000 cm-¹ using a Bruker IFS 113V Fourier Transform Interferometer for E / a and E / b' above and below the metal--insulator transitions at 177 K and 39 K respectively. The infrared powder absorption spectra of protonated and deuterated (TMTSF)₂Re0₄ has been measured from 200 cm˗¹ to 2000 cm˗¹. The Kramers-Kronig optical conductivity has been calculated from the reflectivity using Drude extrapolations to high frequency. The results for the conductivity for E / a show a one-dimensional density of states, characteristic of a one-dimensional semiconductor with strong electron-phonon coupling, with the vibrations appearing as resonances below the gap and as antiresonances above. The E / b' conductivity is smaller by almost two orders of magnitude than that for E / a, but displays the same semiconducting behavior. The phonons active in the E / b' polarization appear only as resonances. A normal coordinate analysis has been performed for protonated and deuterated TMTSF⁰ and TMTSF⁺. The results have been used to infer the frequencies of vibration and the deuterium shifts of TMTSF⁺⁰ׄ⁵. The molecular frequencies of vibration have been assigned on the basis of their observed frequencies and optical polarization, as well as their deuterium shifts. Some external phonons have also been assigned. The observation that many of the internal and external vibrations are split is due to the eightfold increase in the size of the unit cell (and subsequent reduction of the Brillouin zone) below the metal-insulator transition. The optical properties of the semiconducting state have been modelled for a one--dimensional molecular conductor with a twofold-commensurate charge-density wave, which accurately reproduces the effects of the lattice dimerization and the potential due to the anion chains. The calculations yield the electron-molecular-vibrational coupling constants for the totally symmetric a[formula omitted] vibrations of the TMTSF molecule. The model also yields a transfer integral of 1400 cm-¹ for both materials and semiconducting energy gaps of 2Δ = 1700 cm˗¹ and 2Δ = 1120 cm˗¹ for (TMTSF)₂ReO₄ and (TMTSF)₂BF₄ respectively. The optical conductivity in the E / b' polarization has been discussed in -terms of a two-dimensional band structure with anisotropic transfer integrals. The band structure calculations show the same general features as the measured spectra. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

published_or_final_version / abstract / Physics / Master / Master of Philosophy

Monomers and polymers containing the quinodimethane unit were synthesized. The infrared, nuclear magnetic resonance (NMR) and ultraviolet spectra of these materials were also reported. Oxidation of the enolate dianoion of α, α'-di(carbomethoxy)-α, α'-diphenylquinodimethane (DMPQH₂) with iodine gave 7,8-di(carbomethoxy)-7,8-diphenylguinodimethane (DMPQ) in greater than 50% yield. This compound had a reduction potential of -0.85V (Ag/AgCl reference) but would not form charge transfer complexes with electron donors. Attempted polymerization reactions of DMPQ were also discussed. A series of donor - acceptor substituted quinodimethanes was synthesized and a discussion of their electronic properties was included. Condensation copolyesterification of two of these materials was performed. Polymers with inherent viscosities ranging from 0.11 dL/g to 0.45 dL/g were obtained. The polymers were soluble at room temperature in hexafluoroisopropanol (HFIP) and a 1 : 1 solution of phenol/chlorobenzene. The polymers were also soluble at elevated temperatures in dipolar aprotic solvents.

In the past three decades, quasi-low-dimensional organic materials have attracted intense interests, both experimentally and theoretically. Due to their reduced dimensionality and relatively low carrier concentration, many organic materials exhibit strong electron correlations and numerous instabilities of the normal metallic state. The energy scales of such instabilities are often so low that the ground states can be changed by applying a reasonably strong magnetic field. Therefore, magnetic field is an effective tool for the study of quasi-low-dimensional organic materials. In this thesis, we will investigate two of these magnetic field related phenomena. In the first part, we will present our unified theory of angular magnetoresistance oscillations observed in organic conductors. We will demonstrate that, in spite of the absence of Landau level quantization for open Fermi surfaces in a magnetic field, a new quantum effect - Bragg reflections of electrons moving in the extended Brillouin zone - determines unusual magnetic properties of these materials. We will demonstrate that, at commensurate directions of a magnetic field, the electron motion shows 1D→2D dimensional crossover and leads to strong resistivity minima. We will present an analytic expression for interlayer resistivity, by both linear response formalism and solving the Boltzmann kinetic equation in the extended Brillouin zone. In two limiting cases, our general solution reduces to the results previously obtained for the LMA effects and LNL oscillations. We demonstrate that our theoretical results are in good qualitative and quantitative agreement with the existing measurements of resistivity in (TMTSF)₂ClO₄ conductor. In the second part, we will develop a theory for the recently observed high magnetic field high resistance state in (Per)₂Pt(mnt)₂. We demonstrate that the Pauli spinsplitting effects in a magnetic field improve nesting properties of a realistic quasi-onedimensional electron spectrum. As a result, a high resistance Peierls charge-density wave (CDW) phase is stabilized in high enough magnetic fields in (Per)₂Pt(mnt)₂ conductor. We show that, in low and very high magnetic fields, the Pauli spin-splitting effects lead to a stabilization of a soliton wall superlattice (SWS) CDW phase, which is characterized by periodically arranged soliton and anti-soliton walls. We suggest experimental studies of the predicted first order phase transitions between the Peierls and SWS phases to discover a unique SWS phase. It is important that, in the absence of a magnetic field and in a limit of very high magnetic fields, the suggested model is equivalent to the exactly solvable model of Brazovskii, Dzyaloshinskii, and Kirova.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Work on modelling compounds possessing die tetraaza[14]annulene (TAA) fragment is described. Modelling studies have been conducted to investigate both structural and electronic properties, of both single molecules and extended arrays of these compounds. The structural aspects have been investigated using molecular mechanics and crystallographic database investigations. Molecules based on the tetraaza[14] annulene structure have been found to adopt one of four conformations. The geometries of these conformations are planar, saddle-shaped, slightly twisted, and dome-shaped. The complexed metal centre and the arrangement of substituents on the periphery of the ligand, have been found to determine which conformation a molecule adopts. In order to model the compounds, three new atom types have been created for the Universal Force Field. The electronic aspects have been investigated using Hartree Fock based calculations for single molecules and Extended Huckel based calculations for extended systems. The electronics of die single molecules have shown there to be a linear trend in the LUMO energies, although die HOMO energies vary very little. The reason for this trend in the LUMOs is unknown, but appears not to be related to any obvious structural feature.