published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

This dissertation focuses on structural and electrical characterization of self-organizing discotic molecular materials, specifically alkoxy and thioether side chain modified copper phthalocyanines, both in bulk and at organic/dielectric and organic /metal interfaces. A great deal of effort has been focused on understanding the self-organizing nature in these materials since molecular ordering is believed to control the intrinsic physical as well as electrical properties of these molecular aggregates. It was determined that side chains in these Pcs have a significant impact on the general ordering in these materials: alkoxy side chain modification favors a columnar hexagonal phase with a cofacial intracolumn alignment; thioether side chain modification, however, favors a tilted intracolumn alignment and much rigid columnar packing, driven by sulfur-sulfur interactions among adjacent molecular disks. Incorporation of styrene functionality in the side chain has been shown to enable photopolymerization. An optimal hexagonal columnar packing has been proved to be stabilized via photolysis at the mesophase. It is critical to explore the molecular ordering as well as the charge transport characteristics at interfaces since the organic/dielectric interface controls the charge accumulation in organic field-effect transistors (OFETs) and the metal/organic interface determines the charge injection in devices such as organic photovoltaic cells (OPVs). Two analytical tools have been developed in this dissertation work that successfully address these interfacial issues from a molecular level. 1) Probing interfacial structures at the organic/dielectric interface with X-ray reflectometry (XRR). Surface chemistry has shown a drastic impact on the ordering of the initially deposited materials. Surface engineering strategies, i.e. chemical modification, have been shown to significantly improve the coherence of molecular assemblies thereby optimizing charge transport properties of these molecular materials in an OFET platform. 2) Exploring charge injection and transport characteristics at molecular junctions with conductive-probe AFM (C-AFM). Charge injection processes at the metal/organic molecular junction have shown a strong dependence on the microstructure of these molecular materials. Thermionic emission and field emission were shown to be competing processes at these junctions. One dimensional charge transport is realized only with the appropriate molecular ordering in these discotic materials at metal/organic junctions. 3) Exploring structural and electrical properties of ITO with C-AFM. The ITO surfaces have shown both structural and electrical heterogeneity at the nanometer scale. A tunneling model has been proposed and the presence of thin insulating layers was believed to be the cause of electrically inactive regions of ITO. Aggressive chemical etching protocols have been developed and shown to improve the percentage of surface electrically active area, thereby, enhancing the electrode performance.

Thesis (M.Sc.)--York University, 2006. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 89-97). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR19645

Thesis (M. Sc.)--York University, 2002. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 105-110). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ82901.

Thesis (Ph.D.)--Bowling Green State University, 2006. / Document formatted into pages; contains xxi, 215 p. : ill. Includes bibliographical references.

Thesis (Ph.D. (Chemistry)) - Rhodes University, 2007.

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This work presents the synthesis, characterization, photophysicochemical and photoelectrochemical properties of anionic octa-caboxylated (MOCPcs), tetra-sulfonated (MTSPcs) and quaternized cationic (Q(T-2-Py)MPcs) water soluble aluminium, gallium, silicon, titanium and zinc phthalocynines. The peripherally tetra-substituted cationic (Q(T-2-Py)MPcs) and anionic (MTSPcs) were found to be aggregated in aqueous media, yet the octa-carboxylated (MOCPcs) counterparts were monomeric in solution. Cremophor EL (CEL) was used as a disaggregating agent, all the aggregated complexes disaggregated partially or completely in the presence of CEL. The photophysicochemical properties of aggregated complexes were investigated both in the presence of CEL and in aqueous media of pH 11 alone. Low triplet, singlet oxygen and fluorescence quantum yield were obtained in aqueous media (especially for the aggregated complexes) but a high improvement was achieved upon addition of CEL. The gallium complexes ((OH)GaOCPc and (OH)GaTSPc) showed good photophysicochemical properties with higher triplet and singlet oxygen quantum yields. For photoelectrochemistry the (MPcs) dyes were adsorbed to nanoporous ZnO, electrodeposited in the presence of eosin Y as structure directing agent (SDA) on FTO substrates by refluxing or soaking the films in a solution containing the dye of interest such that a full surface coverage was achieved. Quaternized cationic (Q(T-2-Py)MPc) and tetrasulfonated (MTSPcs) phthalocyanines formed strong aggregates when deposited on the surface of FTO/ZnO substrate leading. High external (IPCE) and internal (APCE) quantum efficiencies of up to 50.6% and 96.7% were achieved for the OTiOCPc complex. There was a lower overall cell efficiency for quaternized and tetrasulfonated metallophthalocyanines because of the strong aggregates when they were on the surface of the electrodes. Among the studied materials, OTiOCPc gave the highest overall cell efficiency of phthalocyanine electrodeposited on ZnO of so far  = 0.48%.

The syntheses, spectroscopic characterisation, photophysical and photochemical studies have been conducted for a variety of phenylthio substituted phthalocyanines (Pcs). Comparisons have been made taking into consideration the influence of the central metal ion, solvent properties and substituent type. The optical limiting properties were also determined for all the Pcs synthesised. A low-symmetry metallophthalocyanine complex was similarly characterised and the photoelectrochemical parameters determined when used as a sensitiser of nanoporous ZnO. The symmetric analogue was conjugated to gold nanoparticles to determine the influence of interactions on its photophysical properties and distinct differences occurred in the absorption and fluorescence spectra suggesting successful formation of conjugates.

The syntheses, extensive spectroscopic characterization, photophysical and photochemical studies have been conducted for a variation of d10 metallophthaloycanines (MPcs). Comparisons have been made taking into consideration the nfluence of the central metal ion, solvent properties, substituent type and position. Coordination to heavy central metals i.e. Hg gives enhanced triplet state properties. Low symmetry metallophthalocyanine complexes were similarly haracterized and the influence of nteractions with nanoparticles on their photophysical and photochemical properties determined. The MPcs have been linked and adsorbed or mixed with nanoparticles i.e. hemically functionalized single-walled carbon nanotubes SWCNT) and mercaptocarboxylic acid capped CdTe quantum dots (QDs) and changes in the spectra accounted for with respect to the proposed conjugate structures. Distinct differences ccur for linked and adsorbed or mixed conjugates in the bsorption, infrared (IR) and Raman spectra and for thermal ravimetric decay profiles, suggesting successful formation f covalent bonds (linked) and point to structurally ifferent materials. SWCNT quench MPc fluorescence by a photoinduced electron transfer mediated process to give low fluorescence quantum yields. The QDs were used as energy transfer donors and facilitate energy transfer, through Förster resonance energy transfer (FRET) from the QDs to the MPcs. Improved FRET efficiencies were found for linked MPc-QD conjugates relative to the mixed species. Photophysicochemical properties of MPcs were, in general, improved as a result of interactions with nanoparticles.