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Thesis (Ph. D.)--Indiana University, School of Public and Environmental Affairs, 2006. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0156. Adviser: Ronald A. Hites. "Title from dissertation home page (viewed Feb. 22, 2007)."

Thesis (Ph.D.)--Lehigh University, 2009. / Adviser: Tianbo Liu.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3481. Adviser: Richard I. Masel. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

This dissertation explores the characterization of new phthalocyanine materials, and the processability of these materials with regard to thin film structures envisioned for use in organic based electronic devices. Highly ordered, coherent molecular assemblies are formed by Cu centered benzyloxyethoxy-substituted phthalocyanines. The influence of molecular aggregate interactions with solid supports, based on phenyl-phenyl interactions, manifests itself in large changes in wettability, and also in molecular orientations within those molecular aggregates. Selective deposition of these Pc assemblies was achieved based on chemical interactions with a heterogeneous surface. A facile process of creating alternating hydrophobic/hydrophilic regions on a Au substrate surface through a combination of microcontact printing and electropolymerization techniques (μCP/EP) was demonstrated. Optimization of the hydrophobic channel bottom regions with a phenyl terminated dopant results in patterned phthalocyanine stripes up to 500 μm in length. The substitution of a Co metal center does not appreciably influence the properties of the benzyloxyethoxy-substituted phthalocyanine material, although the lone pair electron, in the d(z)² orbital perpendicular to the Pc macrocycle, appears to be responsible for differences in molecular orientation. The ability of the Co metal to coordinate ligands (i.e. O₂) is particularly evident in electrochemical data taken of this material. Two new photoreactive phthalocyanines, with styryl- and cinnamyl-terminations, result in the formation of new materials, whose preliminary characterization is presented. The photoexcited polymerization of the styryl-substituted material resulted in formation of a 1-dimensional rod-like polymer material, with a mean rod length of 72 nm. The conversion percentages for this material routinely reached 30%, and are expected to improve with purer monomeric materials. The photolysis of the cinnamyl-terminated material routinely reach 70% conversion, and resulted in an insoluble material, that allows for photopatterning. Conventional interdigitated microelectrode (IME) measurements made on these materials show conductivities as high as ca. 10⁻⁸Ω⁻¹·cm⁻¹, and mobility values as high as 10⁻³ cm²·V⁻¹s⁻¹. These charge carrier properties, combined with the selective deposition possibilities (i.e. using patterned substrates and/or photolysis techniques) make this class of materials desirable for further investigation and applications in organic based electronic devices.

Increasing the efficiency and durability of organic light-emitting diodes (OLEDs) has attracted attention recently due to their prospective wide-spread use as flat-panel displays. The performance and efficiency of OLEDs is understood to be critically dependent on the quality of the device heterojunctions, and on matching the ionization potentials (IP) and the electron affinities (EA) of the luminescent material (LM) with those of the hole (HTA) and electron (ETA) transport agents, respectively. The color and bandwidth of OLED emission color is thought to reflect the packing of the molecules in the luminescent layer. Finally, materials stability under OLED operating conditions is a significant concern. LM, HTA, and ETA thin films were grown in ultra-high vacuum using the molecular beam epitaxy technique. Thin film structure was determined in situ using reflection high energy electron diffraction (RHEED) and ex situ using UV-Vis spectroscopy. LM, HTA, and ETA occupied frontier orbitals (IP) were characterized by ultraviolet photoelectron spectroscopy (UPS), and their unoccupied frontier orbitals (EA) estimated from UV-Vis and fluorescence spectroscopies in combination with the UPS results. The stability of the molecules toward vacuum deposition was verified by compositional analysis of thin film X-ray photoelectron spectra. The stability of these materials toward redox processes was evaluated by cyclic voltammetry in nonaqueous media. Electrochemical data provide a more accurate estimation of the EA since the energetics for addition of an electron to a neutral molecule can be probed directly. The energetic barriers to charge injection into each layer of the device has been correlated to OLED turn-on voltage, indicating that these measurements may be used to screen potential combinations of materials for OLEDs. The chemical reversibility of LM voltammetry appears to limit the performance and lifetimes of solid-state OLEDs due to degradation of the organic layers. The role of oxygen as an electron trap in OLEDs has also been verified electrochemically. Finally, a more accurate determination of the offset of the occupied energy levels at the interface between two organic layers has been achieved via in situ monitoring of the UPS spectrum during heterojunction formation.

Solid phase extraction (SPE) has been developed as an alternative to liquid-liquid extraction (LLE) in the sample preparation process. The advantages of SPE over LLE are that it is a more useful, reliable tool for sample preparation, which offers greater selectivity. The selectivity of an SPE sorbent is vital for the isolation of analyte from a biological matrix containing a myriad of interferences. The use of conventional ion exchange SPE for such an extraction process might not be adequate due to the adverse effects of interfering ions. Metals immobilized on various modified silicas were investigated to determine if the addition of metals improved selectivity. The selectivity of these sorbents was studied by the extraction of analytes from high ionic strength matrices. Extraction selectivity was found to depend on different factors, including the type of bonded species, metal ions used and the analytes, counter ions, sample pH and elution solvent composition. Utilizing coordination complexation between analytes and immobilized metal ions, particularly when different phases are stacked, can increase selectivity for a particular analyte. Metals immobilized by ionic exchange sorbents were observed to retain analytes of tridentate chelation capability more than immobilized metals on bonded chelators. However, bonded chelators were observed to be advantageous because they more strongly retained metal ions, relative to ionic exchangers. The interactions of immobilized silver ions with unsaturated molecules utilizing SPE were investigated. Retention of silver ions was found dependent on the nature of bonded phase. The silver ions immobilized by coordination interactions showed weaker retention than silver immobilized by ionic interactions. Retention of alkenes by silver was found to have higher flow dependence, as compared to ionic exchange or ligand exchange processes. Retention of analytes was observed to depend on a variety of factors, including the type of bonded phase used for silver immobilization, the composition of the elution solvent, steric factors, the degree of unsaturation, the geometry and position of the double bonds of the analyte molecules. Extraction selectivity for geometrical isomers decreased when silver ions were immobilized by long chain cation exchangers versus those on conventional short chain cation exchangers.

To increase the applicability of spectroelectrochemistry to ultrathin films at a transparent semiconductor electrode, a single-mode, step-index electroactive integrated optical waveguide (the EA-IOW) incorporating an indium tin oxide top layer as an electrode was developed. The EA-IOW is much more sensitive to absorbance by molecular adlayer species than previous electroactive waveguide designs; a sensitivity increase of ca. 4000 relative to a single-pass transmission experiment has been measured by monitoring the reduction of a surface-adsorbed dye molecule. An important characteristic of the present three-layer EA-IOW structure is that its design is close to being optimized in terms of maximizing sensitivity while maintaining acceptable optical losses, as determined by theoretical modeling. Before the EA-IOW can be applied to measure absorbance changes arising from electron transfer in ultrathin films, the background optical changes that occur as a function of potential must be understood. There is a linear decrease in outcoupled intensity as the EA-IOW is scanned negative which is a result of an increase in the number of free carriers inside the ITO, a highly reproducible effect. There is also a poorly reproducible non-linear component to the optical background, accompanied by a hysteresis between the forward and reverse potential scans, that disappears after conditioning the EA-IOW in electrolyte solution for a period of several days. It is hypothesized that his effect is due to hydroxylation of the ITO network. To test the EA-IOW experimentally, the reduction of surface-adsorption methylene blue was monitored, along with the formation of Prussian blue during the electrochemistry of ferricyanide. Two experimental applications of the EA-IOW will be reviewed; first, the EA-IOW was used to measure the spectroelectrochemistry of submonolayer films of phthalocyanine polymeric assemblies to compare the electrochemistry at submonolayer and multilayer coverages. Finally, the use of the EA-IOW in protein electrochemistry will be discussed. The dichroic ratio of cytochrome c adsorbed to indium tin oxide was measured as a function of potential, and found to be consistent with an orientation of the heme ligand that is almost parallel to the electrode surface. Also, a change in heme orientation was detected during reduction of the protein.

Light generation in organic light emitting diodes (OLEDs) requires the recombination of electron-hole pairs at a p-n junction. Radiative recombination has been investigated with solution electrochemical studies of the principal lumophores, dopants, and hole-transport agents of small molecule OLEDs. We have found that solution electrogenerated chemiluminescent (ECL) reactions between radical anion and cation states of OLED components model the spectral output and efficiency of solid-state electroluminescence. These studies have shown that the molecular structures of commonly used materials in OLEDs are not optimized. ECL has been used to develop and optimize new materials that dramatically improve device performance. The results of the ECL experiments can be explained using commonly accepted electron transfer theories. Nonaqueous electrochemistry and spectroelectrochemistry have been used to study the energetics and stability of radical cation states of new and existing biphenyl-bis-triarylamines (TPDs), triphenylamines, and carbazoles, common hole-transport materials in OLEDs. We have established that these triarylamines, upon anodic oxidation, cation radicals with widely variable stability that react via coupling-deprotonation to form a neutral dimer. We have quantified the decay of these reactions by following the visible absorption decay of the cation radicals. The stability of these states to dimerization reactions is critically dependent on molecular structure. We speculate that these dimerization reactions could occur in the solid state, and that this reaction could lead to OLED degradation, since it involves the loss of a proton. Derivatives of 9,10-diphenylanthracene were synthesized for use as Forster energy transfer dopants and stable charge traps in OLEDs. Cyclic voltarnmetry shows that these compounds form stable radical cation and anion states in nonaqueous electrolytes. Introduction of substituents to the anthracene ring can modify the HOMO - LUMO gap of these structures. When these molecules are doped into poly(N-vinylcarbazole), they act as Foster energy acceptors. Photoluminescent and electroluminescent spectra of these doped polymer composite films show that the luminescence originates from the singlet excited state of the diphenylanthracenes. Preliminary results of single layer OLEDs made from these materials are promising; device external quantum efficiencies attained up to ca. 1.2 % and brightness up to 800 cd/m² at 12 volts.

The total entropy of melting for a wide variety of compounds is estimated by a modification of Walden's rule. This modification accounts for the effects of both molecular rotational symmetry and molecular flexibility on entropy. These effects are combined into a single simple semi-empirical equation. The intercept of the equation was modified from Walden's rule (56.5 J/K·mol), which uses a small data set, to 50 J/K·mol, which uses a data set of 237 rigid and asymmetrical molecules. The molecular rotational symmetry number, σ, and molecular flexibility number, φ, are separately defined and evaluated for a wide variety of molecules and are shown to be related to the entropy of melting in Chapters II and III, respectively. The two effects are combined so that a single equation can be used to predict the entropy of melting for any nonelectrolyte compound. This semi-empirical equation is tested on an independent data set. For over 930 different molecules, including those which are both rigid and flexible, the average absolute error between the predicted and observed entropy of melting values is only 12.5 J/deg·mol. This difference is within experimental error.