Organic semiconductors hold the promise of electronic devices whose manufacturing scalability and form factor versatility could disrupt the existing electronics market. From a commercial feasibility standpoint, however, the technology is still in its relative infancy. To date, significant research effort has been directed toward developing polymers and small molecules for use in solution-processed thin-film bulk heterojunction organic photovoltaics (BHJ OPVs) and field-effect transistors (OFETs). A key goal of this research is to better understand the structure-property relationships that govern material performance. Molecular structure has been shown to influence material properties such as light absorption, intermolecular electronic compatibility, charge transport characteristics, thin-film morphology, and molecular packing. Similarly, processing steps such as the use of certain electronic interlayers or the incorporation of solvent additives can have a dramatic improvement on device performance.

In this work, polymer and small molecule systems are used to investigate such structure-property relationships, particularly ones governing solid-state nanostructure. Seemingly small changes in structure are shown to have a significant and systematic impact on OPV and OFET device performance. We investigate how a solution-processed organic semiconductor's π-conjugated backbone, end-capping groups, and solubilizing aliphatic side-chains can have a profound impact on nanostructure and device performance. In addition, we study how the processing conditions of polymers used in OPV and OFET devices affect solution-phase thermodynamics, as well as the dynamics of spin-coating and film formation. In both polymer and small molecule systems, we have demonstrated forward-looking design and processing principles that can inform the development of the next generation of ever higher-performing OPV and OFET materials.

The utilization of light to produce useful responses holds much potential for changing the world through smart materials and photovoltaic systems. We report the utilization of a variety of carbon nanotube composites as photovoltaic devices or as optothermal materials for the controlled placement of heat. Toward carbon nanotube - polymer photovoltaics we have successfully shown supramolecular compatibilization and functional bilayer devices. Opothermal processes are shown to manipulate a variety of system variables: surface energy, surface tension, and pressure. By manipulating these variables interesting responses are produced. Optothermal surface energy control produced wettability switches of 70º on composite surfaces. Optothermally modulated surface tensions of fluids converted light into work in the form of controlled linear motion, rotational motion, and volumetric expansion. Optothermally heated liquids confined within impermeable microcapsules resulted in the phototriggerable release of chemicals on demand. This release allowed small molecule reactions and polymerizations to be remotely initiated in a spatially selective manner. These results lay the framework for the expansion of the field of advanced optothermally responsive materials.

The goal of this research was to develop methods to control the material properties of organic semiconductors, like solubility, stability, charge mobility, and self-assembly, through structural design. Investigations of structure-property relationships were conducted to optimize the properties of organic semiconductors for applications in organic field effect transistors (OFETs) and organic photovoltaics (OPVs).

Chapter 1 gives an introduction to charge transport in organic semiconductors, and describes how the structure of conjugated molecules can affect their electrical performance and facilitate facile solution deposition. Furthermore, factors that can affect the stability of organic semiconductors to ambient conditions are discussed. Also, the device characteristics of OFETs and OPVs are summarized as a reference for subsequent chapters.

Chapter 2 discusses the investigation of the air stability of distyryl oligothiophenes in OFETs. This work made use of thermally labile solubilizing groups to facilitate solution deposition of the oligothiophenes. In addition to device characterization, an extensive analysis of the thin film morphology using AFM, NEXAFS and GIXD is presented. This work revealed the general stability of distyryl oligothiophenes to oxidative degradation, and the high degree of crystallinity in our thin films.

In Chapter 3, the charge transporting properties of pentathiophene monolayer islands is analyzed using current sensing AFM. The pentathiophenes were prepared with carboxylic acid moieties for self assembly, and the sub-monolayer films were transferred onto conductive substrates using the Langmuir-Blodgett technique. The morphology of the monolayers was observed to be sensitive to the alkyl substitution pattern of the pentathiophenes, which in turn affected charge transport.

Hierarchical supramolecular assemblies of oligothiophenes and block copolymers are studied in Chapter 4. The structure of the assemblies is studied by TEM and small angle X-ray scattering, confirming successful formation of supramolecular assemblies. Thin films are studied further by grazing incidence X-ray scattering, and their charge transporting properties are evaluated in OFETs. This work demonstrates that non-covalent self-assembly can be used to access nanostructured thin films of functional organic semiconductors.

Finally, Chapter 5 discusses the photophysical, morphological, and electronic properties of boron(subphthalocyanine)s with conjugated axial ligands. The tendency of these materials to form polycrystalline films instead of amorphous films was shown to be very sensitive to axial ligand structure and coordination geometry. The morphology of thin films was also shown to affect OPV device characteristics, with crystalline films supplying higher photocurrents.

Vaccination represents one of the most cost-effective methods for the treatment and prevention of disease. Due to safety concerns surrounding the use of live attenuated and killed/inactivated pathogens, there has been significant interest in the development of subunit vaccines, which are composed of discrete antigenic proteins or polysaccharides. Unfortunately, protein-based vaccines are poorly immunogenic and typically require the use of adjuvants for the induction of protective immunity. Because of their tunability and synthetic addressability, polymeric particulate carriers represent a promising approach for enhancing the efficacy of protein-based vaccines, and are the subject of this dissertation. In particular, we report on the development of acid-degradable materials, which are capable of releasing encapsulated protein antigens and immunostimulatory molecules following uptake by cells of the immune system and subsequent trafficking to acidic endosomal vesicles. Specific emphasis is placed on the development, functionalization and immunological evaluation of biodegradable acid-sensitive particle systems.

Chapter 1 introduces various delivery strategies for enhancing the potency of subunit vaccines and discusses the basics of vaccine immunology. Additionally, the field of polymeric particulate antigen carriers is reviewed, with a focus on relevant design criteria for materials intended to interact with the immune system.

In Chapter 2, the synthesis of acid-sensitive acrylamide-based microparticles containing an immunomodulatory agent is discussed. The optimal conjugation strategy for an immunostimulatory DNA sequence is investigated and particles containing a model protein antigen are studied in several models, including a cancer immunotherapy study, to ascertain in vivo the importance of co-delivering antigen and maturation signals to cells of the adaptive immune system.

Chapter 3 discusses the synthesis of a second generation acid-sensitive polyurethane particle system which is designed to degrade entirely into biocompatible small molecule byproducts. The ability of these particles to elicit an immune response to a model antigen is studied and a method to monitor the production of polymer degradation byproducts in cells is presented.

Chapters 4 and 5 investigate the synthesis, characterization, and a method for the functionalization of a third generation acid-sensitive particle system. The preparation of these particles from acetal-modified dextran and their pH-dependent degradation behavior is described. Additionally, a facile method for the surface functionalization of these particles using alkoxyamine reagents is presented.

Organic light emitting diodes (OLEDs) prepared from electroactive materials show great potential for multicolor display and white light source applications. Unfortunately, the commercialization of multilayer OLEDs has been slow. This can be attributed in part to the vapor deposition technique used to assemble small molecule thin films. The process is not amenable to large area displays and is relatively costly. An attractive alternative solution to this problem is to replace small molecules with organic polymers, which could be solution processed in an efficient and economical manner. Polymeric materials also offer the unique potential to achieve nanoscale self-assembled structures through their functional architecture. These materials can be solution processed and mimic multilayered small molecule devices to achieve improved performance and/or balanced color. Design and synthesis and OLED testing of functional polymers which can achieve defined multilayer or nanostructured film characteristics through simple solution processing is the focus of this thesis.

In Chapter 1, the history of OLED materials as well as the device mechanism and key organic electronic characteristics necessary for high performance devices is introduced. There is also a discussion on the methods for device testing and characterization.

The design and synthesis of novel dendronized linear polymer host materials is presented in Chapter 2. These polymers should possess a rigid linear rod like architecture which had not been investigated for its potential to order a thin film in an assembly of cylindrical structures. This host material was desired in order to optimize the interface of hole and electron transporting material to achieve improved recombination in the thin film.

Similarly, in Chapter 3 a diblock copolymer architecture is studied as host material in OLED devices. In this work the differences between nanoscale self assembled diblock copolymers of hole and electron transporting units and random copolymers of the same composition are studied. These materials show a high external quantum efficiency of 5.6 % for a simply prepared single layer device which is enabled by the self-assembly of the functional diblock copolymer architecture.

In Chapter 4, these diblock copolymers are exploited not only to create nanoscale domains of hole and electron transporting domains but also to organize the site isolation of two different colored phosphorescent emitters. Polymerizable heteroleptic iridium complexes of different color were developed and covalently incorporated into separate blocks of the diblock copolymer. Following the self assembly of thin film morphology through simple spin coating, the energy transfer from blue to red emitters was greatly reduced enabling synergistic dual emission for white electroluminescence.

Chapter 5 discusses the design and synthesis of electroactive crosslinked polymer nanoparticles with nanoscale size that can achieve the site isolation of emitters. Using different polymerizable iridium complexes, batches of different colored polymer nanoparticles can be simply prepared and mixed at the device preparation stage in any ratio to yield tunable colored devices. These nanoparticles dispersions behave as light emitting inks which can be simply solution processed with predictable and stable electroluminescent color.

In Chapter 6, difunctional polymerizable iridium complexes are used to achieve multilayer structures of electron blocking layers and phosphorescent emissive layers. These small molecules can be solution processed to yield thin films which can be crosslinked through simple heating step. A subsequent layer can then be deposited on top to build up all solution processed multilayered devices. A select high triplet energy crosslinkable iridium complex was shown to perform well as an electron blocker and hole transporting layer in OLEDs with improved performance over the standard water soluble hole transporting layer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).

RNA interference (RNAi) represents a promising method for the treatment and prevention of disease. Due to the tremendous potential of RNAi as a therapeutic strategy, there has been significant interest in the development of delivery vehicles which could efficiently deliver siRNA and reduce the expression of a protein of interest. Unfortunately, translation of the potential of siRNA into the clinic is limited by the lack of safe and effective delivery systems. Because of their tunability and synthetic addressability, acid–degradable polymeric materials represent a promising approach for the delivery of siRNA and are the subject of this dissertation.

Acid–sensitive systems have particularly desirable characteristics, as payload release can be triggered in response to endosomal acidification upon uptake. In particular, we describe the development, functionalization, and biological evaluation of biodegradable polymer systems which can efficiently deliver siRNA therapeutics to non–phagocytic cells. Specific emphasis is placed on the development of materials that have optimal physicochemical properties for pulmonary delivery.

Chapter 1 introduces various delivery strategies for siRNA therapeutics and discusses the basics of RNA interference. Additionally, the field of polymeric particulate siRNA carriers is reviewed, with an overview of relevant design criteria for materials intended for pulmonary administration. The advantages of systems capable of triggered payload release are discussed, with an emphasis on acid–sensitive carrier systems. Two acid–sensitive particle systems developed by our group are described.

In Chapter 2, the synthesis of acid–sensitive, acrylamide–based microparticles containing a cell–penetrating peptide (CPP) is discussed. Particles functionalized with a polyarginine CPP are prepared and evaluated for their ability to deliver a model therapeutic payload to non–phagocytic cells. The importance of CPP incorporation on cellular uptake in vitro is investigated in lung epithelial cells. The modification of the microparticles with CPPs greatly improved their uptake by non–phagocytic cells in culture without inducing any cytotoxic effects.

Chapter 3 discusses the role of particle size and functionalization with cationic CPPs on pulmonary delivery using hydrogel particles. The optimal particle design parameters for pulmonary delivery are investigated and the fate of model particles following intratracheal administration is studied by several techniques. Particles are characterized to determine their in vivo behavior in terms of lung retention, localization within specific cell types, and potential for inducing inflammatory responses. We found that altering both size and surface functionalization significantly affected the in vivo behavior of the particle system.

In Chapter 4, we describe the synthesis of a second–generation biocompatible, acid–sensitive particle system for siRNA delivery. The synthesis of spermine–modified acetalated–dextran (Spermine–Ac–DEX) is presented and the preparation of particles with high siRNA loading efficiency is described. The ability of these particles to silence protein expression in vitro is investigated. Spermine–Ac–DEX particles demonstrated efficient gene knockdown in a model cell line with minimal toxicity.

Chapter 5 investigates the synthesis and biological evaluation of functionalizable, acetal–modified dextran, a modular system with tunable functionality, degradation rate, and degree of modification. The preparation of acid–degradable, amine–functionalized dextran is described and the role of type of amine modification (primary, secondary, or tertiary amine) and degradation rate on the efficacy of siRNA delivery is studied in vitro. Altering both the type of amine as well as the degradation rate significantly affected the transfection efficiency. We found that two of the amine–dextrans were able to efficiently deliver siRNA and lead to gene silencing in HeLa–luc cells.

Polymers are extensively used in the field of drug delivery for many applications. The ability to tailor the physical and in vivo properties of polymers allows them to fulfill many roles in drug delivery. Polymers have found value as both direct drug conjugates and coatings of various other delivery systems such as nanoparticles and liposomes. Here, we investigate both types of systems, polymers as liposome coatings and dendrimers directly bound to siRNA.

Chapter 1 presents a brief overview of polymers and macromolecules in the field of drug delivery. Polymeric drug delivery is a very broad and diverse topic, and this chapter mainly addresses areas within the field that relate directly to this dissertation. The history of polymers in drug delivery is presented, and both current capabilities and challenges are discussed.

Chapter 2 describes the synthesis of two disterol poly(ethylene glycol) (PEG) conjugates for the incorporation into liposomes. PEG has the ability to stabilize lipid membranes, extend circulation half-life in vivo, and protect lipid membranes from other unfavorable interactions that may occur in biological settings. Commonly, PEG conjugated to a 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) lipid anchor is used to install PEG onto the surface of lipid monolayers and bilayers. However, PEG-DSPE can phase separate in the membrane surface leading to its possible expulsion from the membrane. Additionally, PEG causes a broadening of the phase transition temperature which makes its use in thermally responsive liposomes challenging. We present the synthesis of two disterol PEG molecules and preliminary characterization of their behavior in lipid membranes.

Chapter 3 is an evaluation of polymers for extended circulation. We investigate the physical and in vivo properties of a panel of polymers for extended circulation on the surface of liposomes as a model platform, although the conclusions drawn are relevant to many types of drug delivery systems. In this chapter we have synthesized well-defined hydrophilic polymers under controlled polymerization techniques and found that all five polymers investigated have lower intrinsic viscosities to that of PEG under consistent experimental conditions. Furthermore, we show that each polymer extends the circulation half-life of liposomes in mice and rats in comparison to conventional liposomes. We also find an immune response and accelerated blood clearance of poly(2‐methyl-2‐oxazoline) (PMOX) coated liposomes upon repeated administration and no such response to the other four polymers in the panel.

Chapter 4 describes the design, synthesis, and in vitro characterization of pH-responsive, biodegradable dendrimers for the delivery of siRNA. Polycationic materials have been extensively investigated for the delivery of RNAi, however, the inherent toxicity of such materials is a major drawback to their use. We envisioned that by installing multiple amines to a dendrimer core through pH-sensitive hydrazone linkages we would be able to circumvent this roadblock to RNAi delivery. Furthermore, by designing a biodegradable dendrimer with orthogonal sets of functional groups, we were able to install other delivery aids onto the dendrimer periphery. In an in vitro firefly luciferase knockdown assay, polymers displayed decreased toxicity in comparison to other cationic delivery strategies and modest knockdown capabilities.

Chapter 5 gives a brief overview of the findings presented in this dissertation followed by a short perspective on the future of polymers in the field of drug delivery.

Molecular level control over macromolecules has been at the heart of human advancement, long before Hermann Staudinger coined the term Makromoleküle. From the development of primitive pharmaceuticals to the advanced materials that sent Man into outer-space, We have been tinkering with God's paint since our inception.

The work described herein primarily involves advances concerning poly-aromatic macromolecules for use in future electronic applications, particularly that of organic photovoltaics. There is a final chapter, however, that gives the reader a taste of how some molecular level changes can be directly visualized with modern microscopy techniques.

Chapter 1 provides a very brief introduction to conjugated polymers and molecular level control over macromolecular properties. Chapters 2 - 4 introduces the concept of polymer substitution as a means by which to control and improve charge generation in organic photovoltaic devices. Chapters 5 and 6 show how these polymers can take on larger, defined structures, yet are still beholden to intrinsic molecular properties - such as regioregularity, a fancy word for the regularity of the position in which two aromatic rings are joined together. Chapter 7 re-examines the role of polymer substitution on photovoltaic performance, this time with an emphasis on homo-polymer packing rather than electron transfer at the donor/acceptor interface. Finally, Chapter 8 visualizes how controlling the environment about a single metal atom can lead directly to a cyclic polyolefin. Individually, these advances do not yield any breakthroughs noticeable to a general audience; collectively, they sit atop a mountain of human knowledge, waiting to provide a stepping stone for the next generation.

The major body of this work investigates how the chemical structure of conjugated polymers relates to the fundamental operating mechanism of organic photovoltaic devices. New conjugated polymers were characterized and their optical and electronic properties tested and correlated with their power conversion efficiencies as the active layer in polymer solar cells. From these experiments general structure/function relationships are drawn with an eye toward developing universal guidelines for conjugated polymer design and synthesis.

Starting with light absorption, three major steps in the photovoltaic mechanism are examined. First, photogeneration of excited states and the migration of these states through the active layer are correlated to the polymeric backbone chemistry and the resulting device performance. Next, separation of these excited states at an interface between electron donors and electron acceptors is examined as a function of donor-acceptor distance and active layer dielectric constant. These two variables were tuned by chemical modification of polythiophene side groups. Third, charge carrier conduction is related to both polymer electronic states and to solid-state packing morphology. Design principles for effective conduction of both holes and electrons are outlined and the ambipolar nature of conjugated organic materials is discussed.

In the final chapters, the solid-state polymer morphology in a solution processed thin film is examined. The impact that this morphology has on all steps in the photovoltaic mechanism is highlighted. How chemical modification of the polymer can influence this packing structure is examined as well as how new fabrication procedures can be used to pre-form nanostructured materials in solution before thin film deposition.

The harvesting of solar energy using photovoltaics has the potential to provide a significant portion of the world's energy. For this to happen, the cost per watt of power produced from photovoltaics must decrease. Excitonic solar cells, including organic solar cells and dye-sensitized solar cells, have the potential to provide the necessary cost savings. However, power conversion efficiencies must be improved before these devices can become practical. This dissertation describes the implementation of several strategies to improve the efficiency of organic polymer and dye-sensitized solar cells.

Chapter 1 provides an introduction to current research on excitonic solar cells with a focus on organic polymer and dye-sensitized cells. The detailed mechanisms of photocurrent generation in each type of cell are discussed, and the factors that determine efficiencies are outlined. In addition, an overview of the progress over the last decade in research on polymer photovoltaics is given. Finally, the future prospects for achieving high efficiency devices are described.

Chapter 2 details a strategy for controlling the morphology of photovoltaic blends of conjugated polymers and small molecule perylene diimide dyes. Blends of these two materials are subject to excessive phase separation that decreases photovoltaic performance. The development of compatibilizers that alleviate this phase separation is described. A diblock copolymer of poly(3-hexylthiophene) (P3HT) and a perylene diimide (PDI) side chain polymer is an effective compatibilizer. Addition of this material to blends of P3HT and PDI suppresses the formation of micron-sized crystals and results in a 50% improvement in solar cell efficiency. The synthesis of a diblock copolymer of poly(3-(4-octylphenyl)thiophene) and the PDI side chain polymer is also described. This material functions as a compatibilizer, but does not allow for improved photovoltaic efficiency.

Chapter 3 describes the synthesis and characterization of a low bandgap conjugated polymer with thermally removable solubilizing groups. Following solution-based deposition of thin films of this polymer, heat can induce the cleavage and evaporation of the alkyl solubilizing chains, resulting in an insoluble film. The optical properties change considerably during this process: the bandgap decreases, and the absorption coefficient increases dramatically. These properties were exploited to fabricate bilayers of the low bandgap material and a highly fluorescent commercial polymer. Fluorescence resonance energy transfer from the fluorescent material to the low bandgap polymer is efficient over 30 nm. Such a scheme could be utilized to overcome the exciton diffusion bottleneck in layered polymer solar cells.

In chapter 4, the synthesis of novel n-type polymers based on PDI monomers is described. With appropriate substitution of alkyl chains, highly rigid perylene benzimidazole ladder polymers can be made soluble in common organic solvents. These materials have exceptionally low-lying LUMOs and possess unusual fluorescence properties. Fully planar perylene ethynylene polymers are also synthesized and characterized. Despite their planarity, data from absorbance and fluorescence spectra suggest that the PDI units in these polymers are poorly coupled electronically. X-Ray diffraction shows that the π-stacking distance varies in these materials depending on the nature of the solubilizing groups and can be decreased through solvent annealing.

Chapter 5 describes how light harvesting can be improved in dye-sensitized solar cells by adding a second dye that transfers energy to the primary sensitizing dye. In liquid cells, incorporation of a PDI dye in the liquid electrolyte solution results in a 28% improvement in power conversion efficiency. Energy transfer is at least 50% efficient despite significant quenching of the perylene dye's fluorescence by the iodide redox couple. Efforts to employ energy transfer in solid-state dye-sensitized solar cells are also described. This is more challenging because the solid-state hole transporter is an excellent quencher of fluorescent dyes. However, it is shown that this quenching can be prevented by self-assembling dyes such as fluorescein 548 into a poly(propyleneimine) dendrimer. Unfortunately, processing conditions that allow the dendrimer/dye conjugates to penetrate the pores of the cell's titania films have not yet been found.