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Part 1: Structure-Property Relationships of Regioregular Poly(3-alkylthiophene)s Bearing Branched Side Chains Part 2: Ferric Chloride-Promoted Oxidative Annulation of 3,3’,4,4’-Tetrahexyloxy-1,1’- biphenyl with Arenes as a Facile Route to Discotic Liquid Crystalline 2,3,6,7,11,12,15,16- Octakis(hexyloxy)diphenanthro[9,10-b:9',10'-d] heteroarenes

(Georgia Institute of Technology, 2023-04-25) Cox, Bronson Evan

Part 1: Structure-Property Relationships of Regioregular Poly(3-alkylthiophene)s Bearing Branched Side Chains Part 2: Ferric Chloride-Promoted Oxidative Annulation of 3,3’,4,4’-Tetrahexyloxy-1,1’-biphenyl with Arenes as a Facile Route to Discotic Liquid Crystalline 2,3,6,7,11,12,15,16-Octakis(hexyloxy)diphenanthro[9,10-b:9',10'-d]heteroarenes Bronson Cox 216 Pages Directed by Dr. David M. Collard Part 1: The first objective of this dissertation was to investigate the influence of branched side chains on the physical and optoelectronic properties of poly(3-alkylthiophene)s. The different branched side chains incorporated into these polymers included a methyl group on the 2-,3-,4-, and 5-positions of a hexyl side chain, and at the 2- and 6-positions on a decyl side chain, and the use of the 2-ethylhexyl side chain. In addition, we sought to ascertain whether the use of these branched side chains might give rise to a thermotropic liquid crystal phase, whereby the polymer could be processed in a fluid, ordered melt to attain control over the alignment of the backbone and thereby enhance charge transport. Part 2: The second objective of this dissertation was to investigate a novel and straightforward approach for synthesizing new diphenanthro-fused heteroarenes. We synthesized these compounds by FeCl3-promoted oxidative annulation of 3,3’,4,4’-tetra(alkyloxy)biphenyl with 2-bromothiophene or pyrrole. We characterized the physical and optoelectronic properties of the products by NMR, UV-vis, and fluorescence spectroscopies, as well as by DSC and POM.
Multi-tiered Conjugated Oligomers as Models to Mimic Pi-Pi Interactions in Semiconducting Conjugated Materials

(Georgia Institute of Technology, 2021-09-28) Johns, Ashley Elisabeth

The electronic structure of semiconducting π-conjugated materials continues to attract interest through both experimental and theoretical approaches. To explore the effects of intermolecular interactions between conjugated systems, we have embarked on an examination of the electronic structure of a series of molecules in which conjugated segments are held in a stacked arrangement. This arrangement mimics face-to-face packing of segments in the crystalline region of conjugated polymers. We report the use of [2.2]paracyclophane as a scaffold to create multi-tiered oligo(phenylene ethynylene)s. By substituting [2.2]paracyclophane in a pseudogeminal (pg) pattern with oligo(phenylene ethynylene)s, conjugated segments are held atop one another in a stacked manner consisting of a number of tiers. We have also explored the use of 1,8-disubstituted anthracene as a molecular scaffold to hold oligo(phenylene ethynylene) segments in a stacked arrangement. One-tier, two-tier, and three-tier structures were prepared. The effects of π-π stacking on electronic structure were studied through multiple methods. The oligomers are characterized using UV-Vis and fluorescence spectrometry and by voltammetry techniques to determine the evolution of optoelectronic properties as conjugated oligomers are assembled into multi-tiered architectures.
Design and synthesis of new fused arene- containing conjugated polymers

(Georgia Institute of Technology, 2018-09-13) Kulkarni, Chinmay R.

Conjugated polymer have attracted attention in the past two decades because of a range of advantages over inorganic – semiconductors. They can be solution processed, they offer flexibility, and their electronic structure can be tuned through molecular design. These characteristics make them applicable in solar cells, light-emitting diodes and transistors. There are few examples of conjugated polymers that contain simple acenes (e.g., naphthalene, anthracene, pentacene). One of the key challenges to the incorporation of acene units is the need to retain solubility of the polymers. This requires the multistep synthesis of acene monomers bearing flexible alkyl or alkoxy groups. Conjugated polymers containing aromatic units have two non-degenerate ground states that are referred to as the aromatic and quinoidal forms. The quinoidal form is higher in energy and can be stabilized by fusion of a benzene ring onto the aromatic unit of the conjugated backbone. The stabilization of the quinoidal form impacts the band gap of conjugated polymers, as demonstrated by the low band gap of polyisothianaphthalene, which is ~1 eV lower than that of polythiophene. In chapter two, the effect of the incorporation of acenes into poly(arylene ethynylene)s is explored through the preparation and characterization of a series of copolymers. It was found that the incorporation of a 9,10-anthracene unit significantly lowers the bandgap compared to analogs containing 1,4-phenylene and 1,4-naphthalene units. This can be understood in terms of the stabilization of the quinoidal form of the anthracene-containing polymers compared to the phenylene and naphthalene-containing analogs. The stabilization of quinoid form arises from the fusion of benzene rings onto the phenylene ring in the conjugated backbone. In chapter three, the impact of in the incorporation of naphthalene and anthracene units on the electronic structure of alternating donor-acceptor polymers with N,N-disubstituted naphthalenediimide (NDI) units is explored. In this series of polymers it was observed that the anthracene-containing polymer displayed a significantly red-shifted charge transfer type transition compared to phenylene and naphthalene containing polymers. This may be understood to arise from the stabilization of quinoidal form of the anthracene-containing conjugated polymer. In chapter four, approaches to the synthesis of tetraalkoxy-substituted anthracene monomers for synthesis of anthracene-containing (arylene vinylene) polymers are discussed.
Processing components in π-conjugated polymers: Controlling solubility, morphology, and functionality through structural design

(Georgia Institute of Technology, 2018-07-02) Schmatz, Brian J.

Over the past 30 years conjugated polymers have demonstrated performance strides in solution-printed photovoltaics, transistors, displays, and sensors. With fundamental structure-property relationships in place, the next step is to prepare these materials for use in large-scale, high-throughput printing facilities where reproducibility, tolerance to the environment, safety, and sustainability will all play a pivotal role in the ultimate success of conjugated polymer based electronics. This dissertation explores how to achieve that next step through the use of processing components, or structural moieties that embed a desired processing property. Chapter 1 provides an introduction to the design, fundamental properties, and methods of processing soluble conjugated polymers, placing specific emphasis on the interplay between molecular structure, processability, and ultimately performance. Polymer synthesis, characterization, and processing methodology unique to this dissertation are presented in detail in Chapter 2. Chapter 3 describes the use of triphenylamine as a processing comonomer in dioxythiophene polymers. The triphenylamine comonomer templates an amorphous thin-film morphology by embedding backbone torsion and conjugation breaks, providing reproducible films that are tolerant to fluctuations in processing conditions. Chapter 4 explores the use of polymer side chains with multiple functionalities, or multistage side chains, to control solubility for aqueous printable conjugated polymers. Finally, Chapter 5 delves into the intricate morphological effects of polymer side chain placement in organic photovoltaic donor-acceptor blends. Specifically, the study utilizes a novel family of donor-acceptor polymers with methylated acceptor monomers to observe how side chain steric interactions affect morphology and optoelectronic properties in blends of polymeric donors and molecular acceptors.
Synthesis of functional polylactides for biomedical and pharmaceutical applications

(Georgia Institute of Technology, 2018-03-30) Kalelkar, Pranav Pratap

Polylactide (PL) is an aliphatic thermoplastic that has gained attention over the years as a result of it biocompatible and biodegradable behavior. These characteristics make PL an attractive material for use in biomedical devices and medical implants. However, the lack of functional groups along the backbone limits its applications. To overcome this limitation, I have synthesized five new functional copolylactides that bear reactive functional groups such as chloride, bromide, thiol, azide and electron-deficient alkenes. Incorporation of functional groups allow for post-polymerization modification using mild chemistry such as azide-alkyne click chemistry, thiol-ene click chemistry and atom-transfer radical polymerization. I have fabricated thin films and nanoparticles of selected materials to provide preliminary demonstration of these copolymers to bioconjugation, drug delivery and antimicrobial activity.
Controlled doping of organic semiconductors and 2d materials with molecular reductants and oxidants

(Georgia Institute of Technology, 2016-07-12) Zhang, Siyuan

New air-stable dimeric n-dopants are synthesized and studied in detail with respect to the kinetics of both their redox reaction in solution with and their doping in the solid-state of various organic semiconductor acceptors. Detailed mechanistic studies are necessary to recognize the strengths and limitations of existing dimers to inform future dopant design. The newly synthesized n-dopants together with other redox-active n- and p-dopants are then used to surface modify mono- and multi-layer graphene, which shows a large decrease in the sheet resistance and tunable work function shifts. A subset of these molecules is applied to MoS2 and WSe2 to realize controllable n- and p-doping, respectively, to improve their electrical properties. Other experimental techniques, especially UPS and XPS, are coupled with the electrical measurements to give information about work function shifts, surface coverage, charge transfer efficiency, and etc. Finally, organic diodes, solar cells, and field-effect transistors with doped graphene electrodes were fabricated, where the work function engineering of graphene electrodes via doping proved to be important in reducing the carrier-injection barriers.
Ring-opening benzannulations of cyclopropenes, alkylidene cyclopropanes, and 2,3-dihydrofuran acetals: A complementary approach to benzo-fused (hetero)aromatics

(Georgia Institute of Technology, 2016-05-27) Aponte-Guzman, Joel

Over the past decades, functional group manipulation of aromatic precursors has been a common strategy to access new aromatic compounds. However, these classical methods, such as Friedel-Crafts alkylations and electrophilic/nucleophilic aromatic substitutions, have shown lack of regioselectivity besides the use of activators in excess amounts. To this end, numerous benzannulations to form benzo-fused substrates via Diels-Alder (DA), ring-closing metathesis (RCM), cycloaddition, and transition-metal-promoted processes have been reported. Appending a benzene ring directly onto a pre-existing ring is preferable to many classical methods due to the likely reduction of reaction steps and superior regiocontrol. However, many of these benzannulation reactions require air- and/or moisture- sensitive reaction conditions, a last oxidation step, or the use of highly functionalized precursors. Here we disclose three ‘complementary’ intramolecular ring-opening benzannulations to access a large array of functionalized (hetero)aromatic scaffolds utilizing cyclopropenes-3,3-dicarbonyls, alkylidene cyclopropanes-1,1-diesters, and 2,3-dihydrofuran O,O- and N,O- acetals as building blocks. More than 70 benzo-fused aromatic compounds were synthesized using this complementary approach with yields up to 98% and low catalyst loadings. With these benzannulation reactions in hand, we aim to open the synthetic door to a handful of bioactive natural products.
Design and synthesis of and π-stacked conjugated oligomers and polymers

(Georgia Institute of Technology, 2012-03-16) Jagtap, Subodh Prakash

Interchain interactions between π-systems have a strong effect on the properties of conjugated organic materials that find application in devices such as light emitting diodes (OLEDs), organic photovoltaics (OPVs), and field effect transistors (FETs). We have prepared covalently-stacked oligo(1,4-phenylene ethynylene)s and oligo(1,4-phenylene vinylene)s to study the influence of chain-chain interactions on the electronic structure of closely packed conjugated units. These serve as models for segments of conjugated materials in thin film devices. Extension of this concept has allowed us to prepare multi-tiered systems that display the influence of pi-stacking. The stacked architectures were prepared by multi-step synthesis of the scaffolds, followed by metal-catalyzed cross coupling reactions (Sonogashira, Heck, Suzuki couplings) to incorporate the conjugated oligomers. The optical and electrochemical properties of these stacked compounds and polymers were compared to their unstacked linear counterparts. These studies provide a platform for the exploration of the nature of charge carriers and excitons in a broad class of materials that have significant potential in addressing challenges in power generation, lighting and electronics.
Design, synthesis and characterization of self-assembling conjugated polymers for use in organic electronic applications

(Georgia Institute of Technology, 2011-03-23) Woody, Kathy Beckner

Conjugated polymers comprise some of the most promising materials for new technologies such as organic field effect transistors, solar light harvesting technology and sensing devices. In spite of tremendous research initiatives in materials chemistry, the potential to optimize device performance and develop new technologies is remarkable. Understanding relationships between the structure of conjugated polymers and their electronic properties is critical to improving device performance. The design and synthesis of new materials which self-organize into ordered nanostructures creates opportunities to establish relationships between electronic properties and morphology or molecular packing. This thesis details our progress in the development of synthetic routes which provide access to new classes of conjugated polymers that contain dissimilar side chains that segregate or dissimilar conjugated blocks which phase separate, and summarizes our initial attempts to characterize these materials. Poly(1,4-phenylene ethynylene)s (PPEs) have been used in a variety of organic electronic applications, most notably as fluorescent sensors. Using traditional synthetic methods, asymmetrically disubstituted PPEs have irregular placement of side chains on the conjugated backbone. Herein, we establish the first synthetic route to an asymmetrically substituted regioregular PPEs. The initial PPEs in this study have different lengths of alkoxy side chains, and both regioregular and regiorandom analogs are synthesized and characterized for comparison. The design of amphiphilic structures provides additional opportunities for side chains to influence the molecular packing and electronic properties of conjugated polymers. A new class of regioregular, amphiphilic PPEs has been prepared bearing alkoxy and semifluoroalkoxy side chains, which have a tendency to phase separate. Fully conjugated block copolymers can provide access to interesting new morphologies as a result of phase separation of the conjugated blocks. In particular, donor-acceptor block copolymers that phase separate into electron rich and electron poor domains may be advantageous in organic electronic devices such as bulk heterojunction solar cells, of which the performance relies on precise control of the interface between electron donating and accepting materials. The availability of donor-acceptor block copolymers is limited, largely due to the challenges associated with synthesizing these materials. In this thesis, two new synthetic routes to donor-acceptor block copolymers are established. These methods both utilize the catalyst transfer condensation polymerization, which proceeds by a chain growth mechanism. The first example entails the synthesis of a monofunctionalized, telechelic poly(3-alkylthiophene) which can be coupled to electron accepting polymers in a subsequent reaction. The other method describes the first example of a one-pot synthesis of a donor-acceptor diblock copolymer. The methods of synthesis are described, and characterization of the block copolymers is reported.
Synthesis and properties of π-stacked phenylene ethynylene oligomers with a 1,8- substituted naphthalene bridging scaffold

(Georgia Institute of Technology, 2010-05-11) Carson, Bradley Edward

The field of molecular electronics includes the study of conjugated oligomers and polymers that have significant potential for use in devices such as light emitting diodes (LEDS), field effect transistors (FETS), and photovoltaic solar cells. These materials may replace inorganic semiconductors in these devices, Achieving better device performance through lowering the band-gap and achieving higher field effect mobilities will benefit from a greater fundamental understanding of charge transfer through the aromatic subunits. π-stacking of segments of conjugated polymers has been identified as a key feature that influences the charge transfer through semiconducting organic materials. Optimizing the molecular architecture of conjugated polymers has the potential to provide materials with better charge mobility. While devices might benefit from materials that take advantage of π-stacking, access to π-stacked structures presents a synthetic challenge. 1,8-Disubstituted naphthalenes may serve as simple covalent bridging scaffolds which might hold conjugated oligomers in a π-stacked arrangement. The research described in this thesis focuses on the synthesis of well-defined phenylene ethynylene oligomers coupled to naphthalene to serve as experimental models of closely π-stacked aromatic units in conjugated polymers. The π-stacked molecules reported in this dissertation are characterized by NMR, IR, and mass spectrometry. The effects of π- stacking on the structure and behavior of conjugated oligomers are determined by X-ray crystallography, spectroscopy, and electrochemistry.