Conjugated Polymers in Thermoelectric Composites and Small Molecules for High Light Absorptivity

Over the past several decades with increasing of global energy demand, thermoelectric materials have gained considerable attention due to their unique ability to directly convert heat to electricity. In addition to inorganic semiconductors, polymers are potential candidates for high-performance thermoelectric applications due to their intrinsic advantages such as low thermal conductivity, solution processability, and roll-to-roll production, lightweight, and flexible thermoelectric modules. This thesis provides an insight into the emerging field of organic thermoelectrics, more specifically, thermoelectric power generation based on the composites of conducting polymers (MEH-PPV, P3HT and PEDOT:PSS) and carbon nanotubes (SWNT, SWNT-COOH, SWNT-OH and MWNT). A substantial portion of my work at the graduate level has involved the composite materials of conductive polymers and carbon nanotubes (CNTs) for use in organic thermoelectrics (TE). This work comprised multiple iterations to test effects of chain length (molecular weight) and regioregularity, amount and type of CNT added, sample fabrication solvent, and doping duration led to substantial optimization of the TE power factors. A power factor of 148 μW m-1 K-2 was obtained in the optimized sample preparation with rr-P3HT-Rieke/50%SWnNT which is quite competitive with the PFs mentioned in section 2.3. Besides polymers, I also investigated TE properties of cross-linked network structures established from UV curable small molecules with CNTs. A variety of distinct morphological architectures -- consistent with differences in TE performances -- have been observed. I described the synthesis of new pyridinium and extended viologen molecules capturing light in the visible portion of the solar spectrum with high molar extinction coefficient (~22,000 to 278,000 M-1 cm-1) by means of intramolecular charge transfer (ICT), using electron-donor and electron-accepter groups linked through π-conjugation. Also, these compounds exhibited solvatochromic properties in absorption and emission spectra with respect to the ICT band

Towards supramolecular heterojunctions : self-assembled hydrogen-bonded architectures for organic photovoltaic devices

Ces travaux ont pour but la conception et la synthèse de composants moléculaires photo-et électro-actifs programmés l’auto-organiser en hétérojonctions supramoléculaires actives en conversion photovoltaïque. L’utilisation de fullerène (C60) et d'oligothiophène portant des motifs de reconnaissances moléculaires par liaisons hydrogène permet la conception d’architectures supramoléculaires en ruban, optimisées pour la séparation et la transport de charges efficaces. L’étude de monocouches auto-assemblées portant des groupes de reconnaissance moléculaires permet de structurer la couche active et augmente la réponse photovoltaïque des dispositifs. La fabrication de cellules solaires organiques à l’état solide avec ces matériaux auto-assemblées a également été étudiée.The aim of this research is to focus on the implementation of supramolecular self-assembly of photo-and electro-active components programmed to self-organize into molecular heterojunctions for efficient light-to-electrical energy conversion. The incorporation of fullerene and oligothiophene appended with complementary hydrogen-bonding molecular recognition motifs allows the design of supramolecular architectures engineered to achieve efficient charge separation and transport. In addition, the incorporation of self-assembled monolayers bearing hydrogen-bonding molecular recognition end-groups on electrode surface further enhances the photovoltaic response of the functional supramolecular devices. The fabrication of solid-state organic solar cells with the self-assembled photoactive materials also has been investigated

Synthesis and characterizations of pyridinium salts including poly(pyridinium salt)s and their applications

Pyridinium salts, both molecular and polymeric, are an interesting class of multifunctional materials that exhibit liquid-crystalline and light-emitting properties. Moreover, their properties can be easily tuned by introducing new types of anions or by modifying their chemical structures. This dissertation describes synthesis and characterization of poly(pyridinium salt)s containing macrocounterions and fluorene moieties in their backbones, synthesis and characterization of nanocomposites of poly(pyridinium salt)s with single-walled carbon nanotubes via non-covalent interactions, and synthesis and characterizations of pyridinium salts having different aliphatic linkages and their application in organic acid sensing. First, all of these ionic polymers were prepared by either ring-transmutation or by metathesis reaction. Their chemical structures were established by FTIR, 1H spectroscopy and elemental analysis. Some polymers containing macrocounterions had relatively low melting transitions above which they formed thermotropic liquid-crystalline phase; and other polymers were amorphous as determined by VTXRD studies. Ionic polymers containing fluorene moieties in their backbones exhibited lyotropic properties in both polar protic and aprotic solvents at various critical concentrations. Light emission properties of this class of polymers in common organic solvents as well as in water and in solid states were also studied. To explore the application of poly(pyridinium salt)s, we developed a method of preparation of nano-composites with a number of poly(pyridinium salt)s and single-walled carbon nanotubes. The single-walled carbon nanotubes were effectively dispersed with various poly(pyridinium salt)s resulting in nanocomposites. The optical and solution properties of these composites were examined by a number of experimental techniques. Finally, some of the synthesized dicationic salts exhibited ionic liquid properties, but all exhibited fluorescent properties in solution and solid states. Due to the presence of methyl orange counterions, pyridinium salts could serves as a pH sensor in organic solvents

Electronic transport in nano-scale organic semiconductors from non-adiabatic molecular dynamics

New electronic devices fabricated from organic molecules have been greatly improved over the past two decades. Yet, understanding the electronic transport mechanism of free carriers and excitons (bound electron-hole pairs) in organic semiconductors (OSs) is still a pertinent challenge. The soft molecular nature of these materials gives rise to an intricate interplay between electronic and nuclear motion as well as unique solid-state physical properties. Standard (analytic) treatments describing electronic transport often rely on one of two extremes: a travelling wave propagating through the material or a particle hopping from one molecular unit to the next. These are often unsuitable to fully describe the complex dynamics, which falls in between these regimes. In this regard, non-adiabatic molecular dynamics simulations permit a direct view into the transport mechanism, thus providing new important insights. In this thesis, I have further developed and improved in terms of efficiency and accuracy a fully atomistic non-adiabatic molecular dynamics algorithm, called fragment orbital-based surface hopping (FOB-SH). This allows the propagation of the coupled electron-nuclear motion in large nano-scale systems. After validating the accuracy of this methodology and discussing important physical requirements (i.e. energy conservation, detailed balance and internal consistency), I will present the application of FOB-SH to the calculation of room temperature charge mobility of a series of molecular organic crystals. I will discuss the agreement with experimental mobility values and the role of the disorder, induced by thermal fluctuations, on the delocalization of the states and the subsequent formation of a polaronic charge state. This polaronic charge propagates through the crystal by diffusive jumps over several lattice spacings at a time during which expands to more than twice its size. I will show that FOB-SH can recover the crossover from hopping to band-like transport depending on the strength of the electronic coupling and the temperature, thus successfully bridging the gap between these two extreme transport regimes. Finally, I will discuss a further extension of FOB-SH to the treatment of exciton transport in OSs. This opens up new exciting avenues for the application of FOB-SH to the study of electronic processes occurring in organic photovoltaic cells

Supramolecular Luminescent Sensors

There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed

New methodologies for sustainable organic synthesis in water.

Water is stable, benign, and green solvent. Its usage as a solvent in organic synthesis is significantly enhanced by micellar catalysis. However, replacing water as a reaction medium in organic synthesis is not sufficient to meet the sustainability challenges—excessive organic solvents are still required for product isolation and purification. Notably, solvents used in syntheses contribute to more than 80% of waste generation. In addition to solvents, the use of palladium in large amounts is also a problem for the future as it is a precious, low-abundance metal, and its supply is dwindling. Therefore, this dissertation highlights the various sustainable protocols for minimization of the usage of solvents, incorporation of nanocatalysis using earth-abundant first-row transition metals, and development of highly selective protocols for amide couplings, cycloaddition reactions, cross-couplings, and monofluorination of N-heterocycles respectively. Chapter 1 reviews the importance of Green and Sustainable Chemistry, highlighting its impact on the cost and waste reductions in various industrial organic transformations. It also includes the concept of micellar catalysis (reaction in water) in combination with nanocatalysis for efficient cross-couplings. Moreover, the future directions and present challenges in the field of green chemistry are emphasized. Chapter 2 discusses the development of a novel protocol for the monofluorination of bioactive N-heterocycles. The current methodology suffers from low yields with the formation of genotoxic byproduct (with a permissible limit of Chapter 3 highlights an unprecedented methodology for the selective monofluorination of unprotected indoles under mild aqueous conditions. The methodology is easy to execute and does not require the use of toxic organic solvents or rare-earth metals. High selectivity towards monofluorinations was achieved on a broad range of substrates, including the synthesis of intermediates of bioactive molecules. Chapters 4 & 5 discuss the sustainable protocol for the amide couplings in water. It highlights the use of our designer surfactant PS-750-M, which structurally mimics toxic dipolar-aprotic organic solvents like DMF, DMAc, and NMP. PS-750-M along with coupling agent forms mixed micelles, which enable ultrafast amide couplings in water. The most common coupling agent used in amide couplings is 1-Ethyl-3-(3-(dimethylamino)propyl)-carbodiimide (EDC•HCl). It has both lipophilic and hydrophilic regions allowing its self-aggregation in an aqueous medium containing PS-750-M to form mixed micelles. These mixed micelles provide a very high local concentration of reactants, resulting in ultrafast reaction rates without product epimerization. The methodology completely avoids the use of toxic organic solvents as the product spontaneously extrudes out of micelle, allowing its isolation by simple filtration. Chapter 6 describe the use of sustainable and inexpensive Cu(I) catalysis for cycloadditions. Notably, spontaneous oxidation of Cu(I) to Cu(II) adversely affects the reaction efficiency. We developed a catalytic methodology that uses Cu(II) nanomaterial, light, and azide. The irradiation triggers the single electron transfers from azide to Cu, generating Cu(I) species within the micelles to enable powerful cycloaddition chemistry via Cu(I) catalysis. Nanomaterial was characterized using XAS, HRTEM, NMR, UV-Vis, and IR spectroscopy. Chapter 7 discusses a completely organic solvent-free technology for copper-catalyzed cycloadditions, using a benign cellulose-based polymer, hydroxypropyl methylcellulose (HPMC). The unique hydrophobic pockets of HPMC enable the formation of ultrasmall water-stable Cu(I) NPs which was used for the fast organic solvent-free cycloadditions in water. Chapters 8 & 9 describe the development of new (bi)trimetallic nanoparticles (NPs). These NPs exhibit the synergy between two or more metals that enable powerful, sustainable, and selective catalysis. The bimetallic NPs of Cu and Mn, as well as trimetallic NPs of Cu, Mn, and Pd (ppm level) enable selective Suzuki-Miyaura cross-coupling, hydroboration and hydrosilylation of alkenes, alkynes, and chalcones. All these transformations were carried out under mild aqueous conditions. Chapter 10 highlights the synthesis of metal-free organic polymer and its applications in the E to Z isomerization of olefins. The photocatalyst is highly recyclable (up to 4 cycles). The methodology was also extended for the esterification of aldehydes and oxidations of alcohols under aqueous medium

Development of new functional food traits in peanuts

Two categories of functional food traits were researched: dietary minerals and antioxidants. The primary objectives were to (1) characterise diverse peanut phenotypes using established methods or developing and validating analytical methods if necessary; (2) estimate genotypic variation in the functional food trait; and (3) investigate the stability of the functional food trait through studies of genotype-by-environment (G × E) interaction. Essential mineral concentrations in kernels were analysed by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and ICP-mass spectrometry (ICP-MS) with the use of a dynamic reaction cell (DRC) after preparation of samples by microwave-assisted closed acid digestion. Antioxidant capacity was assessed using ABTS +, DPPH , Folin-Ciocalteu total phenolics, and ORAC assays adapted to a 96-well microplate format for high-throughput analysis. The phytochemical profile was quantitatively analysed by high performance liquid chromatography (HPLC) with the use of a photodiode array (PDA) detector, after ultrasound- and enzyme-assisted extraction and solid phase extraction to purify and concentrate the extracts. Genotypic variation for essential minerals and antioxidant capacity was estimated by analysis of 32 full-season maturity and 24 ultra-early maturity genotypes from the Australian Peanut Breeding Program (APBP). The studies established useful levels of variation of more than 10% relative standard deviation (RSD) among the genotypes in concentrations of most of the tested essential minerals, and of more than 20% RSD in antioxidant capacity, although only the ORAC assay distinguished statistically significant differences between genotypes. Studies of G × E interaction affecting the essential mineral and antioxidant capacity traits revealed that genotype, environment, and G × E interaction all significantly affected trait expression. The results confirmed that there was substantial genetic control of essential mineral concentrations and antioxidant capacity in peanut kernels, but that it will be important to characterise environmental interaction to enable plant/seed selection in the APBP and potentially manipulate the interaction through agronomic or postharvest management. The essential minerals data were used to develop approximately predictive calibrations for Ca, K, Mg, and P by near-infrared reflectance spectroscopy (NIRS) of sufficient accuracy to be useful as plant/seed selection tools in plant breeding. Techniques that enable high-throughput, non-destructive, time/cost-effective analysis of trait segregation are valuable due to the extremely large number of samples that are generated in breeding programs. Five peanut genotypes with diverse antioxidant capacity phenotypes were quantitatively profiled for p coumaric acid, salicylic acid, resveratrol, and daidzein. The co-eluting compounds, caffeic/vanillic acid and ferulic/sinapic acid, were quantified on caffeic acid equivalent and ferulic acid equivalent bases, respectively. The HPLC analysis established significant genotypic differences in phytochemical concentrations and also the importance of the bound (e.g., conjugated and matrix-embedded) fraction. Fractions of the HPLC eluate were evaluated by ORAC assay to evaluate relative contributions to antioxidant capacity, and allowed identification of a number of unknown compounds that made important contributions to antioxidant capacity. HPLC analysis of kernels subjected to various roasting treatments (150 °C, 0-70 min and 160 °C, 0-32.5 min) showed that ferulic/sinapic acid concentrations declined with roasting duration, but that most other tested analytes were relatively thermo-stable