The molecular design, synthesis, spectroscopic and photophysical characterization of a series of cyanostilbene-based compounds are studied in this thesis. The thermal, electrochemical and aggregation induced emission (AIE) properties of these cyanostilbene-based compounds, as well as their application in organic lighting-emitting diodes, live cell imaging, chemical vapor sensor were investigated. Chapter 1 gives a brief introduction on the aggregation-caused quenching (ACQ) behavior of the conventional organic luminogens and the discovery and proposed mechanism of AIE phenomenon. Furthermore, some examples and the applications of these AIE compounds will be discussed. In Chapter 2, triphenylamine- and carbazole-containing cyanostilbene-based derivatives are presented. From the examination of the emission profile, they are all AIE-active through comparison of the photoluminescence intensity in dissolved and in aggregated states. Additionally, the calculation of the enhancement ratio (I/I0 – 1) of each fluorophore was performed in order to quantify its AIE effect. One of our cyanostilbene-based luminogens has achieved an enhancement ratio with a value of 1128. This cyanostilbene-based luminogens has also shown good performance in OLED investigation. In addition to the OLEDs application, the selected cyanostilbene-based luminogens with solid-state emission, cell-permeability and reversible switch-on/off capability have illustrated the positive result in live-cell imaging and chemical vapor sensing. Conjugated polymer with high molecular weight is the superior option by overcoming the weaknesses of low-molecular-weight luminogens with excellent thin-film form ability and comparatively simple and inexpensive fabrication processes. The design and synthesis of the cyanostilbene-based polymeric chromophores are described in Chapter 3. The polymerization of the AIE-active diacetylene ligands by connection of trans-[Pt(PBu3)2] unit at both ends has successfully retained their AIE behavior. In contrast, the ACQ problem has occurred on the polymers with organic spacers and the AIE-active ligands. From the DFT calculation on the Pt polymers and the blue shift of emission spectra in high water content suggested that the AIE phenomenon of Pt polymers is probably originated from the elimination of the non-radiative intramolecular charge transfer (ICT) process. Owing to the high demand in red-emitting materials in the applications of electroluminescent devices, fluorescent sensing and bio-imaging, effort has been made to design a system with the new chromophores with donor (D) – acceptor (A) system and thus to synthesize phenothiazine (D)-containing cyanostilbene (A)-based derivatives which are depicted in Chapter 4. Consistent with the conventional AIE-active luminogens with a successively climb of photoluminescence intensities in response to the increase of water proportion, phenothiazine-containing cyanostilbene-based derivatives has exhibited a V-shape fashion of emission intensity. It suggests that the emission of chromophores started to be quenched due to the increase of solvent polarity, overriding that of the molecular aggregation when a “small” volume of water is being introduced. While aggregate formation was dominant from the addition of a “large” amount of poor solvent, less polar local environment was created which suppressed the non-radiative transition to the ICT state and intensified the emission efficiency. Phenothiazine (D) – cyanostilbene (A) system has created a series of red-emitting chromophores with great tunability for the sake of achieving the desired emission color and better emission efficiency. To functionalize these AIE-active cyanostilbene-based chromophores, pyridine group was attached to the compounds to take the advantage of its metal-chelating capability, which is discussed in Chapter 5. The AIE features of cyanostilbene-based compounds can be preserved after the introduction of the pyridyl unit. Even it possessed a weak photoluminescence in its dilute solution which suggest that the high electron delocalization within the molecule has rigidified the structure to some extent, it is transformed to a highly emissive state with a high proportion of water. The exclusive variation of emission behavior with obvious bathochromic shift and boost of emission spectrum in the presence of cadmium-(II) ion has demonstrated its potential metal ion sensing ability. Chapter 6 and 7 present the concluding remarks and the experimental data of the compounds of Chapter 2 to 5, respectively.

Pour mieux comprendre les éléments du métabolisme impliqués dans la détectionélectrochimique de bactéries et dans les biopiles bactériennes, le comportementélectrochimique de différentes souches de bactéries de type E. coli a été analysé. Lesbactéries ont été incubées dans un milieu de culture en présence de différents substrats,dans une cellule électrochimique à 3 électrodes où l’électrode de travail (ITO) agit en tantqu’accepteur d’électrons. En utilisant la voltampérométrie cyclique et lachronoampérométrie, l’accès aux caractéristiques électrochimiques des médiateurs redoxissus du métabolisme bactérien a ainsi pu être réalisé. Dans le cas des bactéries de typeE.coli XL1-Blue incubées en présence de sources différentes de carbone, telles que leglucose, le succinate ou l’acétate, il a été montré que les bactéries produisent un médiateurredox naturel, quelle que soit la source de carbone. Un courant électrique plus importantest obtenu dans le cas où un médiateur redox (PQQ or riboflavine) est ajouté dans lemilieu. Dans le cas des bactéries de type E.coli K12 et de ses souches mutantes ΔmenC etΔubiC incubées en présence de glucose ou de succinate, il a été trouvé que la soucheΔubiC produit un courant électrique plus élevé que E.coli K12 et ΔmenC. Il sembleraitainsi que la souche ΔubiC présente une activité électrochimique faisant intervenir un gènede régulation de la voie de synthèse de la ménaquinone. / To further understand the metabolism parameters involved in the electrochemicaldetection of bacteria and microbial fuel cell applications, the electrochemical behavior ofdifferent E. coli strains was analyzed. The bacteria were incubated in anaerobic conditionin a culture medium containing different substrates in a three-electrode electrochemicalcell where ITO working electrode serves as an electron acceptor. Using cyclic voltammetryand chronoamperometry, the electrochemical characteristics of excreted redox compoundsissued from bacterial metabolism have been assessed. In the case of E. coli XL1-Blue inpresence of different carbon sources such as glucose, succinate or acetate, the resultsshowed that a natural redox compound is produced whatever the carbon source. A higherelectrical current is obtained in the case of the addition of artificial mediators (PQQ orriboflavine) in the medium. In the case of E. coli K12 and its mutants ΔmenC and ΔubiCincubated in medium containing glucose or succinate, it is found that ΔubiC produced ahigher current compared to E.coli K12 and its mutants ΔmenC. It has been proposed thatΔubiC exhibits its electrochemical activity through the gene regulation of menaquinonesynthesis pathway.

Screen printed electrodes (SPEs), which are prepared by patterning conductive inks or pastes onto an insulating support (e.g., plastic film), are widely employed as sensing and biosensing platforms due to their ease of fabrication and relatively low cost. This is especially applicable to electrodes of this nature prepared with carbon-based inks (SPCEs). To date, the most successful and significant commercial application of SPEs has been as test strips for glucose meters. Despite the maturity of this technology, SPE research remains very active as improvements in sensitivity and selectivity, which often involve modifying the electrode surface, hold the key to advancing their utility in routine applications and extending their benefits to other target analytes. Recent studies in the Bishop research group have demonstrated that nitrogen-doped SPCEs (N-SPCEs) exhibit enhanced electrochemical response towards hydrogen peroxide (H2O2), a product of oxidase enzyme (e.g., glucose oxidase, lactate oxidase, etc.) reactions and a common target in biosensing strategies. The presence of nitrogen heteroatoms on the carbon surface facilitates breakage of oxygen-oxygen bonds, a key step in reduction of H2O2. Since previous studies showed only modest incorporation of nitrogen species on SPCEs prepared from commercial ink, these studies aim to investigate the possibility of enhancing N-doping by performing a simple pre-treatment strategy that reportedly increases surface oxygen content of SPCEs prior to N-doping. Since surface oxygen sites have been previously reported to be preferentially modified with nitrogen during N-doping strategies, this seems like a promising technique for improving sensitivity of N-SPCEs for H2O2 reduction. To quantify the actuality of these claims, experimental groups were fabricated having undergone no enhancement, pretreatment enhancement only, nitrogen-doping enhancement only, and a combination of the pretreatment and nitrogen-doping enhancements. Here the electrochemical behaviors of pretreated SPCEs, N-SPCEs, and pretreated N-SPCEs for the detection of H2O2 by completing comparative cyclic voltammetry (CV) experiments with and with out the presence of H2O2 and with it present in varying concentrations is compared. It is projected that, if successful, the fabricated electrodes that have undergone both the pretreatment protocol and the nitrogen-doping process will have an increased sensitivity and detection limit towards H2O2.

Electrochemical measurements are utilized in various fields, including healthcare (e.g., potentiometric measurements for electrolytes in blood and blood gas, amperometric biosensing of glucose as in blood glucose meters), water quality (e.g., pH measurement, voltammetric analyses for heavy metals), and energy. Much of the appeal of electrochemical analyses can be attributed to the relative simplicity, low cost and lack of maintenance associated with electrochemical instruments, along with techniques that can exhibit high sensitivity and selectivity, wide linear dynamic range, and low limits of detection for many analytes. While commercial electrochemical analyzers are less expensive than many other instruments for chemical analyses and are available from various manufacturers, versatility and performance often coincide with added expense. Recently, the development of low-cost, adaptable, open-source chemical instruments, including electrochemical analyzers, has emerged as a topic of great interest in the scientific community. In contrast to commercial instruments, for which schematics and underlying operation details are often obscured – severely limiting modifications and improvements, creators of open-source instruments release all the necessary information for reproduction of the hardware and software. As a result, open-source instruments not only serve as excellent teaching tools for novices to gain experience in electronics and programming, but also present opportunity to design and develop low-cost, portable instruments, which have particular significance for point-of-care sensing applications, use in resource-limited settings, and the rapidly developing field of on-body sensors. In this work, we report the design of a low-cost, compact electrochemical analyzer based on an open-source Arduino microcontroller. The instrument is capable of performing electrochemical analyses such as cyclic and linear sweep voltammetry with an operating range of ± 138 ��A and ± 1.65 V. Performance of the platform is investigated with low-cost pencil graphite electrodes and results compared to commercial potentiostats.

Abstract Electrochemical sensors are simple, fast, accurate, and low-cost analytical devices. They are especially important to the field of healthcare since they enable measurement of important indicators of patient health such as electrolytes and glucose in blood. Continued development and improvements in electrochemical sensors can result in more accessible, affordable, and effective diagnoses and treatment strategies. Electrochemical sensors employ electrodes, usually modified with a recognition agent specific for the analyte (the biomolecule of interest). The presence of the analyte at the electrode surface is typically measured through an electrochemical reaction that generates a signal in the form of an electric current or difference in electric potential. As an alternative, electrochemiluminescence, a phenomenon whereby an electrochemical reaction generates a product in an electronically excited state that is capable of emitting light, has great benefits due to its high sensitivity, selectivity, and extremely low background signal. Here we employ a camera equipped with a complementary metal-oxide semiconductor (CMOS) detector that is interfaced with a simple zoom lens to measure ECL generated at low-cost pencil graphite electrodes and small electrode arrays using tris(2,2′- bipyridyl) dichlororuthenium(II) hexahydrate ([Ru(bpy)3]2+) with tri-n-propylamine (TPA) as the coreactant. ECL signals produced at pencil graphite working electrodes were linear with respect to [Ru(bpy)3]2+ concentrations for 45–450μM [Ru(bpy)3]2+. The detection limit was found to be 2µM using the CMOS camera with exposure time set at 10s. This proof-of-concept work suggests the pencil graphite electrode with simple imaging system platform can be applied for ECL-based biosensing strategies.

Physics-based electrochemical models are useful tools for optimizing battery cell and material design, managing battery use, and understanding physical phenomena, all of which are key in enabling adoption of batteries to electrify transportation, grid storage, and other high carbon emission industries. Fitting these models to experiments can be a useful approach to determine missing parameters that may be difficult to identify experimentally. In this dissertation, two use cases of this approach — model parameterization and degradation tracking — are explored. An introduction to the need for batteries and an overview of challenges in the field is presented in Chapter 1. Of these challenges, those that can be addressed by battery modeling solutions are discussed in further detail. An overview of continuum level physics-based electrochemical models is provided, and the case is made for the utility of parameter estimation. In Chapter 2, an extension of a published model for lithium trivandate cathodes for lithiumion batteries is outlined. While the original model described (de)lithiation and phase change in the cathode, the new model describes simultaneous lithiation of the original phase, lithiation of the newly formed phase, and phase change. Parameters associated with the thermodynamics and kinetics of charge transfer and lithium transport in the second phase are estimated directly from experimental data. This study serves as an example of using the model fitting approach to determine model parameters that would be difficult to isolate and measure experimentally. Chapter 3 explores a similar concept of model parameterization, this time focusing on the electrode tortuosity. Tortuosity is a hard to quantify parameter that describes how tortuous of a path lithium ions must travel through an electrode or separator. Because there are several experimental measurement techniques suggested in the literature that do not always provide consistent results, an approach to fit the tortuosity to a standard rate capability experiment is introduced. The Bayesian approach returns uncertainties in tortuosity estimates, which can be used to predict a range of outcomes for high-rate performance. Covariance between parameters in the model and their impact on uncertainties in tortuosity is also discussed. Beyond model parameterization, parameter estimation can also be useful in the context of tracking degradation by fitting a physics-based model over the course of cycling and interpreting the evolution of the parameter estimates. In Chapter 4, this idea is explored by fitting the model developed in Chapter 2 to cycling of an LVO cell. Parameter estimates are interpreted in conjunction with traditional tear down and electrochemical analysis to identify root causes of degradation for this cell. Depending on the number of parameters being simultaneously estimated, it can become an onerous task to fit model parameters, especially if the physics-based model cannot easily be enclosed in an efficient optimization algorithm. To this end, machine learning (ML) can be useful. If a ML model is trained offline on synthetic data generated by a battery model to map the observable electrochemical data to parameters in the battery model, the ML model can be deployed to estimate parameters from experiment. These models can be referred to as inverse ML models, since they perform the inverse task of a "forward" physics based model. The procedure described above is implemented in Chapter 5. Interpretable ML models are trained on published synthetic data generated by equivalent circuit models. Pseudo-OCV (slow charge, C/25) full cell voltage curves are passed into the inverse ML models to estimate degradation modes in lithium ion batteries and classify which electrode limits cell capacity. These models are useful in diagnosing the state of the battery at any given time. Accuracies of the inverse ML models are evaluated on independent test sets also composed of synthetic data and are published to benchmark future diagnostic studies. The insights derived from the trained ML models in terms of which features in the full cell voltage curves are predictive of the degradation modes are compared to expert insights. In chapter 6, the robustness of the inverse ML approach towards model-experiment disagreement is probed. If the experiment does not directly map onto the protocol used to generate the synthetic training data for the ML model, or if the model itself is inherently a poor descriptor of experiment, the inverse ML model will inevitably return inaccurate estimates. In this chapter, a feed forward neural network (NN) is employed as the inverse ML model. In two case studies of model-experiment disagreement, the NN returns biased parameter estimates. A simple data augmentation procedure is introduced to mitigate these biases. Chapter 7 ties together the understanding developed in the previous chapters by applying more robust neural networks to estimate parameters for LVO cells cycled at different rates. This study demonstrates how to interpret parameter estimates in conjunction with cycling data to gain mechanistic insight into degradation. A complex map of coupled degradation hypotheses is reduced to a smaller subset of possible mechanisms for two exemplary LVO cells, and parameter estimates for a larger set of LVO cells are discussed. The framework presented in this study synergistically combines experiment, physics-based modeling, and machine learning to better understand degradation phenomena.

Direct ethanol fuel cells are of interest due to the high energy density, ease of distribution and handling, and low toxicity of ethanol. Difficulties lie in finding a catalyst that can completely oxidize ethanol and resist poisoning by intermediate reaction species. Degradation of the catalyst layer over time is also an issue that needs to be addressed. In this work, niobium doped-titanium dioxide (Nb-TiO2) is investigated as a platinum (Pt) support due to its increased resistance to corrosion compared to the common catalyst support, carbon. It has also been seen in the literature that TiO2 is able to adsorb OH and assist in freeing Pt sites by further oxidizing COad to CO2 and thereby increasing the catalytic activity of catalysts toward ethanol oxidation. The TiO2 support is mixed with carbon, forming Nb-TiO2-C, in order to increase the conductivity throughout the support. The electrochemical activity and direct ethanol fuel cell (DEFC) performance of this novel catalyst is investigated and compared to that of two common catalysts, carbon supported Pt (Pt/C) and carbon supported platinum-tin (PtSn/C). While the conductivity of the Pt/Nb-TiO2-C electrodes was low compared to that of the carbon supported electrodes, the overall catalytic activity and performance of the TiO2 supported catalyst was comparable to that of the Pt/C catalyst based on the electrochemically active surface area. / Master of Science

A study of the electrochemistry of the PbS-H₂O and PbS-KEX-H₂O systems has been made by carrying out thermodynamic calculations, electrochemical experiments and microflotation tests. Particular attention has been paid to how well this system can be described by equilibrium thermodynamics. The thermodynamic calculations are more comprehensive than previous ones of this type since they are based on a mass balance which includes both insoluble and soluble species. The data they provide include equilibrium concentrations of all dissolved species at any E_h and pH and an E_h-pH stability diagram for each collector addition. Also, two- and three-dimensional plots showing the effect of E_h and pH on xanthate uptake by the galena surface have been presented for the first time. These are particularly useful because they can be directly compared to observed flotation data. The results of voltammetry, IGP and potential-step experiments suggest that the oxidation of galena at pH 6.8 and 9.2 begins at a potential below the value predicted by bulk thermodynamics with the electrosorption of OH⁻ and the formation of a metal-deficient sulfide and a surface lead oxide. When oxidation becomes extensive enough, bulk products, Sº and PbO, begin to nucleate. Thiosulfate is detected at pH 9.2, but only becomes significant at high potentials. The electrochemical experiments indicate that xanthate adsorbs onto galena via a one-electron transfer chemisorption reaction in the first monolayer and via the formation of PbX₂ in subsequent layers. It also appears that galena oxidation and xanthate adsorption are competitive processes that tend to inhibit each other. Ground galena exhibits natural floatability at pH 9.2 as long as oxidation extends to the formation of a metal-deficient sulfide, but not to bulk PbO. When 10⁻⁵ M xanthate is added, the upper potential limit for flotation agrees well with the value predicted from thermodynamics for the decomposition of PbX₂. The lower limit, on the other hand, is at least 200 mv lower than any of the predicted values. PbS dissolves anodically at pH 1.1 and 4.6 to form Pb²⁺ and Sº first by a random surface process and then by a nucleation and growth mechanism once oxidation becomes extensive enough. At pH 0, the relation between the open-circuit potential and mineral solubility, as predicted by the thermodynamic calculations, agrees quantitatively with that determined experimentally. However, as the pH is increased to 1.1 and 4.6, the system becomes increasingly less reversible. / Ph. D.

Determination of bio-material by using enzyme, fluorophore or metal-nanoparticles as markers is very important. Generally, gold-nanoparticles have been used frequently as marker for increasing the sensitivity in bio-chemical assay. In this research, gold-nanoparticles were used as marker for immunoassay, DNA sequence assay, and protein analysis. However, the size of gold-nanoparticles affects directly the results of electrochemical detection. For improving the sensitivity of electrochemical method, enlargement of gold-nanoparticles was used in this study. By electroless deposition, Au will be deposited on the surface of gold-nanoparticles. The electrochemical response will thus be increased substantially. In immunoassay and DNA sequence assay, traditional 96-wells microtiter plate was used for immobilizing antibody or oligonucleotide, and the gold-nanoparticles were marked subsequently base on the immunoreaction or protein reaction of streptavidin and biotin. After gold-nanoparticles were enlarged, they were dissolved and transferred to an electrochemical cell for square wave stripping voltammetry¡]SWSV¡^analysis. Under optimal experimental condition, dynamic range of 1 ~ 500 pg/mL and 0.52 ~ 1300 aM were found respectively for RIgG and Target DNA analysis, and a good linear relationship¡]R2 = 0.9975 and 0.9982¡^. The relative standard deviation¡]R.S.D.¡^ of blank were 2.8 % and 2.4 %¡]n = 11¡^for immunoassay and DNA assay, respectively. And the variance was 2.4 %¡]n = 9¡^and 2.4 %¡]n = 12¡^for immunoassay and DNA assay, respectively. The detection limit¡]based on S/N = 3¡^of RIgG and DNA were 0.25 pg/mL and 0.52 aM, respectively. They are very competitive compared with similar results reported in the literature. Additional, a gold nanoelectrode ensemble¡]GNEE¡^coupled microchip system was developed for bio-electrochemical analysis. Due to the difference in mobility of urea and urease were mixed and allowed the enzymatic reaction to proceed in microchannel. The enzymatic product NH4+ was determined by the coupled GNEE at the outlet of the channel. Another experiment of streptavidin conjugated gold-nanoparticles¡]streptavidin-Au¡^, reductant and gold-ion¡]Au3+¡^solution was be applied here, too. The product, NH4+ or Au3+ was passed through downstream of microchannel and detected by GNEE of electrochemical system. Satisfactory linear relationship¡]R2 = 0.9778 and 0.9657¡^were found from 0.1 mM to 50 mM for NH4+ and urea in the range of 0.02 mM to 5.0 mM, respectively. The other satisfactory linear relationship¡]R2 = 0.9842 and 0.9507¡^ were found between 3.75 mg/mL and 3.75 g/mL for Au3+ and streptavidin-Au in the range of 0.2 ng/mL to 100 ng/mL, respectively. Variances of 2.5 %¡]n = 6¡^was found for analysis of with the microchip system.

Thesis (M.S.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.