Browsing by Subject "Chemiluminescence"
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Item Electrochemistry and electrogenerated chemiluminescence of semiconductor nanoparticles(2005) Bae, Yoonjung; Bard, Allen J.Electrochemical band gaps from semiconductor nanoparticles (NPs) such as CdSe and CdTe showed a size-confinement effect, and the values were in good agreement with the optical band gaps. For example, differential pulse voltammetry of 2.8 nm and 3.5 nm CdSe NPs showed electrochemical band gaps of 2.41 and 2.17 eV from the peak-to-peak separations. A large anodic wave from both CdSe and CdTe NPs was explained by the electrochemical oxidation of the particle surface of trioctylphosphine (TOP)-Se and TOP-Te species. Electrogenerated chemiluminescence (ECL)-potential curves also showed unique electronic properties of NPs. In general, ECL of NPs was sensitive to surface energy states. In the case of CdSe NPs, ECL onsets at positive potentials vii were suggested to result from electron transfer at hole traps in the NPs. The 2.0, 3.0, and 4.8 nm CdSe NPs showed size-dependent ECL behavior. The smallest particle, 2.0 nm, showed that most of the ECL signal came from the surface states, and surface state-ECL was observed at a wavelength that was red-shifted 200 nm from the band edge position. The ratio of surface state to band edge-ECL intensity was lower for larger particles and for densely-packed NP films. The surface stateECL was negligible at red-emitting CdSe and CdTe NPs due to changes in the luminescent surface states during the growth of the particles. Red-emitting Si NPs also showed ECL in good agreement with the photoluminescence (PL). CdSe/ZnSe core/shell NPs and oxygen-treated CdSe NPs showed a similar enhancement of PL intensity through the surface treatment. However, in the ECL measurements, oxygen treatment of the NPs decreased the surface state-ECL intensity with almost no change in the band edge-ECL, whereas the CdSe/ZnSe core/shell system increased the intensity of band edge-ECL. The ZnSe shell, with its wider band gap, can facilitate electron transfer from the surface energy states to the core of particle, which can not be expected in the oxygen-treated particle. ECL studies of the surface modified NPs demonstrate that ECL is an effective way to investigate the surface states of NPs.Item Electrochemisty and electrogenerated chemiluminescence of Ru(phen)₂dppz(BF₄)₂ both free and intercalated into DNA(2007-05) Calhoun, Robert Lee; Bard, Allen J.Ruthenium (II) bisphenanthroline dipyridophenazine, Ru(phen)2dppz2+, exhibits first oxidation and reduction voltammetric responses which correlate well with the UVvis spectroscopy and are typical to the compound class. The complex proves energy sufficient for electrogenerated chemiluminescence (ECL), and does so in aqueous media with co-reactants, also similar to its phenanthroline and bipyridine analogues. However, this behavior is curious since this compound’s aqueous photoluminescence (PL) is undetectable but exhibits ‘light switch’ behavior upon intercalation into both calf thymus DNA and other polynucleotides in that the PL greatly increases. The ECL of both the free and intercalated complex is presented as well as scanning electrochemical microscopy (SECM) studies to understand the complex’s kinetic behavior in water upon oxidation. In an effort to understand the SECM results, the program COMSOL Multiphysics is used to model the EC’ (catalytic) following reaction. The simulation results are validated using the ferrocyanide/cysteine system, which is known to exhibit the EC’ mechanism.Item Electrogenerated chemiluminescence of 9,10-substituted Benzo(k)fluoranthenes and of surface bound Ru(bpy)₃²⁺ on platinum silicide(2001-12) Fabrizio, Eve Frances; Bard, Allen J.Three aspects of electrogenerated chemiluminescence (ECL) were studied. First, the effect of substitution on the photochemical, electrochemical and ECL properties of 7,12-diphenylbenzo[k]fluoranthene was investigated. Upon the addition of methyl groups, both of which are weak electron donors, and the subsequent addition of sulfone, an electron withdrawing group, onto the 9,10 positions of 7,12-diphenylbenzo[k]fluoranthene, only small changes in the photophysical and electrochemical properties were observed. This was not the case for the rate of radical cation-radical cation coupling or dimerization, which occurs during the electrochemical oxidation of these compounds. Upon addition of the electron donating methyl groups, the rate decreased to 195 M -1 while the addition of the electron withdrawing sulfone group increased the rate to 20,000 M -1 . As a result, the amount of dimer emission that was observed in the ECL spectrum of these two benzo[k]fluoranthene derivatives correlated directly with these rates. Second, by using these differences in the rate of dimerization, one reaction that is responsible for the formation of the emitting excited state upon electrochemical reduction of polycyclic aromatic hydrocarbons in the presence of the ECL coreactant, peroxydisulfate, was determined. Specifically, the formation of the radical cation through the homogeneous oxidation of the neutral hydrocarbon by sulfate radical anions was confirmed by emission from the dimer during electrochemical reduction in the presence of this coreactant. Therefore, emission under these electrochemical conditions most likely occurs through a radical ion annihilation reaction between the electrochemically generated radical anion and the chemically generated radical cation. Finally, platinum silicide (PtSi) was evaluated as a potential platform for ECL based assays. Through cyclic voltammetry and scanning electrochemical microscopy (SECM), the oxide layer on PtSi, which was shown to be stable upon extensive potential cycling, did not interfere with heterogeneous rate of electrochemical oxidation of the ECL label, Ru(bpy)3 2+. Upon modifying the oxidized PtSi surface with an aminosilane, Ru(bpy)3 2+, either directly or as a label bound to DNA, was chemically attached to the surface. In both cases, ECL of this bound label was detected showing the viability of using this surface as a platform for chemical and biological assays involving ECL detection.Item Electrogenerated chemiluminescence of phenylquinoline-phenothiazine donor-acceptor molecules, dipyrromethene-BF₂ laser dyes and bent-pyrene-containing cyclophanes(2003-12) Lai, Rebecca Yun Kay, 1977-; Bard, Allen J.Four aspects of electrogenerated chemiluminescence were studied. First, the effect of molecular geometry on the photophysical, electrochemical and ECL properties of 3,7-[bis[4-phenyl-2-quinolyl]]-10-methylphenolthiazine and 7,7'-bis-(6-hexyl-4 phenylquinolin-2-yl)-10,10'-dimethyl-10H,10H'-[3,3']biphenothiazinyl were investigated. Upon addition of phenylquinoline groups onto the phenothiazine rings, apparent changes in the photophysical and electrochemical properties were observed. The optimized geometry showed that the phenylquinoline moieties were twisted from the phenothiazine rings, thus inhibiting any delocalization of the charge upon electrochemical oxidation or reduction. This geometry allows the production of stable radical ions needed to generate ECL from phenothiazine within the potential window. Second, the effect of chemical structures on the photophysical, electrochemical and ECL properties of four novel pyrenophanes were studied. When compared to pyrene, these compounds displayed a shift in the thermodynamic reduction potentials to more negative values. AM1 calculations also showed that the LUMO energy increased with the degree of nonplanarity. Similar to pyrene, their ECL spectra showed broad “excimer like” emission in addition to the monomer emission. Similar studies were performed on five boron-based laser dyes with different substituents or degree of substitution. High fluorescence quantum yields were obtained for all dyes except PM 597. Moderately intense ECL was observed from PM 567, PM 580, and PM 597, compounds that exhibited reversible electrochemical oxidation and reduction. The third aspect involved the study of polycyclic aromatic hydrocarbons in presence of tri-n-propylamine (TPrA) in MeCN/benzene solutions. ECL was observed from three out of the eight compounds studied. Based on the energetic criterion for ECL, the potential for oxidation of the intermediate free radical was found to be about -1.7 V vs SCE. By studying the fluorescence quenching of several PAHs by TPrA, the standard potential for oxidation of TPrA was estimated as 0.9 V vs SCE. The last aspect involved the study of ECL energy transfer and eventually utilized the self-quenching capability of PM 567 to determine the self-association constant (Ka) for dimeric oligo(aminotriazine) in a mixed solvent system. Analyzing changes observed in the ECL intensity with respect to the concentration of PM 567-labeled oligomers yielded a dissociation constant (Kd) of about 1.4 x 10-3 M (Ka = 7.1 x 102 M-1), a value slightly higher than the literature value.Item The electrogenerated chemiluminescence of unique organic chromophores(2007-12) Sartin, Matthew McCullough, 1982-; Bard, Allen J.Electrogenerated chemiluminescence (ECL) studies were performed on several interesting compounds. A series of silole-based (silacyclopentadiene) chromophores was examined to understand the effects of their structure on the electrochemistry and spectroscopy of these compounds. A case was observed in which high steric hindrance improved ECL by inhibiting internal conversion and protecting radicals from secondary reactions. Another case was observed in which steric effects induced a rotation in the silole substituents, increasing secondary reactions and lowering quantum efficiency ([Phi subscript PL]). Spiro-FPA, which consists of two DPA centers, exhibits excimer formation despite high steric hindrance, due to its ability to form di-ions, which have a greater electrostatic attraction to one another than mono-ions. The compound (dppy)BTPA is a highly solvatochromic, boron-containing chromophore that was examined in a variety of solvents. Of note is the emission in pure acetonitrile, which is prominent in the ECL spectrum, but barely visible in the photoluminescence. Finally, B⁸ amide, a compound based on the laser dye, BODIPY, was examined. It exhibited unusual ECL characteristics. These include a strong, long-wavelength emission and transients that are clearly visible for 20 min or more, but display dramatically varying light intensities with each pulse. Evidence for the contribution of a film formed with the oxidation product is presented. Additionally, ECL simulations are performed using a general physics software package to better understand some of the observed phenomena.Item Electrogenerated chemiluminescence with amine and benzoyl peroxide coreactants: reactivity and reaction mechanism studies(2003) Choi, Jai-pil; Bard, Allen J.The electrogenerated chemiluminescence (ECL) of tris(2,2′- bipyridine)ruthenium(II), Ru(bpy)3 2+, was investigated using amine coreactants. When amine coreactants were oxidized, they produced both sufficiently strong reducing (R2NC• HR′) and oxidizing (R2N•+ CH2R′) agents and these agents were relatively stable to diffuse and react with Ru(bpy)3 2+ or electrochemically generated Ru(bpy)3 3+ to generate Ru(bpy)3 2+*. Most amine coreactants produced two ECL waves in a plot of ECL vs electrode potentials: the first occurred before the oxidation of Ru(bpy)3 2+ and the second occurred immediately after the oxidation of Ru(bpy)3 2+, implying two different ECL mechanisms participate in the first and second ECL, except for N, N, N′, N′-tetra-n-propylmethane diamine and N, N, N′, N′-tetra-n-propylethylene diamine. ECL produced by monoamine coreactants gave stronger emissions than diamines, and acyclic amines produced stronger ECL than heteroalicyclic amines. The ECL intensity increased as the number of carbon atoms increased in the same group of amines except for those with the piperazine group. Tri-n-propylamine produced the most intense first and second ECL. Benzoyl peroxide (BPO) was studied as a new coreactant for neutral red (NR), ter(9,9-diarylfluorene)s (TDAFs) and Ru(bpy)3 2+. When BPO was reduced, it produced the strong oxidizing agent, C6H5CO2 • via an ECE process. Then electrochemically reduced NR•−, TDAF•−, or Ru(bpy)3 + reacted with C6H5CO2 • to produce ECL. At a high concentration of BPO (e.g. > 10 mM compared to 0.5 mM NR), ECL quenching by BPO was significant, as confirmed by fluorescence quenching experiments. NR could be used as both a pH indicator and ECL emitter in acetonitrile. A yellow-to-red color change was observed when a NR solution was titrated with acids. The protonated form of NR (NRH+ ) did not produce ECL due to two-electron reduction of NRH+ and lack of sufficient energy for the ECL reaction. However, NR generated ECL emission of 610 nm. TDAFs emitted at ∼ 400 nm (blue ECL). In annihilation ECL, significant emission of TDAF excimers, mainly formed by coulombic interactions when radical cations were annihilated by radical anions, interfered with their blue emission (φECL ≤ 0.05 %) Excimers were not observed in fluorescence. No significant excimer emission was found when BPO coreactant was used.Item Studies of applying supramolecular chemistry to analytical chemistry(2008-12) Hewage, Himali Sudarshani, 1971-; Anslyn, Eric V., 1960-Supramolecular chemists can be thought of as architects, who combine individual non-covalently bonded molecular building blocks, designed to be held together by intermolecular forces to create functional architectures. Perhaps the most important assets of a supramolecular chemist, however, are imagination and creativity, which have given rise to a wide range of beautiful and functional systems. For years, analytical chemistry has taken advantage of supramolecular assemblies in the development of new analytical methods. The role of synthetic supramolecular chemistry has proven to be a key component in this multidisciplinary research. As such, the demand for synthetic receptors is rapidly increasing within the analytical sciences. The field “supramolecular analytical chemistry” involves analytical applications of synthetic organic and inorganic chemical structures that display molecular recognition properties and self-assembly but also signal these events. Chapter 1 presents an introduction to the background literature relevant to the central themes of the research presented in this thesis. The nonthermal production of visible light by a chemical reaction leads to the term “cool light”, and the process is called chemiluminescence. Although chemiluminescent reactions are not rare, the production of “cool light” holds such fascination for both chemists and nonchemists that demonstrations of chemiluminescent reactions are always well received. A glow assay technology for the detection of a chemical warfare simulant is presented in Chapter 2, which is based on modulating the peroxyoxalate chemiluminescence pathway by way of utilizing an oximate super nucleophile that gives an off-on glow response. As an alternative to highly analyte-specific synthetic receptors, trends in chemical sensing have shifted to the design of new materials and devices that rely on a series of chemo- or biosensors. The research relevant to Chapter 3 focuses on investigating the use of a single receptor, for sensing two different analytes; thiols and metal ions, utilizing a squaraine as the receptor in a sensor array format. The data is interpreted with principal component analysis. Finally Chapter 4 discusses an attempt to design and synthesize a chemosensor based on the luminophore-spacer-receptor format by incorporating the two concepts photoinduced electron transfer and peroxyoxalate chemiluminescence.