Luminescence decay curves from one dimensional mixed crystals of CsMn$\sb{\rm x}$ (Mg or Cd)$\sb{\rm 1-x}$Br$\sb3$ with small fraction of Mn (x = 0.02 $\sim$ 0.3) have been analyzed to gain insight into the energy migration. As the temperature is raised, exciton migration between pairs and single ions is observed. Information about exciton migration process between pairs and single ions was obtained by analyzing the kinetics of decay curves obtained at different excitation wavelength. By varying the concentration of Mn$\sp{2+}$ ions, it is possible to determine the critical limit for exciton migration in lattice. Luminescence decays of (CH$\sb3$)$\sb4$NMnCl$\sb3$ doped with Cu$\sp{2+}$ and/or Cd$\sp{2+}$ were measured at various temperatures. By using the HRM model to simulate data, detailed insight into the rates and energy barriers of the different exciton migration processes were obtained The luminescence studies on dimeric d$\sp8$-d$\sp8$ complex K$\sb{4}\{$Pt$\sb2$(PCP)$\sb4\}\cdot$6H$\sb2$O (PCP = $\mu$-P,P,-HO(O)PCH$\sb2$P(O)OH$\sp{2-}$) have been conducted. At room temperature in aqueous solution, the $\sp3$A$\sb{\rm 2u}$ excited state of Pt$\sb2$(PCP)$\sb4\sp{4-}$ has a lifetime of only 0.055 $\mu$s. Measurements of the lifetimes of the excited states of Pt$\sb2$(PCP)$\sb4\sp{4-}$ at various pH and solvent viscosity values were carried out. Small shifts in absorption and emission maxima were observed between the solid and fluid solutions. The activation energy for the nonradiative decay is 1200 $\pm$ 100 cm$\sp{-1}$. The short lifetime of $\sp3$A$\sb{\rm 2u}$ state in solution is likely due to the presence of a manifold of twisted excited state rotamers. The phosphorescent lifetime of the compound shows a temperature dependence that is consistent with a zero field splitting of 39 cm$\sp{-1}$ in the triplet manifold of excited states The unique dimeric Rh complex $\{$Rh$\sb2$(PNP)$\sb4\}$((C$\sb6$H$\sb5$)$\sb4$B)$\sb2$ (PNP = CH$\sb3$N(P(OCH$\sb3$)$\sb2$)$\sb2$) is rather flexible and adopts a number of distinct conformational forms in solid state. Luminescence spectra and emission dynamics of two crystalline forms of the complex show a dramatic temperature dependence which is consistent with a thermally activated structural transformation of the phosphorescent excited state The X-ray diffraction data of the d$\sp8$-d$\sp6$ complexes MM$\sp\prime$D$\sb2$(CO)$\sb4$Cl where M = Rh(I) or Ir(I) and M$\sp\prime$ = Mo(0) or W(0), D = bidentate ligand (CH$\sb3$NP(OC$\sb3$H$\sb7$)$\sb2$)$\sb2$ indicated the presence of a metal-metal bond. The absorption and emission spectra were used to assign the electronic structure. Luminescence lifetimes for this novel type of d$\sp8$-d$\sp6$ dimer were also obtained / acase@tulane.edu

Nonthermal plasma (NTP) methods present potential advantages in the treatment of dilute volatile organic compounds (VOCs) as well as NOx in exhaust effluents, with relatively low energy consumption. Efforts have been under way since at least the early 1990s to improve practical techniques via a better fundamental understanding of NTP phenomena. Mechanistic understanding of the early post discharge chemistry is fundamental to characterizing and then improving NTP remediation for various VOCs. However, direct study of post discharge chemistry has been limited, leading to a growing demand for general capabilities to identify numerous post discharge species, stable and reactive, neutral and ionic. Molecular beam methods afford this possibility. Indeed, vuv and resonant photoionization methods already are established in environmental compound trace detection. In order to study NPT remediation chemistry of alkylbenzenes, we first looked at post discharge products of toluene and other alkylbenzenes seeded in He, then co-added additional species, O2 in particular. Now employing ∼800 nm fs pulses for photoionization, we have extended our studies to additional alkylbenzenes as well as to pyridine. The newly obtained data reveal important information about the intermediate species in benzene, toluene and other alkylbenzene species following corona discharges. As established from discharge, flame, and pyrolysis product studies on benzene in rare gases, the product chemistry shows general similarities in each case, in particular the formation of higher mass polycyclic aromatic hydrocarbons (PAHs). The vuv and fs laser photoionization time-of-flight mass spectrometry combined with molecular beam technique have proven to be ideal and sensitive tools for a comprehensive diagnosis of product formation in plasma chemistry / acase@tulane.edu

No description available.

Ultrathin organized films of organic electronic materials, such as phthalocyanines (Pc), are promising for both fundamental and applied studies due to their special optical, electronic and photoconductive properties. The studies presented in this dissertation include fabrication of ultrathin molecular assemblies by molecular beam epitaxy and Langmuir-Blodgett techniques. The degree of molecular order, extent of charge transfer and the morphology within these films, assessed by methodologies, such as photoelectrochemistry, electrochemistry, surface analysis and optical spectroscopy were discussed and characterized. Under high vacuum condition, a wide range of ordered structures of some trivalent metal phthalocyanines, such as GaPc-Cl, InPc-Cl and AlPc-F, can be fabricated. These materials exhibit "layer-by-layer" growth on the single crystal SnS₂ surface when deposited by molecular beam epitaxy (MBE). The MBE technique allows for closer packing of these highly ordered phthalocyanines than in self-assembled (SA) or Langmuir-Blodgett (LB) thin films, due to the lack of hydrocarbon side chains which are necessary for control of molecular architecture during SA or LB depositions. Several new solution processable substituted phthalocyanines are introduced, which due to their strong self-assembled tendency, may be suitable for the formation of well organized thin films by SA and LB techniques. It is found that the types of the substituents attached to the Pc rings play a significant role in determining both the aggregation tendency and the electrochemical properties of Pcs. Surface pressure-area isotherms of these substituted phthalocyanines show that there can be one or two stable phase transition regimes for monomolecular film at the air/water interface. On-trough spectroscopic studies of benzylalkoxy substituted phthalocyanines show that in the pressure-area region prior to the formation of the first stable phase extensive aggregation has occurred. Electrochemical studies of fully compressed films of substituted phthalocyanines on certain substrates show the presence of multiple electroactive domains, controlling the oxidation or reduction process of the Pc rings. Spectroelectrochemical studies of LB films of CuPcOC₂OBz suggest that the presence of both monomer and aggregates leads to the two separate oxidation processes.

Applications of planar integrated optical waveguide (IOW) technology to problems in surface spectroscopy and optical chemical sensing have been partly limited by the difficulty of producing high quality glass IOWs is. The fabrication of IOWs by the sol-gel method from methyltriethoxysilane and titanium tetrabutoxide precursors has therefore been developed. The physical, chemical, and optical properties of the films were studied using a variety of analytical techniques. The results show that the catalyst used to accelerate the sol-gel reaction strongly influenced the optical quality of the IOW. A novel optical sensing platform was subsequently developed using a sol-gel derived, laminate planar IOW structure. The sensing element is fabricated by coating a sol-gel IOW with a second, porous sol-gel layer in which optical indicator molecules are physically entrapped, yet remain sterically accessible to analytes that diffuse into the pore network. Formation of a complex between the analyte and entrapped indicator is detected via attenuated total reflection (ATR) of light guided in the IOW. Feasibility was evaluated by constructing IOW-ATR sensors for Pb2+ and pH, based on entrapped xylenol orange and bromocresol purple respectively. The response of both sensors was sensitive and rapid. This work was further extended to the development of a new class of gaseous iodine sensors. The sensing principle is based on the detection of a charge transfer complex formed between iodine and phenyl groups that have been incorporated into a porous, methylated glass film. The sol-gel iodine sensor exhibits a linear response to gaseous I2 in the range of 100 ppb to 15 ppm with response and recovery times less than 15 sec. Langmuir-Blodgett (LB) films have also been deposited on a sol-gel IOW from zinc 1,4,8,11,15,18,22,25-octabutoxy-phthalocyanine (ZnPc). Planar waveguide linear dichroism was used to determine molecular orientation in a ZnPc LB monolayer. The IOW-supported ZnPc monolayer was found to exhibit a sensitive spectral response to gaseous I2. The overall optical sensing approach described in this dissertation is technically simple, inexpensive, and applicable to a wide variety of chemical sensing problems.

Recent intervention trials reported that smokers given dietary β-carotene supplementation were at increased risk of lung cancer and overall mortality. These results were unexpected based on previous observational epidemiology, which suggested β-carotene would decrease the onset of lung cancer in these individuals. The mechanism by which β-carotene supplementation results in increased lung cancer among smokers has yet to be defined. However, one proposed explanation is that β-carotene acts as a prooxidant in lungs exposed to cigarette smoke and exacerbates oxidative damage. This project has examined the consequences resulting from interactions of cigarette smoke with β-carotene in model systems. A novel β-carotene oxidation product, 4-nitro-β-carotene has been identified from smoke oxidation of beta-carotene in solution. This product has been isolated by both reverse-phase and cyano-column HPLC, and characterized by UV-vis spectroscopy, APCI-LC-MS, and NMR spectrometry. This class of products includes cis and all-trans isomers of 4-nitro-β-carotene. A new method for measuring primary products of lipid peroxidation has been developed. This method is specific and sensitive for the determination of 9- and 13-hydroxy fatty acid methyl esters of octadecadienoic acid as pentafluorobenzoyl esters by GC-ECD. These compounds are derived from the first stable products of linoleic acid oxidation. Using the method discussed above, the interactions between β-carotene and cigarette smoke were examined in a liposomal model system. DLPC liposomes showed little differences in oxidative damage with or without β-carotene incorporation. This result was consistent with gas-phase or whole smoke exposures. The effect of β-carotene on the oxidation of other antioxidants was also examined. Both the lipid soluble antioxidant α-tocopherol and the water soluble antioxidant ascorbate showed lower oxidation rates due to smoke exposure in the presence of β-carotene than without. These data indicate that β-carotene does not have prooxidant effects in this system. β-carotene is oxidized by cigarette smoke in model systems. 4-Nitro-β-carotene is one of several classes of products resulting from cigarette smoke oxidation of β-carotene. β-Carotene incorporation did not increase oxidation of lipid or other antioxidants upon smoke exposure. It is unlikely a prooxidant effect of β-carotene is responsible for increased lung cancer observed in recent intervention trials.

A study for non-destructive measurement and analysis of agricultural products was undertaken. Some enhancements were made to a spectrophotometer, DK-2A to meet the requirements of low uniform error band when using the factor analysis method. The instrument was modified by adding an integrating sphere, optical transducer, and electronic interface linked to a computer. The instrument was calibrated using targets traceable to NITS standards of BaSO₄ with mixtures of Carbon Black. This gave a range of known reflectance and provided consistent and reproducible data every 5 nm wavelengths between 350 nm and 800 nm. The spectral wavelength bands of the different biological materials were studied with target factor analysis. Target factors were applied in biological materials to characterize the important spectral properties. Pigment of foods, chlorophyll, carotenoid and myoglobin were separated from the spectral response of oranges, apples and meat. Their respective spectral signatures were determined.

<p> To promote its use in nutraceutical and functional food ingredients, jiaogulan (<i>Gynostemma pentaphyllium</i>) of different sources, genotypes and parts of the plant were investigated for their chemical profiles and biological properties. The first part of this research studied five commercial jiaogulan for their phytochemical profiles, and antioxidant, anti-proliferative and anti-inflammatory effects. It was found that individual jiaogulan samples significantly differed in their chemical and biological properties. The second part of this research further investigated phytochemical compositions and biological activities in different genotypes and parts of jiaogulan. The results indicated that different genotypes or plant parts of jiaogulan may have different biological activities. The results led to the third study to develop chromatographic fingerprinting techniques for differentiating genotypes and plant parts of jiaogulan using LC/MS. LC-MS fingerprints combined with PCA were able to differentiate diploid and tetraploid, and the leaf and whole botanical jiaogulan. The results from this research suggest the potential use of selected jiaogulan to improve human health while enhancing food agriculture economy, and indicate that HPLC fingerprinting may be a useful controlling the quality of jiaogulan.</p>

Design, development, and application of novel all-solid-state spectroscopic gas sensors is reported. These compact instruments employ mid-infrared difference-frequency generation pumped by room-temperature semiconductor lasers, and are capable of real-time selective measurement of trace gases in ambient air with better than 1 ppb precision (part per billion, by mole fraction). Their features and performance in the laboratory and field environment are examined and compared to that of traditional spectroscopic sensors.

Environmental and industrial systems have been investigated using vibrational spectroscopy. These applications were chosen to demonstrate the potential of vibrational spectroscopy as a means of obtaining molecular information from either in-situ or model environments in a rapid, convenient manner requiring minimal sample handling. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been used to investigated two systems in the area of environmental chemistry. Using the characteristic CO stretching bands of the Mn(CO)$ sb3$ fragment, methylcyclopentadienyl manganese tricarbonyl (MMT), an additive to Canadian gasoline, was detected on soils treated with gasoline up to twelve months after exposure. Its longevity on and its interaction with different soils and various substrates was studied. A breakdown of the local symmetry of the manganese tricarbonly moiety suggests a Bronsted-type interaction between the soil and the carbonyl ligands of MMT. The uptake by harbour sediments of two tributyltin species used as marine antifouling agents, was also studied using DRIFTS. Water/sediments ratios and salinity were investigated as factors affecting adsorption. A novel infrared cell for probing the gas-phase infrared spectroscopy (HAGIS) cell was used to study the thermal decomposition products of ethylxanthanate-treated sulphide minerals and those of the related ethylxanthate metal complexes. The gas-phase decomposition products from sulphide minerals treated with ethylxante include $ rm CS sb2, COS, CO sb2, CH sb4, SO sb2,$ ethanol and possibly metal xanthates. The relative amounts of the products depend on the type of mineral surface, the temperature and the atmosphere in the cell. Iron, zinc, lead, nickel and copper ethylxanthate complexes were synthesized, and their thermal decomposition products were also studied by HAGIS. The complexes were classified according to the generation of the primary gas-phase decomposition products. Schemes for the produ