1. 2-[2-(2vinylphenyl)ethenyl]thiophene ( 30 ) and 2,2-(o-phenylenedivinylene)dithiophene ( 31 ) were studied under pyrolytic and photolytic conditions, photolytic of 30 gave upon bicyclic product 35, whereas photolytic of 31 gave products 37 and 39, FVP of 30 and 31 gave 34 and 37, respectively,which all include naphthalene nucleus. 2. 2-methoxystilbene ( 17 ) and 3-methoxystilbene ( 18 ) were studied under pyrolytic conditions, FVP of 17 gave single product 2-Phenylbenzo[b]furan ( 23 ), FVP of 18 gave 2-phenanthrol ( 27 ), ( 4-phenanthrol ) ( 28 ), trans-3- hydroxystilbene ( 29 ), Fluoren 9 -one ( 30 ) and a pair of isomer 1H-benz[e]indene ( 11a ) and 3H-benz[e]indene (11b).

The aim of this study is to investigate and reveal challenges in photocatalytic CO2 reduction tests performed in liquid media. Effect of test conditions in photocatalytic studies are often underestimated with an assumption of negligible mass transfer limitations in observed rate results. In this study, effect of mass transfer limitations in liquid phase photocatalytic tests was revealed with stirring rate and gas hold-up time experiments performed with Pt/TiO2 and Cu/TiO2 catalysts. In addition, apparent activation energies of 12 and 19.5 kJ/mol found with Pt/TiO2 and Cu/TiO2 catalysts respectively indicate diffusion limitations which favor back oxidation reactions resulting in low reduction yields. Photocatalytic CO2 reduction reaction is named as Artificial Photosynthesis even though present artificial system does not have sophisticated transport and membrane systems which natural systems have. Similarities and differences between artificial and natural photosynthesis are studied in order to present ideas to improve present photocatalytic rates. Kinetic and microkinetic modeling of catalytic methanol production from CO2 hydrogenation on Cu surfaces were performed in order to have an idea about kinetic limitations at photocatalytic systems. Calculations were performed at temperatures and pressures at which photocatalytic studies are conducted. The results indicated that water has an inhibitory effect on methanol formation rates and higher pressures could be implemented in photocatalytic systems for higher rates. Another implication drawn from degree of rate control calculations is that H formation step plays an important role underlying the importance of water splitting in CO2 reduction reactions.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 263-285).

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : 48-51).

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, August 2001. / Includes bibliographical references. Also available on the Internet.

Dissolved organic matter (DOM) is crucial to carbon and nutrient biogeochemical cycling in the marine environment because it helps fuel heterotrophic microbial activity by providing substrates for degradation and remineralization. This study shows that substantial production of DOM in Texas estuaries can result from the solar radiation-enhanced dissolution (photodissolution) of particulate organic matter (POM). Experimental results showed that 0.4-6.6 mg C L⁻¹gsed⁻¹ of dissolved organic carbon (DOC) and 0.03-0.93 mg N L⁻¹gsed⁻¹ of total dissolved nitrogen (TDN) can be produced from irradiated sediment suspensions within 24 hours, and further that photodissolution may augment DOC and TDN loads in Texas estuarine waters by as much as 3-85% and 4-75%, respectively. Photodissolution can also enhance the optical thickness of the water column via the release of chromophoric dissolved organic matter (CDOM), which may subsequently further enhance photochemical processes in surrounding waters. Photoproduced CDOM appears to be of relatively high molecular weight and dominantly exhibits humic-like fluorescence, suggesting that photodissolution primarily occurs for humic moieties. Photodissolution was also observed for sterilized sediment suspensions, indicating that photochemical degradation of POM is the primary pathway of DOM production during photodissolution, as opposed to microbial mediated degradation or stimulation of benthic primary production by benthic phytoplankton or algae. Environmental and mechanistic factors controlling the extent of photodissolution in Texas estuaries may include sediment desiccation, water organic content, and sediment characteristics (organic content and lability of POM). Desiccated-rewetted sediments suspended in artificial seawater under solar irradiation produced ~40% more DOC and TDN than wet sediments, indicating the sediment dry-wet cycle may alter the 3-D structure of sediment grain matrices and thus might be a major controlling factor of photodissolution in salt marsh systems. The organic content of water used in sediment suspensions did not significantly influence DOC or TDN photoproduction by itself, but the combined influence of water organic content and sediment dry-rewet event played a substantial role in controlling the extent of photodissolution. In contrast to the results in artificial seawater, wet sediments produced slightly more DOC ([Delta]DOC=0.10 mg C gsed⁻¹) and substantially more TDN ([Delta]TDN=0.14 mg N gsed⁻¹) than dry-rewetted sediments in organic-rich Nueces Marsh water during 24 hours of photoincubation. Photodissolution dominantly produced humic-like DOM even though biologically labile organic matter was available in sediments, indicating that photochemical reactions preferentially occur with humic-like rather than protein-like organic matter. DOC and TDN production during photodissolution was strongly proportional to the amount of POC in sediment suspensions. On average, 69.2 ± 11.0 mg C of DOC and 9 ± 3.1 mg N of TDN was produced from 1 g of organic carbon in sediment suspensions after 24 hours of photodissolution. / text

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy was used in this thesis to study the photoreduction reactions and the photochemistry of chloro-substituted benzophenone (ClBP) triplets. The 3-chlorobenzophenone (3-ClBP), 4-chlorobenzophenone (4-ClBP) and 4,4′-dichlorobenzophenone (4,4′-diClBP) triplets exhibit similar properties to the parent BP triplet. In isopropyl alcohol (IPA), the hydrogen abstraction reactions were observed for the 3-ClBP, 4-ClBP and 4,4′-diDlBP triplets. The diphenylketyl (DPK) radicals produced from the hydrogen abstraction reactions were observed and the recombination of the DPK and dimethylketyl radicals at the para-position was observed to form a light absorption transient (LAT) species. In MeCN:H2O/1:1 aqueous solutions, these DPK radicals were also observed but with a slower formation rate and the LAT species was produced by reaction with OH radicals. Density functional theory (DFT) calculations were employed to help identify the intermediates seen in the TR3 spectra and to help provide information about the vibrational motions of the molecules examined. The 2-Cl-DPK radical was also observed in the TR3 spectra obtained in an IPA solvent. However, the yield of the 2-Cl-DPK radical and the hydrogen abstraction rate was observed to be significantly lower than that of the other ClBP examined here under the same experimental conditions. The results DFT calculations show that the 2-chloro substituent changes the geometry and the electron density of the molecular orbitals of the BP triplet so that the 2-chloro substituent reduces the hydrogen abstraction ability the triplet state, which is different the hypothesis put forward by some previous studies that an electron-withdrawing group should increase the photoreduction ability of BP derivatives. Norfloxacin (NF) and Enoxacin (EN) are representative derivatives of Fluoroquinolones (FQ). There are four forms of NF and EN and these different forms can coexist in aqueous solutions. The UV-vis absorption and resonance Raman (RR) spectra of NF and EN have been obtained in neat acetonitrile (MeCN), MeCN:HClO4-H2O/1:1 (pH?1), MeCN:H2O/1:1 (pH?7.5) and MeCN:NaOH-H2O/1:1 (pH?13) solutions. The species observed in the spectra are assigned by comparison of the experimental spectra to the DFT calculated spectra and the vibrational modes are also described from the results of the DFT calculations. The absorption spectra of NF and EN obtained in MeCN:H2O/1:1 solutions show that some other species coexist with the tautomeric forms in the neutral aqueous solution. The RR spectra of the tautomeric forms of NF and EN were obtained by subtraction of the RR spectra of the neutral and anionic forms from the RR spectra of NF and EN in neutral aqueous solutions. The results suggest that NF and EN exists in neutral, anionic and tautomeric forms in neutral aqueous solutions. The time dependant DFT calculation results suggest that the fluorine atom has little contribution to the lowest unoccupied molecular orbitals of the different forms of NF and EN. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Nanosecond time-resolved resonance Raman spectroscopy (ns-TR3), nanosecond transient absorption (ns-TA) and femtosecond transient absorption (fs-TA) were utilized to investigate the photochemistry of ketoprofen (KP), ketoprofen-purine dyads, fenofebric acid (FA) in different solutions. For KP, the rate constant and reaction mechanism of KP are strongly dependent on the concentration of water. In neat acetonitrile and acetonitrile-rich solutions (water:acetonitrile?1:1, v:v), KP exhibits mostly benzophenone-like photochemistry to give rise to triplet state which in turn transforms to ketyl radical intermediate by hydrogen abstraction reaction. However, in aqueous solutions with higher water ratios (water:acetonitrile?80%) or acidic solutions, fs-TA studies found that after the irradiation of KP the singlet state will transform into the triplet state with a high efficiency through an intersystem crossing and a triplet state mediated decarboxylation reaction of KP is confirmed in water-rich and acidic solutions as well as the triplet state KP- anion generating a KP carbanion through a decarboxylation reaction. Triplet state ketoprofen (3KP) is firstly observed by ns-TR3 experiments and then excited triplet state intramolecular proton transfer (ESIPT) induces 3KP to facilely undergo the decarboxylation reaction to generate a triplet protonated carbanion biradical (3BCH) species, this observation is also confirmed by the results from density functional theory (DFT) calculations. For solutions with higher water concentrations (such as between 50% and 90% water by volume), the hydrogen abstraction and decarboxylation processes are two competitive pathways with different rate constants. For KP-purine dyads, intramolecular hydrogen abstraction has been proposed to form ketyl-C1 biradical in acetonitrile solvent. Fs-TA study on KP-purine nucleoside dyads reveals that 3KP of cisoid dyads decays faster than 3KP of transoid dyads obtained in acetonitrile-water mixtures. Ns-TR3 experiments and DFT calculations suggest that ketyl-C1 biradical intermediate is generated with a higher efficiency for the 5-KP-dG dyad than for the 5-KP-dA and 5-KPGly-dA dyads. There is no ketyl-C1 biradical observed in ns-TR3 experiments for the 3-KP-dA dyad with transoid structure due to a steric effect. For FA, a solvent dependent photochemistry is observed. A typical nπ* triplet state FA (3FA) is evolved by a high efficient intersystem crossing in acetonitrile-rich solutions and subsequently 3FA promptly abstracts a hydrogen from water molecule to generate a ketyl radical intermediate. In contrast, an inversion of the hydrogen abstraction and decarboxylation reactions of nπ* 3FA is rationalized with the assistance of water molecules when going from acetonitrile-rich to water-rich mixtures. However, in 50% PBS solution, FA carbanion is observed from the picosecond to nanosecond times and the cleavage of FA carbanion gives rise to the enolate 3- anion at later nanosecond delay times. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy