High-valent transition metal-oxo intermediates are of fundamental importance because of their central role as active oxidizing species in enzymatic and synthetic catalytic oxidations. Many transition metal catalysts have been extensively studied as models of the ubiquitous cytochrome P450 enzymes to probe the sophisticated oxygen atom transfer mechanism as well as to invent enzyme-like oxidation catalysts. In this work, photolysis of highly photo-labile corrole-manganese(IV) bromates or nitrites by visible light was studied in two corrole systems with different electronic environments. The corrole systems under studied include 5,10,15- tris(pentafluorophenyl)corrole (TPFC) and 5,10,15-triphenylcorrole (TPC). As observed in both systems, homolytic cleavage of O-Br or O-N bonds in the ligands resulted in one-electron photo-oxidation to generate corrrole-manganese(V)-oxo species, as determined by their distinct UV-vis spectra and kinetic behaviors. The kinetic of oxygen atom transfer (OAT) reactions with various substrates by these photogenerated [MnV(Cor)(O)] were studied in CH3CN and CH2Cl2 solutions. [MnV(Cor)(O)] exhibits remarkable solvent and ligand effects on its reactivity and spectral behaviors. In the more electron-deficient TPFC system and in the polar solvent CH3CN, MnV-oxo corrole returned MnIII corrole in the end of oxidation reaction. However, in the less polar solvent CH2Cl2 or in the less electron-deficient TPC systems, MnIV product was formed instead of MnIII. With the same substrates and in the same solvent, the order of reactivity of MnV-oxo corrole was inverted as TPC > TPFC. The spectra and kinetic results are rationalized by a multiple oxidation model, where the electron-demand MnVoxo species may serve as direct two-electron oxidation for oxygen atom transfer reactions; and less electron-demand systems undergo a disproportionation reaction to form a putative manganese(VI)-oxo corrole as the true oxidant. The choice of pathways is strongly dependent on the nature of the solvent and corrole ligand. Furthermore, porphyrin-manganese(V)-oxo were produced in organic solvents by visible light irradiation of the corresponding porphyrin-manganese(III) nitrite complexes. The porphyrin systems studied were 5,10,15,20-tetrakispentafluoro phenylporphyrin (TPFPP), 5,10,15,20-tetrakis(2,6-difluorophenyl)porphyrin (TDFPP) and 5,10,15,20-tetrakis(2,6-dichlorophenyl)-porphyrin (TDCPP). Heterolytic cleavage of O-N bond of nitrite ligand results in two-electrons photo-oxidation. Under visible light irradiation, MnV-oxo porphyrins quickly returned to MnIII product. However, in absence of light, MnIV-oxo species were formed, as determined by their distinct UV-vis spectra, which permitted direct kinetic studies. The apparent rate constants for reaction of [MnIV(Por)(O)] species show inverted reactivity order with (TPFPP) < (TDFPP) < (TDCPP) in reactions with ethylbenzene. A model for oxidation under catalytic condition was presented.

No description available.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on June 28, 2009). Includes bibliographical references (p. 189-202).

No description available.

Thesis (Ph.D.)--York University, 2005. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 199-210). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNR11608

Chlorotoluron photochemical degradation in homogeneous phase (aqueous solutions) was studied. Photolysis by UV radiation, influence of metal (ferric, ferrous) ions, pH, and solvent composition on the reaction rate was investigated. Photosensitizing effect of humic samples was tested. Kinetic characteristics (rate constants, overall quantum yield), products of reactions and extent of mineralization was evaluated.

The nature and scope of this problem is to determine from the irradiation of isopropyl alcohol with 2537 A, the behavior and mechanism of the reaction, since it is known that a reaction does occur.

The photochemical reactions occurring in aqueous solutions of octacyanomolybdate(V) ion, Mo(CN)_8^3-, during irradiation with light of 365 and 436 nm wavelengths were studied. The quantum yields and reaction products were determined for neutral, unbuffered solutions as well as solutions buffered at pH 4.0, 7.0, and 9.0. The results of these studies showed that the Mo(CN)_8^3- ion is rapidly reduced by light to a Mo(IV) complex. In neutral or acidic media, the initial photoreduction product was found to be the red heptacyanoaquomolybdate(IV) ion, Mo(CN)_7(H_2O)^3-. Photolysis in basic solution gave the yellow heptacyanohydroxomolybdate(IV) ion, Mo(CN)_7(OH)^4-, as an unstable intermediate. Hydrolysis of this complex to the blue tetracyanohydroxooxomolybdate(IV) ion, Mo0(OH)(CN)_4^3-, occurred rapidly in base. In each case, cyanogen, (CN)_2, and cyanate ion, OCN^-, were formed. Additionally, in neutral solutions, the formation of hydrogen ion during the irradiation of the sample gave a rapid drop in the pH of the solution. Measurements of the product quantum yields for Mo(IV) complexes, *_Mo(IV), gave values that were always greater than one and which increased rapidly with increasing pH of the irradiated solutions, The values were the same for both irradiating wavelengths, showing no wavelength effect for the reaction, The quantum yields determined for *_Mo(IV) were 1.51, 1.59, 3.10, and 4.29 for pH 4 , neutral pH, pH 7, and pH 9 solutions respectively. From the experimental results, a reaction mechanism is suggested for each of the aqueous media used, The initial photolytic reactions are the same in all solutions with subsequent thermal reactions being responsible for the variation of *_Mo(IV) with the pH of the solution.

This research has focused on the sensitized photoisomerization step of a solar energy storage system based on the interconversion of norbornadiene (NBD) and quadricyclane (Q). Sensitizers studied in the photoisomerization were arylphosphine complexes of copper(I) halides [(Ph_3P)_3CuX, (MePh_ 2P)_3CuX, (DIPHOS)CuCl; X = Cl, Br, I and DIPHOS = Ph_ 2P(CH_2)_2PPh_2]. The lowest electronic excited state of the complexes can be an effective triplet energy sensitizer as evidenced by a maximum quantum yield of 1.0 with (HePh_2P)_3CuX. The sensitization mechanism of the L_3CuX complexes is proposed as a bimolecular energy transfer process in which energy transfer takes place through the metal centered orbitals. The efficiency of the (MePh_ 2P)_3CuX sensitizers is unprecedented by other reported inorganic or organic sensitizers; however, ligand dissociation of the complexes in dilute solutions detracts from their otherwise attractive features. The free ligands undergo rapid photodecomposition and are extremely poor sensitizers of the NBD/Q system. The ligand dissociation of the L_mCu_nCl_n (L = Ph_3P, MePh_2P; m:n = 3:1, 2:1, 4:2, 3:2, 2:2) complexes was modeled by use of vapor pressure osmometry and UV absorption. The equilibria and equilibrium constants of dissociation were determined for benzene solutions at 37 °c. The stability of the L_mCu_nCl_n complexes (Ph_3P<< MePh_2P) toward ligand dissociation is attributed to the larger steric requirements of Ph_3P in comparison to MePh_2P. Evidence for ground state complexation of NBD and the L_mCu_nCl_n compounds (m:n < 3:1) is shown. Photoexcitation of the (NBD) L_mCu_nCl_n (m:n < 3:1) complexes can produce Q but with quantum efficiencies < 1.0. Photophysical properties of the arylphosphines and their copper(I) halide complexes are reported. The lowest electronic transition of the phosphines associated with an obscured absorption band at ~300nm is classified as an l -> a_pi transition. Coordination to copper() halides brings about an enhancement of the l -> a_pi transition of the ligand. The term o,d ->a_pi is used to describe the lowest electronic transition of the complexes indicating that both the o bond of the phosphorus lone electron pair to the metal and the d-d orbital bonding of the metal to the phosphorus are involved in an electron excitation from the phosphorus to an antibonding phenyl-pi-system (a_pi ). The photophysical properties of Zn(II), Cu(I), and Ni(O) complexes of MePh_2P are shown to follow the concept of a o,d -> a_pi electronic transition.

Approved for public release; distribution is unlimited / The production of nitric oxide by soft solar X-rays in the E-region of the ionosphere is investigated. An empirical expression for the variation in X-ray flux as a function of F10.7 is determined. This expression is incorporated into a one-dimensional diffusive photochemical model to compute nitric oxide densities. No results of these calculation are compared with NO observation from the Solar Mesosphere Explorer satellite. Variations of X-ray flux by a factor of 30 over the solar cycle can explain the observed variation in nitric oxide densities. / http://archive.org/details/investigationofp00duma / Lieutenant, United States Navy