The research work presented in this thesis is a consolidated report of experiments aimed at controlling the product selectivity in photochemical reactions. Water soluble hosts such as p-sulfonato calix[n]arenes (n= 6 or 8) and cyclodextrins have been used to solubilize organic molecules in water and to control the product selectivity. These host molecules control the product selectivity by their ability to encapsulate and interact with guest molecules. Furthermore, carrying out reactions in water as solvent is important from green chemistry point of view.

In this study, a synthetic, water soluble cavitand octa acid (OA) is used as medium for conducting photochemical reactions. The cavitand octa acid is soluble in water in slightly basic conditions. OA forms different types of complexes with variety of organic guest molecules. Remarkably, in presence of a hydrophobic guest, two of these OA molecules self assemble to form a capsular complex (guest@(OA)2). The confined inner phase of the cavitand can be utilized to control both photochemistry and photophysics of organic guest molecules. Stilbene derivatives undergo cis/trans (Z/E) photoisomerization in organic solvents. The results of our studies with stilbenes@(OA)2 suggest that the available free volume for encapsulated guest stilbenes could be manipulated by changing the number and position of the substituent methyl groups which has a significant influence on the photoisomerization process. Further, energy transfer from caged donor ((fluorenone)2@(OA)2) to caged acceptor ((stilbene)@(OA)2) was explored. It is also demonstrated that photoinduced electron transfer (PET) between acceptor (cationic) present outside the OA capsule to donor (a stilbene) present within the capsule is feasible and occurs at a higher than diffusion controlled rate. The PET in the above supramolecular system could be controlled by employing another cavitand, cucurbit[7]uril (CB7) to complex with cationic acceptor. Also, studies with carefully chosen guest molecules suggest that selective photocyclodimerization can be carried out within the inner phase of OA.

Thesis (Ph. D.) -- Virginia Commonwealth University, 2006. / Prepared for: Dept. of Chemistry. Bibliography: leaves 165-175. Also available online via the Internet.

Thesis (M.S.)--Oregon Graduate Center, 1976.

The syntheses and characterization of new dirhodium complexes based on the electron acceptor ligand dipyrido[3,2-a:2´,3´-c]phenazine (dppz) and its derivatives are reported. These complexes have been shown to photocleave pUC18 plasmid in vitro under irradiation with visible light which results in the nicked, circular form of DNA. Unlike typical DNA photocleavage agents, the new compounds are capable of photocleaving DNA in the absence of oxygen as well as in the presence of oxygen. The toxicity of the complexes which contain the electron acceptor dppz ligand toward human skin cells increases when the cell cultures are irradiated with visible light. In contrast, the photocytotoxicity of those complexes that do not contain the dppz do not differ from cytotoxicity in the dark. The chemistry of the newly synthesized dirhodium-dppz complexes with glutathione, which is considered to be an important molecule in the deactivation of metal-based drugs, has also been investigated. The results show that glutathione reversibly reduces [Rh2(µ-O2CCH3)2(dppz)2]2+ (6) and [Rh2(µ-O2CCH3)2(dppz)(bpy)]2+ (7), and that they are easily reoxidized to the original form in air. EPR measurements and DFT calculations indicate that the additional electron is delocalized in the ligand orbitals. The molecular characteristics that affect the in vitro activity of dirhodium complexes is discussed. The lability of the groups coordinated to the dirhodium complexes is a significant factor that influences the toxicity of the complexes. In addition, the presence of labile solvent molecules and monodentate acetate groups provide potential “open sites” accessible for nucleophilic substitution, as opposed to these sites being occupied by non-labile groups that reduce the reactivity of the complexes. Finally, the results also demonstrate that the carbonato-bridged complexes of the type [Rh2(µ-O2CO)2(diimine)2(H2O)2]2+ are useful precursors to access new dirhodium-diimine compounds that are not accessible from the acetate precursors. These compounds react with trifluoroacetamide, 2-pyrrolidinone, and trifluoroacetic acid to form products in which the carbonato ligands are substituted in favor of the new bridging group. This work provides a foundation for the preparation of new series of dirhodium complexes that contain the dppz ligand and bridging ligands other than acetate.

Several experiments were undertaken to investigate the mechanism of photodechlorination of pentachlorobenzene. The thermal methoxydechlorination reaction of pentachlorobenzene was studied. In DMSO at 50 °C sodium methoxide reacts smoothly with pentachlorobenzene to give three tetrachloroanisole isomers. A second-order kinetic plot for this reaction is linear to high precision, indicating that the reaction is second order overall. The rate of the reaction and the product regioisomer distribution are not affected by the presence of radical traps such as galvinoxyl, by reaction in the absence of oxygen or by benzyne intermediate traps such as 1,3-diphenylisobenzofuran. The rate of the reaction is reduced linearly as the starting mixture is diluted with methanol. These facts suggest that the reaction follows the classical S[subscript N]Ar mechanism. The proposed structure of the pentachlorobenzene radical anion formed by photolysis in the presence of triethylamine is analogous to the σ-complex intermediate in the S[subscript N]Ar reaction. The regiochemistry of these two types of dechlorination was compared and showed a fair correlation. The differences in regiochemistry were attributed to steric effects between the nucleophile and the aromatic ortho chlorine atoms in the S[subscript N]Ar reaction. Tetrachlorophenyl radicals were generated by thermal decomposition of 1 ,2,4,5-tetrachlorobenzeneazotriphenylmethane in the presence of CCl₄ and a hydrogen atom donor. The selectivies of chlorine versus hydrogen or deuterium atom abstraction were determined in several systems and applied to selectivity of atom abstraction observed in photochemical experiments. The results support the hypothesis that, in the photolysis of pentachlorobenzene in the presence of triethylamine, the intermediate tetrachlorophenyl radical exists as an unencumbered free radical rather than in a solvent caged pair with triethylamine. It was anticipated that the rate of photodechlorination would increase in micellar solutions if triethylamine was added. Experiments showed no such expected increase in rate, and showed regiochemistry similar to that of the same reaction in the absence of triethylamine. / Graduation date: 1992

No description available.

The syntheses and characterization of new dirhodium complexes based on the electron acceptor ligand dipyrido[3,2-a:2´,3´-c]phenazine (dppz) and its derivatives are reported. These complexes have been shown to photocleave pUC18 plasmid in vitro under irradiation with visible light which results in the nicked, circular form of DNA. Unlike typical DNA photocleavage agents, the new compounds are capable of photocleaving DNA in the absence of oxygen as well as in the presence of oxygen. The toxicity of the complexes which contain the electron acceptor dppz ligand toward human skin cells increases when the cell cultures are irradiated with visible light. In contrast, the photocytotoxicity of those complexes that do not contain the dppz do not differ from cytotoxicity in the dark. The chemistry of the newly synthesized dirhodium-dppz complexes with glutathione, which is considered to be an important molecule in the deactivation of metal-based drugs, has also been investigated. The results show that glutathione reversibly reduces [Rh2(µ-O2CCH3)2(dppz)2]2+ (6) and [Rh2(µ-O2CCH3)2(dppz)(bpy)]2+ (7), and that they are easily reoxidized to the original form in air. EPR measurements and DFT calculations indicate that the additional electron is delocalized in the ligand orbitals. The molecular characteristics that affect the in vitro activity of dirhodium complexes is discussed. The lability of the groups coordinated to the dirhodium complexes is a significant factor that influences the toxicity of the complexes. In addition, the presence of labile solvent molecules and monodentate acetate groups provide potential “open sites” accessible for nucleophilic substitution, as opposed to these sites being occupied by non-labile groups that reduce the reactivity of the complexes. Finally, the results also demonstrate that the carbonato-bridged complexes of the type [Rh2(µ-O2CO)2(diimine)2(H2O)2]2+ are useful precursors to access new dirhodium-diimine compounds that are not accessible from the acetate precursors. These compounds react with trifluoroacetamide, 2-pyrrolidinone, and trifluoroacetic acid to form products in which the carbonato ligands are substituted in favor of the new bridging group. This work provides a foundation for the preparation of new series of dirhodium complexes that contain the dppz ligand and bridging ligands other than acetate.

Thesis (Ph. D.)--Ohio State University, 2008.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 155-163).