Investigation of transition metal complexes with potential photochemical applications

One of the advantages of using light as a reactant in a chemical reaction is the generation of an excited state that is able to overcome high activation barriers that are not accessible by heating. In addition, the light can be spatially controlled, by focusing the photons onto a given area; such control is not possible in conventional thermal reactions. The spatial control of light has been shown to be advantageous in a number of applications including cancer therapy, signaling, and data storage. The photophysical properties and photochemistry of various complexes that may be potentially useful in these three applications will be discussed in this dissertation.;The complex cis-[Rh2(mu-O2CCH 3)2(CH3CN)6]2+ exchanges the two axial CH3CN ligands for solvent molecules in water to yield cis-[Rh2(mu-O2CCH3) 2(CH3CN)4(H2O)2] 2+. Photolysis of cis-[Rh2(mu-O 2CCH3)2(CH3CN)4(H2 O)2]2+ in H2O results in the photoaquation of two equatorial CH3CN ligands to yield cis-[Rh 2(mu-O2CCH3)2(CH3CN) 2(H2O)4]2+, a complex that is able to covalently bind to free 2,2'-bipyridine (bpy) and 9-ethylguanine in solution, as well as double-stranded DNA (lambdairr ≥ 455 nm). cis-[Rh2(mu-O2CCH3)2(CH 3CN)4(H2O)2]2+ exhibits 20-fold lower cytotoxicity towards human skin cells than of hematoporphyrin in the dark, and its toxicity increases by a factor of 34 when irradiated with visible light (400--700 nm, 30 min). This increase in cytotoxicity by cis-[Rh2(mu-O2CCH3) 2(CH3CN)4(H2O)2] 2+ upon irradiation is ∼7 times greater than that measured for hematoporphyrin. These properties make cis-[Rh2(mu-O 2CCH3)2(CH3CN)4(H2 O)2]2+ a promising photo-cisplatin analog and a potential agent for photodynamic therapy. To our knowledge, cis-[Rh2(mu-O2CCH3)2(CH 3CN)4(H2O)2]2+ is the first metal-metal bonded complex to bind to DNA upon irradiation with visible light. Various substituted dirhodium tetraformamidinate complexes, Rh 2(R-form)4 (R = p-CF3, p-Cl, p-OCH3, m-OCH 3; form = N,N'-diphenylformamidinate), and the new complex Rh2(tpgu)4 (tpgu = 1,2,3-triphenylguanidinate) were investigated as potential agents for the photoremediation of saturated halogenated aliphatic compounds, RX (R = alkyl group). The synthesis and characterization of the complexes is reported, and the crystal structure of Rh2(tpgu)4 is presented. The lowest energy transition of the complexes is observed at ∼870 nm and the dirhodium systems react with alkyl chlorides and alkyl bromides under low energy irradiation (lambdairr > 795 nm), but not when kept in the dark. The metal-containing product of the photochemical reaction with RX (X = Cl, Br) is the corresponding mixed-valent Rh2(II,III)X (X = Cl, Br) complex, and the crystal structure of Rh2( p-OCH3-form)4Cl generated photochemically from the reaction of the corresponding Rh2(II,II) complex in CHCl 3 is presented. In addition, the product resulting from the dimerization of the alkyl fragment, R2, is also formed during the reaction of each dirhodium complex with RX. A comparison of the dependence of the relative reaction rates on the reduction potentials of the alkyl halides and their C-X bond dissociation energies are consistent with an outer-sphere mechanism. In addition, the relative reaction rates of the metal complexes with CCl 4 decrease with the oxidation potential of the dirhodium compounds. The mechanism of the observed reactivity is discussed and compared to related systems.;The DNA light-switch complex [Ru(bpy)2(tpphz)]2+ (tpphz = tetrapyrido[3,2-a:2',3'-c:2',2'- h:2',3'-j]phenazine) is luminescent when bound to DNA and in organic solvents and weakly emissive in water. To date, light-switch behavior by transition metal complexes has generally been regarded as confirmation of DNA intercalation. In contrast, the present work demonstrates that the non-intercalating bimetallic complex [(bpy)2Ru(tpphz)Ru(bpy) 2]4+ behaves as a DNA light-switch. Weak emission from the 3MLCT excited state of [(bpy)2Ru(tpphz)Ru(bpy) 2]4+ is observed in water with lambdaem = 623 nm (phiem = 1.4 x10--4), and a red-shift (lambdaem = 702 nm) and 40-fold increase in intensity is observed upon addition of 100 muM ct-DNA. Addition of increasing concentrations of [(bpy)2Ru(tpphz)Ru(bpy)2]4+ to 1 mM herring sperm DNA does not result in an increase in the viscosity of the solution, indicating that the complex is not an intercalator. (Abstract shortened by UMI.)...