## LSU Historical Dissertations and Theses

1990

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

John B. Hopkins

#### Abstract

Solvent effects in D$\sb3$ symmetric ruthenium-polypyridine complexes were studied by using excited state resonance Raman technique. Picosecond laser techniques were used to determine if electron transfer between ligands could be observed in an effort to learn about electron localization in ruthenium-polypyridine complexes. Ru(bpy)$\sb3\sp{2+}$ (bpy is 2,2$\sp\prime$-bipyridine), Ru(bpym)$\sb3\sp{2+}$ (bpym is 2,2$\sp\prime$-bipyrimidine), and Ru(Me$\sb2$-bpy)$\sb3\sp{2+}$ (Me$\sb2$-bpy is 4,4$\sp\prime$-dimethyl-2,2$\sp\prime$-bipyridine) were investigated in viscous glycerol solution at room temperature and -15$x$C. The viscosities of glycerol at these temperatures are 1487cP and 66500cP, respectively. It was found that in all three metal complexes investigated metal-to-ligand-charge-transfer state is already localized on the time scale of less than 30ps in spite of these high viscosity. In addition, it was found that the interligand electron coupling was not strong enough to overcome the vibrational reorganization energy. As a result, delocalization of electron density over all three ligands cannot occur and the solvents do not play a major role in the MLCT state of those metal complexes. The interpretation of the mechanism responsible for producing this result is presented based on quantum mechanical electron transfer theory. In these metal complexes, it is also known that interligand electron transfer takes place in heteroligand substituted complexes. In order to investigate this kind of interligand electron transfer, Ru(bpym)$\sb2$(bpy)$\sp{2+}$ and Ru(Me$\sb2$-bpy)$\sb2$(bpy)$\sp{2+}$ were studied in glycerol and in water at room temperature. It was determined that the former complex has fast interligand electron transfer rate (k$\sb{\rm ILET}$ $\geq$ 2 $\times$ 10$\sp{11}$) and the latter complex has slow interligand electron transfer rate (k$\sb{\rm ILET}$ $\geq$ 2 $\times$ 10$\sp6$) in water. By changing the viscosity from 1cP (water at room temperature) to 1487cP (glycerol at room temperature), a solvent dependence of interligand electron transfer was investigated. The result is that in spite of the dramatic change of the viscosity there are no dynamics observed in these metal complexes. These results were interpreted to indicate that interligand electron transfer occurs in the upper electronic states, or singlet metal to ligand charge transfer state.

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