Date of Award
Summer 1992
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Kincaid, James R.
Second Advisor
Nakamoto, Kazuo
Third Advisor
Steinmetz, Mark G.
Abstract
Ru(II) polypyridine complexes have attracted wide interest in view of their potential utility in solar energy conversion devices. The experimental efforts have been directed towards understanding the basic physicochemical properties of these complexes and improvement of their performance as photosensitizers. In the latter case the major goals are: increasing the lifetime of the excited electronic states, eliminating photodegradation and preventing rapid back-electron-transfer processes. In order to achieve these goals two routes can be followed. One involves modification of coordinated ligands while in the other investigated molecules are incorporated into organized media. Y-zeolites are particularly attractive because their large supercages can accommodate ruthenium tris-polypyridine complexes.
Several zeolite-Y-entrapped homo and heteroleptic tris polypyridine complexes of Ru(II) have been synthesized. Several synthetic aspects, peculiar to the intra-zeolite chemistry, have been observed. These include ligand exchange and formation of the zeolite-bound ruthenium species. The electronic absorption and emission spectra of the free and zeolite-entrapped complexes have been obtained. In order to investigate possible structural alterations in both ground and excited electronic states of the entrapped compounds, resonance Raman and time-resolved resonance Raman spectra have been acquired. Excited electronic state lifetimes have been measured and compared with the results for aqueous solutions. While relatively small electronic and structural perturbations are induced by zeolite supercages, substantial modifications of the excited state lifetimes in zeolite matrices have been observed. These effects are attributed to the zeolite-induced modifications of the excited state decay occurring via thermally populated $\sp3$dd metal-localized states.
In order to investigate mechanisms of the excited state energy dissipation in the Ru(bpy)$\sb3\sp{2+}$ system the excited state lifetimes of several selectively deuteriated bipyridine analogues were obtained. These results indicate position-dependence of deuteration on the observed lifetimes. The changes in the excited state lifetimes observed upon deuteration of bpy in Ru(bpy)$\sb3\sp{2+}$ were explained in terms of shifts of vibrational frequencies of the critical acceptor mode.