Resonance Raman and time-resolved resonance Raman investigations of tris(bipyridine)ruthenium(II) and related complexes

Gerald David Danzer, Marquette University

Abstract

The metal-to-ligand charge transfer (MLCT) excited states of tris(2,2$\sp\prime$-bipyridine)ruthenium(II) and related complexes have been the subject of intense interest. Resonance Raman (RR) spectroscopy is an ideally suited probe for both ground and excited states. In this research, RR spectroscopy is utilized to facilitate the understanding of the structural and electronic factors which influence the excited state dynamics of these complexes. The RR and time-resolved resonance Raman (TR$\sp3$) spectra of twelve isotopomers of Ru(bpy)$\sb3\sp{2+}$ are reported. These data are used to derive a ground state force field and the corresponding force field for the anion-radical fragment of the $\sp3$MLCT excited state. The normal mode formulations for the ground and $\sp3$MLCT excited state are compared and the structural implications for the $\sp3$MLCT state are discussed. Finally, the potential utility of these normal mode formulations in elucidating the nonradiative decay of the $\sp3$MLCT excited state is discussed. Inasmuch as the $\sp3$MLCT excited state of Ru(bpy)$\sb3\sp{2+}$ is ligand localized, the anion radicals of 2,2$\sp\prime$-bipyridine were independently investigated. The RR spectra of the lithium complexes of the 2,2$\sp\prime$-bipyridine anion radical and five isotopically labeled analogues are reported. The fundamental modes of vibration, excluding the C-H stretching and several low-frequency modes, are identified. The assignment of the vibrational frequencies to the fundamental modes of Libpy are supported by a normal coordinate calculation and the structural implications of the vibrational frequency shifts, relative to the neutral parent, are discussed. RR and TR$\sp3$ methods were also employed to investigate the electronic structures of the ground and lowest excited states of heteroleptic complexes of ruthenium(II) with bipyridine and bipyrazine. The RR spectra permit assignment of the electronic absorption bands to specific MLCT transitions. The TR$\sp3$ results document specific population of bipyrazine-localized excited states in the heteroleptic complexes. In addition, the present studies provide support for the enhancement of "neutral ligand" modes in the TR$\sp3$ spectrum. The effect of protonation of the peripheral nitrogen atoms in Ru(bpz)$\sb3\sp{2+}$ were also investigated by RR and TR$\sp3$ spectroscopy.

Recommended Citation

Gerald David Danzer, "Resonance Raman and time-resolved resonance Raman investigations of tris(bipyridine)ruthenium(II) and related complexes" (January 1, 1990). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. Paper AAI9101413.
http://epublications.marquette.edu/dissertations/AAI9101413

Share

COinS