Content area
Abstract
Solvatochromism is the dependence of a solute's electronic transition energy on the solvent environment. (Ru(NH$\sb3)\sb4$bipyridine) $\sp{2+}$ has three solvatochromic metal-to-ligand charge transfer bands, one in the near-UV and two that are almost completely overlapped in the visible. Previous researchers concluded that the solvatochromicity was due to the hydrogen bonding of the solvent with the ammine ligands, which resulted in an increased stability of Ru$\sp{3+}$ relative to Ru$\sp{2+}$ as the electron donating ability of the solvant is increased. The solvatochromic shift of the solute's transition energy depends on the differential solvation of the solute's ground and excited states and on each state's electronic and nuclear characteristics. This is reflected in the peak energy of an electronic transition, which is the sum of the solvent reorganization energy and the 0-0 and internal reorganization energies of the solute. In this work, the 0-0, internal, and solvent reorganization energies were experimentally determined for (Ru(NH$\sb3)\sb4$bipyridine) $\sp{2+}$ in methanol and dimethylsulfoxide by modeling the absorption and Raman excitation profiles with time-dependent spectroscopy theory. The Raman spectra were excited at frequencies resonant with both visible bands and below resonance with the near-UV band. Consequently, the polarizability tensor components that were due to the visible bands were simulated with time-dependent expressions and the component due to the near-UV band was incorporated with a phenomenological function. The results of this work are presented in the context that (Ru(NH$\sb3)\sb4$bipyridine) $\sp{2+}$ adopts $C\sb{s}$ symmetry, which is in qualitative agreement with our spectroscopic observations and the electro-optical absorption data of Hug and Boxer. The results of the modeling indicate that the solvatochromic shift of approximately 900 cm$\sp{-1}$ of both transitions is due almost entirely to changes in the 0-0 energy; also, they suggest that the visible transitions are nearly degenerate and share similar electronic and nuclear characteristics.
