Excited-state absorption and circular dichroism of ruthenium(II) tris(phenanthroline) in the ultraviolet region.

Excitation of ruthenium(II) tris(phenanthroline) in the visible region results in the tranfer of an electron from the central atom toward one of the ligands. To probe this excited state, we have performed pump-induced absorption and circular dichroism in the ultraviolet wavelengths, in the intraligand pi-pi* transition region. On top of the bleaching of the ground state transitions, new structures appear in the absorption and CD spectra. Thanks to a classical calculation based on the polarizability theory, we can interpret these features as the result of a strong reduction of the excitonic coupling due to a blue shift of the pi-pi* transition in the reduced ligand accompanied by the onset of new excited-state transitions.