Isotope-induced shifts of electronic transitions: application to [Ru(bpy- h8) 3] 2+ and [Ru(bpy- d8) 3] 2+ in [Zn(bpy- h8) 3](ClO 4) 2

Abstract

The emission spectra resulting from the lowest excited states of the title compounds exhibit well-resolvable sturctures. A large number of vibronic satellites is identified and assigned. No dominant vibrational progression occurs. It is found that the electronic origins of the three lowest excited states are blue-shifted through deuteration by ≈ 1.7 cm −1/proton. This value is compared to shifts found for other compounds. It is shown that the amount of deuteration-induced shift has important and general implications with regard to differences of potential hypersurfaces between electronic ground and excited states of molecules. Thus, the blue-shift per proton observed for the title compounds is only twice as large as that for Cr(III) hexamine (for the 4A 2g(t 3 2g) ↔ 2E g(t 3 2g) transition known to exhibit very similar ground- and excited-state properties), while it is smaller by a factor of twenty than that for benzene (for the π-—π* bonding-antibonding transition). These considerations and the analysis of the vibronic spectra allow one to conclude that there are very similar potential hypersurfaces for the ground and the three lowest excited states of the title compounds. An electron localization on one bpy-ligand can be excluded for these excited states during the total time of electronic excitation.