Stark and Zeeman effects in the lowest excited states of [Zn(bpy) 3](ClO 4) 2:Ru(II). Localized triplet metal-to-ligand charge transfer transitions

Abstract

Polarized absorption spectra of the metal-to-ligand charge transfer (MLCT) transitions in the title system are reported. Strong linear dichroisms are observed in accord with the crystal structure which shows that only two of the bpy ligands are crystallographically equivalent. The MLCT transitions to the third ligand are found to lie several hundred wavenumbers higher in energy. A strong angular dependence of the Zeeman effect in luminescence is observed when varying the direction of the magnetic field in the metal-ligand plane. These patterns are quantitatively analyzed in terms of localized transitions. The three lowest-excited electronic states are well described as the components of an orbitally non-degenerate spin triplet state with a very large zero field splitting. All three lowest-energy origins show the same large splitting in an applied electric field, confirming their charge-transfer nature. Luminescence and excitation line narrowing experiments establish that the splitting is a pseudo-Stark effect. Stark-swept transient hole-burning experiments provide a homogeneous line width of ≈ 15 MHz for the origin II in [Zn(bpy) 3](CIO 4) 2:Ru(II) at 1.8 K.