Abstract
Abstract Phosphorescence energy transfer within ligand bridged diruthenium(II) compounds of the form [(bpy)2Ru(II)(B)Ru(II)(becbpy)2]4+, where bpy, becbpy, and B are 2,2′-bipyridine, 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine, and a bridging ligand, respectively, was investigated in butyronitrile solution in the temperature range 77—330 K. Excitation energy transfer occurs from the Ru(bpy)22+ moiety to the Ru(becbpy)22+ moiety. The energy transfer rate (kEN = (0.4—7.4) × 106 s−1) at 77 K is weakly dependent on the Ru2+–Ru2+ distance (r), which is estimated for the extended conformer of the bridging ligand. A linear plot of log kEN vs. log (1/r6) shows that energy transfer occurs via the dipole–dipole interaction. The weak temperature-dependence of the energy transfer rate in the temperature range 77—110 K is explained in terms of the absorption-emission coupling integral. The fast energy transfer (55 × 106 s−1) within [(bpy)2Ru(bpbimH2)Ru(becbpy)2]4+ (bpbimH2 = 2,2′-di-(2-pyridyl)-6,6′-bibenzimidazole) at 77 K is ascribed to the substantial exchange interaction between the Ru(bpy)2(bpbimH2)2+ moiety in the excited state and the Ru(becbpy)22+ moiety in the ground state.
Published Version
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