Synthesis, characterization and photophysics of alkyne bridged bimetallic rhenium(I) and ruthenium(II) complexes

Six new homobimetallic and heterobimetallic complexes of rhenium(I) and ruthenium(II) bridged by ethynylene spacer [(CO)3(bpy)Re(BL)Re(bpy)(CO)3]2+ [Cl(bpy)2Ru(BL)Ru(bpy)2Cl]2+ and [(CO)3(bpy)Re(BL)Ru(bpy)2Cl]2+ (bpy = 2,2′-bipyridine, BL = 1,2-bis(4-pyridyl)acetylene (bpa) and 1,4-bis(4-pyridyl)butadiyne (bpb) are synthesized and characterized. The electrochemical and photophysical properties of all the complexes show a weak interaction between two metal centers in heterobimetallic complexes. The excited state lifetime of the complexes is increased upon introduction of ethynylene spacer and the transient spectra show that this is due to delocalization of electron in the bridging ligand. Also, intramolecular energy transfer from ∗Re(I) to Ru(II) in Re–Ru heterobimetallic complexes occurs with a rate constant 4 × 107 s−1.