Triazole‐Bridged Dinuclear Ru(II) and Ir(III) Complexes: Photophysics, Electrochemistry, and DFT/TD‐DFT Analysis

The heteroditopic 1,2,3-triazole ligand 4-[4-(pyridin-2-yl)-1,2,3-triazol-1-yl]-2,2′-bipyridine (L3), prepared here following a reported CuAAC procedure, was employed as a bridging scaffold for the synthesis and study of dinuclear Ru(II) and Ir(III) complexes. The bis-ruthenium [{Ru(bpy)2}2(L3)](PF6)4 (Ru3) and bis-iridium [{Ir(ppy)2}2(L3)](PF6)2 (Ir3) species were prepared and fully characterized, and their electrochemical and photophysical properties were compared with those of mononuclear model complexes of the bipyridyl (L1) and pyridyl–triazole (L2) domains (Ru1–2 and Ir1–2). Cyclic voltammetry shows quasi-reversible Ru(II)/Ru(III) and Ir(III)/Ir(IV) couples in the range 0.89–1.00 V versus Fc+/Fc, with Ru3 and Ir3 displaying single, slightly broadened oxidation waves consistent with two closely spaced one-electron processes at electronically decoupled metal centers. In deaerated acetonitrile, Ru1 and Ir1 exhibit redshifted 3MLCT/3LLCT emission compared to [Ru(bpy)3]2+ and [Ir(ppy)2(bpy)]+, respectively, while Ru2 is weakly emissive and Ir2 displays structured 3LC emission with high quantum yield. The dinuclear complexes Ru3 and Ir3 show further redshifted emission (λmax = 664 and 666 nm, respectively) and modified lifetimes relative to the mononuclear analogues. DFT/TD-DFT calculations indicate a triazole/bipyridyl-centered acceptor (LUMO) and near-isoenergetic, metal-centered HOMO/HOMO–1 levels localiZed on different termini in the dinuclear species, rationalising the weak intermetallic coupling and spectral tuning enabled by L3.