Synthesis, characterization, electrochemistry,a nd photophysicso fh omo-a nd heteroleptic ruthenium(II) complexes [Ru(cpmp) 2 ] 2 + (2 2 + + )a nd [Ru(cpmp)(ddpd)] 2 + (3 2 + + ) bearing the tridentate ligands 6,2''-carboxypyridyl-2,2'-methylamine-pyridyl-pyridine( cpmp)a nd N,N'-dimethyl-N,N'-dipyridin-2-ylpyridine-2,6-diamine (ddpd) are reported. The complexes possess one (3 2 + + )o rt wo (2 2 + + )e lectron-deficient dipyridyl ketone fragments as electron-accepting sites enabling intraligand charget ransfer (ILCT), ligand-to-ligand charge transfer (LL'CT) and low-energy metal-to-ligand charge transfer (MLCT) absorptions. The latter peak around 544 nm (green light). Complex 2 2 + + shows 3 MLCT phosphor-escencei nthe red to near-infrared spectral region at room temperature in deaerated acetonitrile solution with an emission quantum yield of 1.3 %a nd a 3 MLCT lifetimeo f4 77 ns, whereas 3 2 + + is much less luminescent. This different behavior is ascribed to the energy gap law and the shape of the parasitic excited 3 MC state potential energy surface. This study highlights the importance of the excited-state energies and geometries for the actual excited-state dynamics. Aromatic and aliphatic amines reductively quench the excited state of 2 2 + + paving the way to photocatalytic applications using low-energyg reen light as exemplified with the green-light-sensitized thiol-ene click reaction.Scheme1.Benchmarkruthenium(II) complexesa nd their absorption/ emission band maxima.[a] J.Scheme3.Photocatalytic radical thiol-eneclick reaction utilizing the (green) light-induced reductive quenching pathway of [RuLL] 2 + = 2 2 + + , 3 2 + + and [Ru(bpy) 3 ] 2 + mediated by p-toluidine (Ar = p-C 6 H 4 -CH 3 )a ccordingt oref.[71] (R = CH 2 -CHNHBoc-COOCH 3 ).
Push‐pull substituted ruthenium(II) complexes strongly absorb green light and emit in the red to near‐infrared spectral region with a quantum yield of 1.3 % and a lifetime of the emissive triplet MLCT state of 477 ns. Amines reductively quench the long‐lived excited state enabling photoredox chemistry (light‐sensitized thiol‐ene click reaction) with green light. More information can be found in the Full Paper by K. Heinze et al. on page 6820.
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