Dual-Emissive Monoruthenium Complexes of N(CH(3))-Bridged Ligand: Synthesis, Characterization, and Substituent Effect

Three monoruthenium complexes 1(PF(6))(2)–3(PF(6))(2) bearing an N(CH(3))-bridged ligand have been synthesized and characterized. These complexes have a general formula of [Ru(bpy)(2)(L)](PF(6))(2), where L is a 2,5-di(N-methyl-N’-(pyrid-2-yl)amino)pyrazine (dapz) derivative with various substituents, and bpy is 2,2′-bipyridine. The photophysical and electrochemical properties of these compounds have been examined. The solid-state structure of complex 3(PF(6))(2) is studied by single-crystal X-ray analysis. These complexes show two well-separated emission bands centered at 451 and 646 nm (Δλ(max) = 195 nm) for 1(PF(6))(2), 465 and 627 nm (Δλ(max) = 162 nm) for 2(PF(6))(2), and 455 and 608 nm (Δλ(max) = 153 nm) for 3(PF(6))(2) in dilute acetonitrile solution, respectively. The emission maxima of the higher-energy emission bands of these complexes are similar, while the lower-energy emission bands are dependent on the electronic nature of substituents. These complexes display two consecutive redox couples owing to the stepwise oxidation of the N(CH(3))-bridged ligand and ruthenium component. Moreover, these experimental observations are analyzed by computational investigation.