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 (Δ λ max = 195 nm) for 1 (PF 6 ) 2 , 465 and 627 nm (Δ λ max = 162 nm) for 2 (PF 6 ) 2 , and 455 and 608 nm (Δ λ 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.