Monosubstitution of 1H-Imidazo[4,5-f][1,10]phenanthroline Ligands Yields Maximum Luminescence Quantum Yield in Ruthenium Polypyridyl Complexes

Six different monoarylated N-aryl-1H-imidazo[4,5-f][1,10]phenanthroline (Rip) ligands and their corresponding ruthenium complexes [(tbbpy)(2)Ru(Rip)](2+) Ru(Rip) have been synthesized bearing different aryl substituents on the imidazole unit including electron donating and accepting groups. N,N'-disubstitution on the imidazole unit yielded five new 1-aryl-3benzyl-1H-imidazo[4,5-f][1,10]phenanthrolinium bromide (RR'ip)(+) ligands and the corresponding ruthenium complexes [(tbbpy)(2)Ru(RR'ip)](3+) Ru(RR'ip). All complexes were characterized in terms of their structural, photophysical, photochemical and electrochemical properties. The photophysical data revealed a high luminescence quantum yield (21.6-22.8%) for monoarylated Ru(Rip) complexes compared to [Ru(bpy)(3)](2+) (9.5%) under inert conditions. Generating the imidazolium unit, yielding Ru(RR'ip)-complexes lead to notable loss of quantum yields. Furthermore, we observed an enhanced photostability of Ru(RR'ip) complexes in the case of ortho substituted aryl groups.