Photocatalytic Hydrogen Evolution Driven by a Heteroleptic Ruthenium(II) Bis(terpyridine) Complex

Since the initial report by Lehn et al. in 1979, ruthenium tris(bipyridine) ([Ru(bpy)(3)](2+)) and its numerous derivatives were applied as photosensitizers (PSs) in a large panel of photocatalytic conditions while the bis(terpyridine) analogues were disregarded because of their low quantum yields and short excited-state lifetimes. In this study, we prepared a new terpyridine ligand, 4'-(4-bromophenyl)-4,4 ''':4,4 ''''-dipyridinyl- 2,2':6',2 ''-terpyridine (Bipytpy) and used it to prepare the heteroleptic complex [Ru(Tolyltpy)(Bipytpy)](PF6)(2) (1; Tolyltpy = 4'-tolyl-2,2':6',2'-terpyridine). Complex 1 exhibits enhanced photophysical properties with a higher quantum yield (7.4 x 10(-4)) and a longer excited-state lifetime (3.8 ns) Directional electron transfer using compared to those of [Ru(Tolyltpy)(2)](PF6)(2) (3 x 10(-5) and 0.74 ns, respectively). a heteroleptic Ru bis-terpyridine complex These enhanced photophysical characteristics and the potential for PS-catalyst interaction through the peripheral pyridines led us to apply the complex for visible-light-driven hydrogen evolution. The photocatalytic system based on 1 as the PS, triethanolamine as a sacrificial donor, and cobaloxime as a catalyst exhibits sustained activity over more than 10 days under blue-light irradiation (light-emitting diode centered at 450 nm). A maximum turnover number of 764 was obtained after 12 days.