Trinuclear Ru(II)‐Ru(II)‐Ru(II) Complexes as Efficient Photosensitizers for Potent Aqueous Singlet Oxygen Generation and NADH Photo‐Oxidation

Here, two new tripodal polypyridyl Ru(II) complexes [(DIP)6Ru3L]6+ (D-3Ru) and [(Phen)6Ru3L]6+ (P-3Ru) (L = 4,4'-bis(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-2,2'-bipyridine), as new photosensitizers were developed and fully characterized by 1H/13C NMR, HRMS and elemental analysis. The electrochemical cyclic voltammetry study, and density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were determined to investigate the electronic properties. Both complexes showed strong fluorescence in various solutions, with emission lifetimes of 305 ns (D-3Ru) and 291 ns (D-3Ru). D-3Ru generated high amount of singlet oxygen under low-power light exposure (blue (465 nm) and red (650 nm) LED lights), with singlet oxygen quantum yields (ΦΔ) of 1.86 (acetonitrile) and 2.13 (PBS) in comparison to that of [Ru(bpy)3]Cl2, and such potency was also confirmed by oxidation of 1,5-dihydroxynaphthalene (DHN). D-3Ru also generated superoxide and hydroxyl radicals with high reaction efficiency under blue LED light irradiation, and could oxidize coenzyme NADH with powerful reaction rate, giving a turnover frequency (TOF) value high as 5820 h-1. The current work provides new example of trinuclear Ru(II) complexes as competent type I and II photosensitizer candidates.