| Since the report of the DNA "light-switch" prototype [Ru(bpy) 2(dppz)]2+ (2,2&feet;-bipyridine, dppz = dipyrido[3,2- a:2&feet;,3&feet;-c]phenazine), which is nonemissive in aqueous solutions but highly emissive upon addition of DNA, a large number of [Ru(bpy)2L]2+ (L = dppz derivative) complexes have been reported. The DNA "light-switch" performance of six [Ru(bpy)2L]2+ complexes, where L = bpy, dppz, dppx (7,8-dimethyldipyrido[3,2-a:2&feet;,3&feet;-c]phenazine), dppm2 (6-methyldipyrido[3,2-a:2&feet;,3&feet;-c]phenazine), tpphz (tetrapyrido[3,2-a:2&feet;,3&feet;-c:3&feet;&feet;,2&feet;&feet;- h:2&feet;&feet;&feet;,3&feet;&feet;&feet;-j]phenazine), and dppp2 (pyrido[2&feet;,3&feet;:5,6]pyrazino[2,3-f][1,10]phenanthroline), is compared in the present work and their differences are understood following the use of various techniques, including steady-state and time-resolved spectroscopy, electrochemistry, and electronic structure calculations. The solvent dependence of the emission of [Ru(bpy)n(dppp2)3-n]2+ (n = 0 -- 2) reveals that the stabilization of the lowest energy 3MLCT (metal-to-ligand charge transfer) state in these complexes is highly dependent on solvent polarity.;Inspired by the structural similarity but strikingly different photophysical properties between [Ru(bpy)2(dppz)]2+ and [Ru(bpy) 2(dppp2)]2+, a new Ru(II) polypyridyl complex, [Ru(bpy) 2(dpqp)]2+ (dpqp = pyrazino[2&feet;,3&feet;:5,6]pyrazino[2,3- f][1,10]phenanthroline), was designed and investigated. Unlike [Ru(bpy) 2L]2+ complexes (L = dppz derivative), which are typically nonemissive or weakly emissive in aqueous media, [Ru(bpy)2(dpqp)] 2+ shows intense luminescence in water at room temperature. The dependence of its luminescence on pH yields an apparent pKa* of 2.1.;The photophysical and photochemical properties of various Ru(II) and Os(II) polypyridyl complexes with potential application in photodynamic therapy (PDT) were also investigated. [Ru(bpy)2(dppn)]2+ (dppn = benzo[i]dipyrido[3,2-a:2&feet;,3&feet;-c ]phenazine) is able to achieve nearly complete DNA cleavage under irradiation of visible light (lambdairr ≥ 455 nm) for only 30 s. Further studies concluded that the population and reactivity of two low-lying excited states, a weakly emissive 3MLCT state and a long-lived dppn-centered 3pipi* state, lead to this remarkably efficient DNA photocleavage. Considering the depth of light penetration of human tissue, we designed and synthesized a new osmium complex, [Os(bpy) 2(dppn)]2+, which is able to cleave DNA under irradiation in the PDT window (650 -- 850 nm).;Six ruthenium complexes with tridentate ligands, [Ru(tpy)nL 2-n]2+ (n = 0, 1, 2), where tpy = [2,2&feet;;6&feet;,2&feet;&feet;]-terpyridine and L = pydppx (3-(pyrid-2&feet;-yl)-11,12-dimethyldipyrido[3,2-a :2&feet;,3&feet;-c]phenazine), pydppn (3-(pyrid-2&feet;-yl)-4,5,9,16-tetraaza-dibenzo[ a,c]naphthacene), and [Ru(tpy)(pydbn)]+ (pydbn - represents deprotonated pyHdbn = 3-pyrid-2&feet;-yl-4,9,16-triaza-dibenzo[ a,c]naphthacene), were also investigated. Although the extended pi-system of pydbn- is similar to that of pydppn, the negative charge on pydbn- has a substantial effect on its electronic configuration. The lowest triplet excited state of [Ru(tpy)(pydbn)]+ is a combination of 3MLCT and 3pipi* in character, resulting in absence of luminescence and long-lived 3pipi* state.;Inspired by the success of cisplatin (cis-Pt(NH3)2Cl 2) as an antitumor agent, the photoaquation of a number of Ru(II) and Os(II) complexes as cisplatin analogs was investigated. These complexes include [Ru(bpy)2L2]2+ (L = NH3, pyridine, and CH3CN) and [Os(bpy)2(CH3CN)2] 2+, with the aim of designing oxygen-independent PDT agents. [Ru(bpy) 2(CH3CN)2]2+ was found to possess a significantly greater quantum yield of photoaquation than [Ru(bpy) 2L2]2+ (L = NH3 and pyridine) and [Os(bpy)2(CH3CN)2]2+. The greater photoaquation quantum yield of [Ru(bpy)2(CH3CN) 2]2+ can be attributed to its smallest 3LF- 3MLCT gap and largest geometric distortion of the lowest-lying excited state. Further experiments demonstrate that [Ru(bpy)2(CH3 CN)2]2+ is able to covalently bind to DNA under visible light irradiation, a process that is independent of oxygen. |
