Tuning the Electronics of Bis(tridentate)ruthenium(II) Complexes with Long-Lived Excited States: Modifications to the Ligand Skeleton beyond Classical Electron Donor or Electron Withdrawing Group Deco

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• 作者：Giovanny A. Parada ; Lisa A. Fredin ; Marie-Pierre Santoni ; Michael J盲ger ; Reiner Lomoth ; Leif Hammarstr枚m ; Olof Johansson ; Petter Persson ; Sascha Ott
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：May 6, 2013
• 年：2013
• 卷：52
• 期：9
• 页码：5128-5137
• 全文大小：457K
• 年卷期：v.52,no.9(May 6, 2013)
• ISSN：1520-510X

文摘

A series of homoleptic bis(tridentate) [Ru(L)b>2b>]²⁺ (<b>1b>, <b>3b>) and heteroleptic [Ru(L)(dqp)]²⁺ complexes (<b>2b>, <b>4b>) [L = dqxp (<b>1b>, <b>2b>) or dNinp (<b>3b>, <b>4b>); dqxp = 2,6-di(quinoxalin-5-yl)pyridine, dNinp = 2,6-di(N-7-azaindol-1-yl)pyridine, dqp = 2,6-di(quinolin-8-yl)pyridine] was prepared and in the case of <b>2b> and <b>4b> structurally characterized. The presence of dqxp and dNinp in <b>1b>鈥?b>4b> result in anodically shifted oxidation potentials of the Ru^3+/2+ couple compared to that of the archetypical [Ru(dqp)b>2b>]²⁺ (<b>5b>), most pronounced for [Ru(dqxp)b>2b>]²⁺ (<b>1b>) with a shift of +470 mV. These experimental findings are corroborated by DFT calculations, which show contributions to the complexes鈥?HOMOs by the polypyridine ligands, thereby stabilizing the HOMOs and impeding electron extraction. Complex <b>3b> exhibits an unusual electronic absorption spectrum with its lowest energy maximum at 382 nm. TD-DFT calculations suggest that this high-energy transition is caused by a localization of the LUMO on the central pyridine fragments of the dNinp ligands in <b>3b>, leaving the lateral azaindole units merely spectator fragments. The opposite is the case in <b>1b>, where the LUMO experiences large stabilization by the lateral quinoxalines. Owing to the differences in LUMO energies, the complexes鈥?reduction potentials differ by about 900 mV [Eb>1/2b>(<b>1b>^2+/1+) = 鈭?.17 V, Eb>c,pb>(<b>3b>^2+/1+) = 鈭?.06 V vs Fc^+/0]. As complexes <b>1b>鈥?b>4b> exhibit similar excited state energies of around 1.80 V, the variations of the lateral heterocycles allow the tuning of the complexes鈥?excited state oxidation strengths over a range of 900 mV. Complex <b>1b> is the strongest excited state oxidant of the series, exceeding even [Ru(bpy)b>3b>]²⁺ by more than 200 mV. At room temperature, complex <b>3b> is nonemissive, whereas complexes <b>1b>, <b>2b>, and <b>4b> exhibit excited state lifetimes of 255, 120, and 1570 ns, respectively. The excited state lifetimes are thus somewhat shortened compared to that of <b>5b> (3000 ns) but still acceptable to qualify the complexes as photosensitizers in light-induced charge-transfer schemes, especially for those that require high oxidative power.