Photoinduced energy- and electron-transfer processes in dinuclear ruthenium(II) and/or osmium(II) complexes connected by a linear rigid bis-chelating bridge
✍ Scribed by Luisa de Cola; Vincenzo Balzani; Francesco Barigelletti; Lucia Flamigni; Peter Belser; Stefan Bernhard
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 835 KB
- Volume
- 114
- Category
- Article
- ISSN
- 0165-0513
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
A rigid and linear bridging ligand containing two 4,5‐diazafluorene chelating units separated by an adamantane spacer (diazf‐a‐diazf) has been synthesized and its dinuclear complexes [(bpy)~2~Ru(diazf‐a‐diazf)Ru(bpy)~2~]^4+^ (Ru^II^ · FAF · Ru^II^), [(bpy)~2~Os(diazf‐a‐diazf)Os(bpy)~2~]^4+^ (Os^II^ · FAF · Os^II^), and [(bpy)~2~Ru(diazf‐a‐diazf)Os(bpy)~2~]^4+^ (Ru^II^ · FAF · Os^II^) have been prepared as PF^−^~6~ salts. In these novel compounds, each Ru‐based and Os‐based unit displays its own absorption spectrum and electrochemical properties, regardless of the presence of a second metal‐based unit. The luminescence properties have also been investigated and it has been shown that electronic energy transfer takes place in the mixed‐metal Ru^II^ · FAF · Os^II^ species at 77K from the Ru‐based to the Os‐based unit with rate constant 2.6 · 10^8^ s^−1^. At room temperature the intrinsic decay of the Ru‐based unit is too fast (3.3 · 10^9^ s^−1^) to allow the occurrence of energy transfer. Partial oxidation of the binuclear compounds Ru^II^ · FAF · Os^II^ and Os^II^ · FAF · Os^II^ by Ce^IV^ in acetonitrile‐water solutions leads to the mixed‐valence Ru^II^ · FAF · Os^III^ and Os^II^ · FAF · Os^III^ species where the oxidized metal‐based unit quenches, by electron transfer, the luminescent excited state of the unit that is not oxidized. At room temperature, the rate constants for the excited state * Ru^II^ · FAF · Os^III^ · Ru^III^ · FAF · Os^II^ and * Os^II^ FAF · Os^III^ · Os^III^ · FAF · Os^II^ processes are 8.3 · 10^8^ s^−1^ and 3.9 · 10^8^ s^−1^, respectively, and the rate constant for the back‐electron‐transfer process Ru^III^ · FAF · Os^II^ · Ru^II^ · FAF · Os^III^ is 2.9 · 10^7^ s^−1^.