TY - JOUR A1 - Kreitner, C. A1 - Grabolle, Markus A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - Dual emission and excited-state mixed-valence in a quasi-symmetric dinuclear Ru-Ru complex JF - Inorganic Chemistry N2 - The synthesis and characterization of the new dinuclear dipeptide [(EtOOC-tpy)Ru(tpy-NHCO-tpy)Ru(tpy-NHCOCH3)]4+ 34+ of the bis(terpyridine)ruthenium amino acid [(HOOC-tpy)Ru(tpy-NH2)]2+ 12+ are described, and the properties of the dipeptide are compared to those of the mononuclear complex [(EtOOC-tpy)Ru(tpy-NHCOCH3)]2+ 42+ carrying the same functional groups. 34+ is designed to serve a high electronic similarity of the two ruthenium sites despite the intrinsic asymmetry arising from the amide bridge. This is confirmed via UV–vis absorption and NMR spectroscopy as well as cyclic voltammetry. 42+ and 34+ are emissive at room temperature, as expected. Moreover, 34+ exhibits dual emission from two different triplet states with different energies and lifetimes at room temperature. This is ascribed to the presence of a unique thermal equilibrium between coexisting [RuII(tpy-NHCO-tpy·–)RuIII] and [RuIII(tpy-NHCO-tpy·–)RuII] states leading to an unprecedented excited-state RuIIRuIII mixed-valent system via the radical anion bridge tpy-NHCO-tpy·–. The mixed-valent cation 35+, on the other hand, shows no measurable interaction of the RuIIRuIII centers via the neutral bridge tpy-NHCO-tpy (Robin–Day class I). Reduction of 34+ to the radical cation 33+ by decamethylcobaltocene is bridge-centered as evidenced by rapid-freeze electron paramagnetic resonance spectroscopy. Interestingly, all attempts to observe 33+ via NMR and UV–vis absorption spectroscopy only led to the detection of the diamagnetic complex 3-H3+ in which the bridging amide is deprotonated. Hence 3-H3+ (and 4-H+) appear to reduce protons to dihydrogen. The ease of single and double deprotonation of 42+ and 34+ to 4-H+, 3-H3+, and 3-2H2+ was demonstrated using a strong base and was studied using NMR and UV–vis absorption spectroscopies. The equilibrating excited triplet states of 34+ are reductively quenched by N,N-dimethylaniline assisted by hydrogen bonding to the bridging amide. KW - Dual emission KW - Excited state mixed-valence KW - Electron transfer KW - Ruthenium KW - Terpyridine KW - Amide acidity PY - 2014 DO - https://doi.org/10.1021/ic5020362 SN - 0020-1669 SN - 1520-510X VL - 53 IS - 24 SP - 12947 EP - 12961 PB - American Chemical Society CY - Washington, DC AN - OPUS4-32536 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -