Oligomeric dicyanobis(polypyridine)ruthenium(II) complexes. Synthesis, spectroscopic, and photophysical properties
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Abstract
The polychromophoric systems NC-RuII(bpy)2-CN-RuII(bpy)2-CN+(2,2), NC-RuII(bpy)2-CN-RuII(phen)2-CN+(2,2ʹ), and NC-RuII(bpy)2-CN-RuII(bpy)2-NC-RuII(bpy)2-CN2+(2,2,2) have been synthesized. Their redox, spectroscopic, and photophysical properties have been studied and compared with those of the Ru(bpy)2(CN)2and Ru(phen)2(CN)2complexes. In the series Ru(bpy)2(CN)2, (2,2), (2,2,2), Ru(phen)2(CN)2, and (2,2ʹ) the ease of oxidation of the ruthenium atoms increases in the order NC-Ru-CN, CN-Ru-CN, CN-Ru-NC. All the complexes were found to be emitting, with monoexponential decays of the emission intensity at 298 K as well as at 77 K. The energy of the emissions undergoes a bathochromic shift in going from mononuclear to polynuclear species, indicating that the lowest d-π* triplet excited state is on the N-bonded Ru(bpy)22+or Ru(phen)22+chromophoric unit and that intramolecular energy transfer between the C-bonded and N-bonded chromophores is very efficient. The singly oxidized forms of the polynuclear complexes NC-RuII(bpy)2-CN-RuIII(bpy)2-CN2+(2,3), NC-RuII(bpy)2-CN-RuIII(phen)2-CN2+(2,3ʹ), and NC-RuII(bpy)2-CN-RuIII(bpy)2-NC-RuII(bpy)2-CN3+(2,3,2) were electrochemically or chemically generated in D2O solutions. The intense metal-to-metal (RuII→ RuIII) IT transitions observed for the mixed-valence species in the near-infrared region indicate a high degree of electron delocalization relative to that of typical class II mixed-valence compounds. The lack of emission for (2,3), (2,3ʹ), and (2,3,2) is assigned to highly efficient intramolecular electron-transfer quenching processes. © 1989, American Chemical Society. All rights reserved.
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