Excited-state absorption spectroscopy and spectroelectrochemistry of tetrakis(2,2'-bipyridine)(.mu.-2,3-bis(2-pyridyl)pyrazine)diruthenium(II) and its mononuclear counterpart: a comparative study

Abstract

Excited-state absorption spectra of the complexes [(bpy)2Ru(dpp)Ru(bpy)2]4+ and [Ru(bpy)2(dpp)]2+ (bpy = 2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine) in ethanol have been obtained. The excited-state spectra of both complexes exhibit bands in the near-UV region (350 nm for the binuclear complex and 370 nm for the mononuclear complex). In the visible region, a residual metal-to-ligand charge-transfer transition from the remaining Ru(II) center of the binuclear complex to the second lowest r* orbital of the dpp ligand occurs. No comparable band appears in the spectrum of the mononuclear complex. Weak bands also occur in the 610-630-nm region in both complexes. The excited states of the binuclear and mononuclear complex decay with lifetimes of 80 ± 10 and 210 ± 20 ns, respectively, and both complexes emit in room-temperature ethanol solution (0 = 0.0012 ± 0.0003 and 0.011 ± 0.001). Spectroelectrochemistry has been used to characterize the reduced forms of the complexes. The first reduction of each complex occurs at the dpp ligand, and the spectra of these singly reduced complexes resemble the excited-state spectra.There is, however, significantly more absorption in the 450-500-nm region for the reduced complexes, consistent with the presence of one or two Ru(Il) centers capable of engaging in MLCT transitions. The second reduction of the binuclear complex occurs at the dpp ligand, while the second reduction of the mononuclear complex occurs at one of the bpy ligands. introduction Since the first observation* of luminescence from Ru(bpy)32+ (bpy = 2,2'-bipyridine) and the subsequent discovery of its rich Contribution from

Resonance Raman and time‐resolved resonance Raman spectra of the monomeric and dimeric complexes of ruthenium(II) with 2,3‐bis(2‐pyridyl)pyrazine (dpp)

“…Further efforts were made to enhance the dpp ž modes using excitation near 532 nm, which is in a region corresponding to a reported peak in the excited-state absorption spectrum of the dimeric complex. 39,41 However, as can be seen by inspection of traces c and d of Fig. 4, no evidence for excited-state modes was obtained, with the pulsed and cw spectra matching each other fairly closely.…”

Origin of electronic absorption spectra of MLCT-excited and one-electron reduced 2,2′-bipyridine and 1,10-phenanthroline complexes

“…In the case of mixed-ligand complexes, excited-state spectroscopy in combination with spectroelectrochemistry can reveal the localization of the excited electron. For example, observation of dpp ÅÀ (dpp = 2,3-bis(2-pyridyl)pyrazine) UV-Vis features in the excited-state spectrum of a dinuclear complex [(bpy) 2 Ru(l-dpp)Ru(bpy) 2 ] 2+ provided an evidence that MLCT excitation is directed to the bridging ligand instead of bpy [19]. The similarities between UV-Vis spectroscopic effects of reduction and MLCT excitation are less obvious in complexes of 1,10-phenanthroline (phen) such as [Ru(phen) 3 ] 2+ [20] and [W(CO) 4 (phen)] [15].…”

The mononuclear ruthenium(III)-2,3,5,6-tetrakis(2-pyridyl)pyrazine complex [Ru(bpy)(tppz)Cl][PF6]2: synthesis, crystal structure, electrochemical, and spectroelectrochemical studies

“…p* transitions, which are typically seen in the visible region of the spectrum. SEC techniques have been used to elucidate various properties of ruthenium complexes with 2,2 0 -bipyridine ligands [2,[14][15][16][17][18][19]. For instance, electronic absorption SEC measurements were used to confirm electrochemical assignments of [Ru(bpy)(dpp)] 2?…”