Raman spectroscopy of electronic excited organometallic complexes: a comparison of the metal to 2,2'-bipyridine charge-transfer state of fac-(2,2'-bipyridine)tricarbonylhalorhenium and tris(2,2'-bipyridine)ruthenium(II)

Abstract

The Raman spectrum of the lowest electronic excited state of R~( b p y ) ,~+ (bpy = 2,2'-bipyridine) shows features that have been attributed to the reduced character of 2,2'-bipyridine in the excited species.'S2 Significantly, near coincidence in the frequency of Raman bands for the excited complex and the ground state 2,2'-bipyridine radical anion is observed,'s2 suggesting that the excited state, which is associated with a metal-to-ligand chargetransfer transition in ab~orption,~ can be viewed as having the (1) (a) Dallinger, R. F.; Woodruff, W. H. J. Am. Chem. SOC. 1979, 101, 4391. (b) Bradley, P. G.; Kress, N.; Hornberger, B. A,; Dallinger, R. F.; Woodruff, W. H. Ibid. 1981, 103, 7441 and references cited therein. (2) Forster, M.; Hester, R. E. Chem. Phys. Lett. 1981, 81, 42. for grant support to M.S.W. and for support of the MIT Regional Laser Facility. Synthesis of fac-XRe(CO),(bpy) by David P. Summers is gratefully acknowledged. Registry No.fac-C1Re(CO)3(bpy), 55658-96-3;fac-BrRe(CO),(bpy), 40231-87-6; Ru(bpy),,+, 15158-62-0. (8) The near-UV absorption spectrum of excited Ru(bpy)32+ closely resembles that of the radical anion of 2,2'-bipyridine; see: Creutz, C.; Chou, M.; Netzel, T. L.; Okumura, M.; Sutin, N.

Understanding excited-state structure in metal polypyridyl complexes using resonance Raman excitation profiles, time-resolved resonance Raman spectroscopy and density functional theory

“…This would not be seen if the excited electron was delocalised across all three bipyridines. Similar characteristic peaks were found for bipyridine complexes of other metals [10,125]. A more recent experiment by Henry and coworkers [116] has examined the vibrational activity of [Ru(bpy) 3 ] 2+ just after photoexcitation with TR 3 spectroscopy.…”

Localized 3MLCT Transitions in [Ru(bpy)3-x(bpy-6,6‘-d2)x]2+ (x = 0−3, bpy = 2,2‘-Bipyridine). Probing Minimally Perturbed Chromophores

“…[2][3][4][5][6][7][8] This result provides an upper limit of ∼200 cm -1 for the excitation exchange interaction between metal-ligand subunits. The effects of any interaction are diminished by the nanoheterogeneity of the ligands.…”

“…A considerable amount of work has been devoted to the question of whether the transferred charge in the lowest-excited 3 MLCT states in [Ru(bpy) 3 ] 2+ is localized on one ligand or delocalized over all three ligands (see ref 1 and refs 1-6 therein).…”

“…The effects of any interaction are diminished by the nanoheterogeneity of the ligands. 1 We have shown by a wide range of experiments such as specific deuteration, [9][10][11] MCPL 12 and Zeeman experiments, 13,14 Stark measurements, 13,15 luminescence and excitation linenarrowing techniques, 10,[16][17][18][19] spectral hole-burning experiments, 16 and the spectroscopy of the series [Ru(bpy) 3-x (phen) x ] 2+ (x ) 0-3, phen ) 1,10-phenanthroline) 19 in [Zn(bpy) 3 ](ClO 4 ) 2 that the lowest-excited 3 MLCT states are also localized in welldefined crystalline systems. For example, independent transitions to the bpy and the phen ligands (as identified from their characteristic splittings) are observed in the spectra of the complexes [Ru(bpy) 3-x (phen) x ] 2+ with x ) 1, 2.…”

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

“…Indeed, comparison of UV-Vis absorption as well as resonance Raman and IR spectra of reduced and excited states is used to assign and characterize the lowest excited state as MLCT [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. This kind of experiments helped to establish that both reduction and MLCT excitation of [ …”