Abstract
For the structurally rigid homometallic dinuclear complexes (ttp)Ru(tpy-tpy)Ru(ttp)4+ and (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, we have obtained ground-state absorption spectra and transient-absorption difference spectra at room temperature and luminescence spectra and lifetimes in the temperature interval from room temperature to the rigid matrix (90 K); the solvent was acetonitrile or butyronitrile (tpy is 2,27prime;:6′,2″-terpyridine, ttp is 4′-p-tolyl-2,2′:6′,2″-tpy, and ph is 1,4-phenylene). The gathered spectroscopic data indicate that after absorption of visible light, formation of the luminescent metal-to-ligand charge transfer (MLCT) excited states takes place, which involves the bridging ligand (BL). Since we found that (ttp)Ru(tpy-tpy)Ru(ttp)4+ is a good luminophore (λmax = 720 nm, Φ = 4.7 x 10-3, and τ = 570 ns) while both (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+ (λmax = 656 nm, Φ = 1.1 x 10-4, and τ = 4 ns) and the reference mononuclear complex Ru(ttp)2 2+ (λmax = 640 nm, Φ = 3.2 x 10-5, and τ = 0.9 ns) are not, we have explored the effects brought about by the delocalization and energy content of the luminescent state. The study of the temperature dependence of the luminescence lifetimes indicates that two main nonradiative paths, i and ii, are responsible for deactivation of the luminescent state. Path i directly connects the luminescent and ground states; within the frame of the "energy-gap law", vibronic analysis of low-temperature luminescence profiles enables one to correlate the delocalization of the M → BL CT state and the extent of structural distortions occurring at the accepting ligand. Thermally activated decay via a metal-centered (MC, of dd orbital origin) excited state characterizes path ii, with a MLCT - MC energy separation ΔE = 3800, 2300, and 1600 cm-1 for (ttp)Ru(tpy-tpy)Ru-(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(ttp)2 2+, respectively. At room temperature, for this limited series of complexes it is found that nonradiative processes governed by the "energy-gap law" play a minor role as compared to thermally activated processes, the ratios of the rate constants being knr act/knr dir ≈ 16, 1900, and 7000 for (ttp)Ru(tpy-tpy)Ru(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(Up)2 2+, respectively.
| Original language | English |
|---|---|
| Pages (from-to) | 9061-9069 |
| Number of pages | 9 |
| Journal | Journal of Physical Chemistry A |
| Volume | 101 |
| Issue number | 48 |
| Publication status | Published - Nov 27 1997 |
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- Physical and Theoretical Chemistry
Cite this
A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II). / Hammarström, Leif; Barigelletti, Francesco; Flamigni, Lucia; Indelli, Maria Teresa; Armaroli, Nicola; Calogero, Giuseppe; Guardigli, Massimo; Sour, Angelique; Collin, Jean Paul; Sauvage, Jean Pierre.
In: Journal of Physical Chemistry A, Vol. 101, No. 48, 27.11.1997, p. 9061-9069.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II)
AU - Hammarström, Leif
AU - Barigelletti, Francesco
AU - Flamigni, Lucia
AU - Indelli, Maria Teresa
AU - Armaroli, Nicola
AU - Calogero, Giuseppe
AU - Guardigli, Massimo
AU - Sour, Angelique
AU - Collin, Jean Paul
AU - Sauvage, Jean Pierre
PY - 1997/11/27
Y1 - 1997/11/27
N2 - For the structurally rigid homometallic dinuclear complexes (ttp)Ru(tpy-tpy)Ru(ttp)4+ and (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, we have obtained ground-state absorption spectra and transient-absorption difference spectra at room temperature and luminescence spectra and lifetimes in the temperature interval from room temperature to the rigid matrix (90 K); the solvent was acetonitrile or butyronitrile (tpy is 2,27prime;:6′,2″-terpyridine, ttp is 4′-p-tolyl-2,2′:6′,2″-tpy, and ph is 1,4-phenylene). The gathered spectroscopic data indicate that after absorption of visible light, formation of the luminescent metal-to-ligand charge transfer (MLCT) excited states takes place, which involves the bridging ligand (BL). Since we found that (ttp)Ru(tpy-tpy)Ru(ttp)4+ is a good luminophore (λmax = 720 nm, Φ = 4.7 x 10-3, and τ = 570 ns) while both (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+ (λmax = 656 nm, Φ = 1.1 x 10-4, and τ = 4 ns) and the reference mononuclear complex Ru(ttp)2 2+ (λmax = 640 nm, Φ = 3.2 x 10-5, and τ = 0.9 ns) are not, we have explored the effects brought about by the delocalization and energy content of the luminescent state. The study of the temperature dependence of the luminescence lifetimes indicates that two main nonradiative paths, i and ii, are responsible for deactivation of the luminescent state. Path i directly connects the luminescent and ground states; within the frame of the "energy-gap law", vibronic analysis of low-temperature luminescence profiles enables one to correlate the delocalization of the M → BL CT state and the extent of structural distortions occurring at the accepting ligand. Thermally activated decay via a metal-centered (MC, of dd orbital origin) excited state characterizes path ii, with a MLCT - MC energy separation ΔE = 3800, 2300, and 1600 cm-1 for (ttp)Ru(tpy-tpy)Ru-(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(ttp)2 2+, respectively. At room temperature, for this limited series of complexes it is found that nonradiative processes governed by the "energy-gap law" play a minor role as compared to thermally activated processes, the ratios of the rate constants being knr act/knr dir ≈ 16, 1900, and 7000 for (ttp)Ru(tpy-tpy)Ru(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(Up)2 2+, respectively.
AB - For the structurally rigid homometallic dinuclear complexes (ttp)Ru(tpy-tpy)Ru(ttp)4+ and (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, we have obtained ground-state absorption spectra and transient-absorption difference spectra at room temperature and luminescence spectra and lifetimes in the temperature interval from room temperature to the rigid matrix (90 K); the solvent was acetonitrile or butyronitrile (tpy is 2,27prime;:6′,2″-terpyridine, ttp is 4′-p-tolyl-2,2′:6′,2″-tpy, and ph is 1,4-phenylene). The gathered spectroscopic data indicate that after absorption of visible light, formation of the luminescent metal-to-ligand charge transfer (MLCT) excited states takes place, which involves the bridging ligand (BL). Since we found that (ttp)Ru(tpy-tpy)Ru(ttp)4+ is a good luminophore (λmax = 720 nm, Φ = 4.7 x 10-3, and τ = 570 ns) while both (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+ (λmax = 656 nm, Φ = 1.1 x 10-4, and τ = 4 ns) and the reference mononuclear complex Ru(ttp)2 2+ (λmax = 640 nm, Φ = 3.2 x 10-5, and τ = 0.9 ns) are not, we have explored the effects brought about by the delocalization and energy content of the luminescent state. The study of the temperature dependence of the luminescence lifetimes indicates that two main nonradiative paths, i and ii, are responsible for deactivation of the luminescent state. Path i directly connects the luminescent and ground states; within the frame of the "energy-gap law", vibronic analysis of low-temperature luminescence profiles enables one to correlate the delocalization of the M → BL CT state and the extent of structural distortions occurring at the accepting ligand. Thermally activated decay via a metal-centered (MC, of dd orbital origin) excited state characterizes path ii, with a MLCT - MC energy separation ΔE = 3800, 2300, and 1600 cm-1 for (ttp)Ru(tpy-tpy)Ru-(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(ttp)2 2+, respectively. At room temperature, for this limited series of complexes it is found that nonradiative processes governed by the "energy-gap law" play a minor role as compared to thermally activated processes, the ratios of the rate constants being knr act/knr dir ≈ 16, 1900, and 7000 for (ttp)Ru(tpy-tpy)Ru(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(Up)2 2+, respectively.
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M3 - Article
VL - 101
SP - 9061
EP - 9069
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
SN - 1089-5639
IS - 48
ER -