Abstract
Absorption and emission spectra, emission quantum yields, and excited-state lifetimes of the metal-to-ligand charge-transfer (MLCT) excited state(s) of Ru(bpy)2(6-Mebpy)2+, Ru(bpy)2(bpy-cyclamH2)4+, and Ru(bpy)2(bpy-cyclamNi)4+ are reported. The absorption and emission spectra of these complexes are similar to those of Ru(bpy)3 2+ in H2O at room temperature except for small shifts in the maxima. The emission lifetime decreases by a factor of about 80 for 6-Mebpy, and the emission quantum yield decreases by a factor of about 300 for the bpy-cyclam pendant complexes as compared to the parent Ru(bpy)3 2+ complex at 25 °C. Decay of the 3MLCT excited state takes place by two independent channels: a temperature-independent pathway to the ground state and a thermally-activated pathway via a ligand-field excited state. Activation free energies, Ea, for the latter pathway were obtained from fits of the temperature-dependent emission lifetime measurements. Smaller Ea were observed for the 6-substituted complexes (1500-2300 cm-1) relative to Ru(bpy)3 2+ (3000-3910 cm-1) in EtOH and CH3CN, indicating that either the energy difference decreases and/or the reorganization parameter changes between the emissive 3MLCT and the ligand-field state to which it is strongly coupled. The smaller Ea can be attributed to the increased Ru-N bond distance in the 6-substituted complexes caused by steric hindrance that decreases the ligand-field strength and lowers the energy and/or reorganization parameter of the ligand-field excited state. For the bpy-cyclamNi2+ pendant complex, an energy-transfer pathway may also provide a deactivation channel.
| Original language | English |
|---|---|
| Pages (from-to) | 2079-2085 |
| Number of pages | 7 |
| Journal | Inorganic Chemistry |
| Volume | 31 |
| Issue number | 11 |
| Publication status | Published - 1992 |
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- Inorganic Chemistry
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Photophysical properties of covalently attached Ru(bpy)3 2+ and mcyclam2+ (M = Ni, H2) complexes. / Fujita, Etsuko; Milder, Steven J.; Brunschwig, Bruce S.
In: Inorganic Chemistry, Vol. 31, No. 11, 1992, p. 2079-2085.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Photophysical properties of covalently attached Ru(bpy)3 2+ and mcyclam2+ (M = Ni, H2) complexes
AU - Fujita, Etsuko
AU - Milder, Steven J.
AU - Brunschwig, Bruce S.
PY - 1992
Y1 - 1992
N2 - Absorption and emission spectra, emission quantum yields, and excited-state lifetimes of the metal-to-ligand charge-transfer (MLCT) excited state(s) of Ru(bpy)2(6-Mebpy)2+, Ru(bpy)2(bpy-cyclamH2)4+, and Ru(bpy)2(bpy-cyclamNi)4+ are reported. The absorption and emission spectra of these complexes are similar to those of Ru(bpy)3 2+ in H2O at room temperature except for small shifts in the maxima. The emission lifetime decreases by a factor of about 80 for 6-Mebpy, and the emission quantum yield decreases by a factor of about 300 for the bpy-cyclam pendant complexes as compared to the parent Ru(bpy)3 2+ complex at 25 °C. Decay of the 3MLCT excited state takes place by two independent channels: a temperature-independent pathway to the ground state and a thermally-activated pathway via a ligand-field excited state. Activation free energies, Ea, for the latter pathway were obtained from fits of the temperature-dependent emission lifetime measurements. Smaller Ea were observed for the 6-substituted complexes (1500-2300 cm-1) relative to Ru(bpy)3 2+ (3000-3910 cm-1) in EtOH and CH3CN, indicating that either the energy difference decreases and/or the reorganization parameter changes between the emissive 3MLCT and the ligand-field state to which it is strongly coupled. The smaller Ea can be attributed to the increased Ru-N bond distance in the 6-substituted complexes caused by steric hindrance that decreases the ligand-field strength and lowers the energy and/or reorganization parameter of the ligand-field excited state. For the bpy-cyclamNi2+ pendant complex, an energy-transfer pathway may also provide a deactivation channel.
AB - Absorption and emission spectra, emission quantum yields, and excited-state lifetimes of the metal-to-ligand charge-transfer (MLCT) excited state(s) of Ru(bpy)2(6-Mebpy)2+, Ru(bpy)2(bpy-cyclamH2)4+, and Ru(bpy)2(bpy-cyclamNi)4+ are reported. The absorption and emission spectra of these complexes are similar to those of Ru(bpy)3 2+ in H2O at room temperature except for small shifts in the maxima. The emission lifetime decreases by a factor of about 80 for 6-Mebpy, and the emission quantum yield decreases by a factor of about 300 for the bpy-cyclam pendant complexes as compared to the parent Ru(bpy)3 2+ complex at 25 °C. Decay of the 3MLCT excited state takes place by two independent channels: a temperature-independent pathway to the ground state and a thermally-activated pathway via a ligand-field excited state. Activation free energies, Ea, for the latter pathway were obtained from fits of the temperature-dependent emission lifetime measurements. Smaller Ea were observed for the 6-substituted complexes (1500-2300 cm-1) relative to Ru(bpy)3 2+ (3000-3910 cm-1) in EtOH and CH3CN, indicating that either the energy difference decreases and/or the reorganization parameter changes between the emissive 3MLCT and the ligand-field state to which it is strongly coupled. The smaller Ea can be attributed to the increased Ru-N bond distance in the 6-substituted complexes caused by steric hindrance that decreases the ligand-field strength and lowers the energy and/or reorganization parameter of the ligand-field excited state. For the bpy-cyclamNi2+ pendant complex, an energy-transfer pathway may also provide a deactivation channel.
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M3 - Article
VL - 31
SP - 2079
EP - 2085
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 11
ER -