Modulation of the Lowest Metal-to-Ligand Charge-Transfer State in [Ru(bpy)2(N-N)]2+ Systems by Changing the N-N from Hydrazone to Azine: Photophysical Consequences
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- 作者：Maria Abrahamsson ; Leif Hammarströ ; m ; Derek A. Tocher ; Samik Nag ; Dipankar Datta
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：November 13, 2006
- 年：2006
- 卷：45
- 期：23
- 页码：9580 - 9586
- 全文大小：157K
- 年卷期：v.45,no.23(November 13, 2006)
- ISSN：1520-510X
文摘
Two Ru(II) complexes, [Ru(bpy)2L](ClO4)2 (1) and [Ru(bpy)2L'](BF4)2 (2), where bpy is 2,2'-bipyridine, L is diacetyldihydrazone, and L' 1:2 is the condensate of L and acetone, are synthesized. From X-ray crystal structures, bothare found to contain distorted octahedral RuN62+ cores. NMR spectra show that the cations in 1 and 2 possess aC2 axis in solution. They display the expected metal-to-ligand charge transfer (1MLCT) band in the 400-500 nmregion. Complex 1 is nonemissive at room temperature in solution as well as at 80 K. In contrast, complex 2 givesrise to an appreciable emission upon excitation at 440 nm. The room-temperature emission is centered at 730 nm(
emmax) with a quantum yield (
em) of 0.002 and a lifetime (
em) of 42 ns in an air-equilibrated methanol-ethanolsolution. At 80 K, em = 0.007 and em = 178 ns, with a emmax of 690 nm, which is close to the 0-0 transition,indicating an 3MLCT excited-state energy of 1.80 eV. The radiative rate constant (5 × 104 s-1) at room temperatureand 80 K is almost temperature independent. From spectroelectrochemistry, it is found that bpy is easiest toreduce in 2 and that L is easiest in 1. The implications of this are that in 2 the lowest 3MLCT state is localized ona bpy ligand and in 1 it is localized on L. Transient absorption results also support these assignments. As aconsequence, even though 2 shows a fairly strong and long-lived emission from a Ru(II) 
bpy CT state, theRu(II) L CT state in 1 shows no detectable emission even at 80 K.
emmax) with a quantum yield (em) of 0.002 and a lifetime (em) of 42 ns in an air-equilibrated methanol-ethanolsolution. At 80 K, em = 0.007 and em = 178 ns, with a emmax of 690 nm, which is close to the 0-0 transition,indicating an 3MLCT excited-state energy of 1.80 eV. The radiative rate constant (5 × 104 s-1) at room temperatureand 80 K is almost temperature independent. From spectroelectrochemistry, it is found that bpy is easiest toreduce in 2 and that L is easiest in 1. The implications of this are that in 2 the lowest 3MLCT state is localized ona bpy ligand and in 1 it is localized on L. Transient absorption results also support these assignments. As aconsequence, even though 2 shows a fairly strong and long-lived emission from a Ru(II) bpy CT state, theRu(II) L CT state in 1 shows no detectable emission even at 80 K.