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

Maria Abrahamsson, Leif Hammarström, Derek A. Tocher, Samik Nag, Dipankar Datta

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

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 diacetyl dihydrazone, and L′ 1:2 is the condensate of L and acetone, are synthesized. From X-ray crystal structures, both are found to contain distorted octahedral RuN6 2+ cores. NMR spectra show that the cations in 1 and 2 possess a C2 axis in solution. They display the expected metal-to-ligand charge transfer ( 1MLCT) band in the 400-500 nm region. Complex 1 is nonemissive at room temperature in solution as well as at 80 K. In contrast, complex 2 gives rise to an appreciable emission upon excitation at 440 nm. The room-temperature emission is centered at 730 nm (λem max) with a quantum yield (Φem) of 0.002 and a lifetime (τem) of 42 ns in an air-equilibrated methanol-ethanol solution. At 80 K, Φem = 0.007 and τem = 178 ns, with a λem max 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 temperature and 80 K is almost temperature independent. From spectroelectrochemistry, it is found that bpy is easiest to reduce in 2 and that L is easiest in 1. The implications of this are that in 2 the lowest 3MLCT state is localized on a bpy ligand and in 1 it is localized on L. Transient absorption results also support these assignments. As a consequence, even though 2 shows a fairly strong and long-lived emission from a Ru(II) → bpy CT state, the Ru(II) → L CT state in 1 shows no detectable emission even at 80 K.

Original languageEnglish
Pages (from-to)9580-9586
Number of pages7
JournalInorganic Chemistry
Volume45
Issue number23
DOIs
Publication statusPublished - Nov 13 2006

Fingerprint

azines
Hydrazones
hydrazones
Charge transfer
Metals
charge transfer
Modulation
Ligands
modulation
ligands
metals
room temperature
Spectroelectrochemistry
Diacetyl
Temperature
Quantum yield
Electron transitions
Acetone
Excited states
acetone

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

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. / Abrahamsson, Maria; Hammarström, Leif; Tocher, Derek A.; Nag, Samik; Datta, Dipankar.

In: Inorganic Chemistry, Vol. 45, No. 23, 13.11.2006, p. 9580-9586.

Research output: Contribution to journalArticle

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title = "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",
abstract = "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 diacetyl dihydrazone, and L′ 1:2 is the condensate of L and acetone, are synthesized. From X-ray crystal structures, both are found to contain distorted octahedral RuN6 2+ cores. NMR spectra show that the cations in 1 and 2 possess a C2 axis in solution. They display the expected metal-to-ligand charge transfer ( 1MLCT) band in the 400-500 nm region. Complex 1 is nonemissive at room temperature in solution as well as at 80 K. In contrast, complex 2 gives rise to an appreciable emission upon excitation at 440 nm. The room-temperature emission is centered at 730 nm (λem max) with a quantum yield (Φem) of 0.002 and a lifetime (τem) of 42 ns in an air-equilibrated methanol-ethanol solution. At 80 K, Φem = 0.007 and τem = 178 ns, with a λem max 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 temperature and 80 K is almost temperature independent. From spectroelectrochemistry, it is found that bpy is easiest to reduce in 2 and that L is easiest in 1. The implications of this are that in 2 the lowest 3MLCT state is localized on a bpy ligand and in 1 it is localized on L. Transient absorption results also support these assignments. As a consequence, even though 2 shows a fairly strong and long-lived emission from a Ru(II) → bpy CT state, the Ru(II) → L CT state in 1 shows no detectable emission even at 80 K.",
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AU - Abrahamsson, Maria

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AU - Nag, Samik

AU - Datta, Dipankar

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AB - 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 diacetyl dihydrazone, and L′ 1:2 is the condensate of L and acetone, are synthesized. From X-ray crystal structures, both are found to contain distorted octahedral RuN6 2+ cores. NMR spectra show that the cations in 1 and 2 possess a C2 axis in solution. They display the expected metal-to-ligand charge transfer ( 1MLCT) band in the 400-500 nm region. Complex 1 is nonemissive at room temperature in solution as well as at 80 K. In contrast, complex 2 gives rise to an appreciable emission upon excitation at 440 nm. The room-temperature emission is centered at 730 nm (λem max) with a quantum yield (Φem) of 0.002 and a lifetime (τem) of 42 ns in an air-equilibrated methanol-ethanol solution. At 80 K, Φem = 0.007 and τem = 178 ns, with a λem max 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 temperature and 80 K is almost temperature independent. From spectroelectrochemistry, it is found that bpy is easiest to reduce in 2 and that L is easiest in 1. The implications of this are that in 2 the lowest 3MLCT state is localized on a bpy ligand and in 1 it is localized on L. Transient absorption results also support these assignments. As a consequence, even though 2 shows a fairly strong and long-lived emission from a Ru(II) → bpy CT state, the Ru(II) → L CT state in 1 shows no detectable emission even at 80 K.

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