Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone

Synthesis, characterization, and photoinduced electron transfer reactions

Magnus Borgström, Olof Johansson, Reiner Lomoth, Helena Berglund Baudin, Staffan Wallin, Licheng Sun, Björn Åkermark, Leif Hammarström

Research output: Contribution to journalArticle

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Abstract

Two electron donor-acceptor triads based on a benzoquinone acceptor linked to a light absorbing [Ru(bpy)3]2+ complex have been synthesized. In triad 6 (denoted RuII- BQ-CoIII), a [Co(bpy)3]3+ complex, a potential secondary acceptor, was linked to the quinone. In the other triad, 8 (denoted PTZ-RuII-BQ), a phenothiazine donor was linked to the ruthenium moiety. The corresponding dyads RuII-BQ (4) and PTZ-RuII (9) were prepared for comparison. Upon light excitation in the visible band of the ruthenium moiety, electron transfer to the quinone occurred with a rate constant kf = 5 × 109 s-1f = 200 ps) in all the quinone containing complexes. Recombination to the ground state followed, with a rate constant kb ∼ 4.5 × 108 s-1b ∼ 2.2 ns), for both RuII-BQ and Ru II-BQ-CoIII with no indication of a charge shift to generate the reduced CoII moiety. In the PTZ-RuII-BQ triad, however, the initial charge separation was followed by a rapid (k > 5 × 109 s-1) electron transfer from the phenothiazine moiety to give the fairly long-lived PTZ.+-RuII-BQ .- state (τ = 80 ns) in unusually high yield for a [Ru(bpy) 3]2+-based triad (> 90%), that lies at ΔG° = 1.32 eV relative to the ground state. Unfortunately, this triad turned out to be rather photolabile. Interestingly, coupling between the oxidized PTZ .+ and the BQ.- moieties seemed to occur. This discouraged further extension to incorporate more redox active units. Finally, in the dyad PTZ-RuII a reversible, near isoergonic electron transfer was observed on excitation. Thus, a quasiequilibrium was established with an observed time constant of 7 ns, with ca. 82% of the population in the PTZ-*RuII state and 18% in the PTZ.+-Ru II(bpy.-) state. These states decayed in parallel with an observed lifetime of 90 ns. The initial electron transfer to form the PTZ .+-RuII(bpy.-) state was thus faster than what would have been inferred from the *RuII emission decay (τ = 90 ns). This result suggests that reports for related PTZ-RuII and PTZ-RuII-acceptor complexes in the literature might need to be reconsidered.

Original languageEnglish
Pages (from-to)5173-5184
Number of pages12
JournalInorganic Chemistry
Volume42
Issue number17
DOIs
Publication statusPublished - Aug 25 2003

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Ruthenium
quinones
ruthenium
electron transfer
phenothiazines
Electrons
synthesis
electrons
Ground state
Rate constants
ground state
polarization (charge separation)
time constant
excitation
indication
life (durability)
benzoquinone
shift
decay

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone : Synthesis, characterization, and photoinduced electron transfer reactions. / Borgström, Magnus; Johansson, Olof; Lomoth, Reiner; Baudin, Helena Berglund; Wallin, Staffan; Sun, Licheng; Åkermark, Björn; Hammarström, Leif.

In: Inorganic Chemistry, Vol. 42, No. 17, 25.08.2003, p. 5173-5184.

Research output: Contribution to journalArticle

Borgström, Magnus ; Johansson, Olof ; Lomoth, Reiner ; Baudin, Helena Berglund ; Wallin, Staffan ; Sun, Licheng ; Åkermark, Björn ; Hammarström, Leif. / Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone : Synthesis, characterization, and photoinduced electron transfer reactions. In: Inorganic Chemistry. 2003 ; Vol. 42, No. 17. pp. 5173-5184.
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abstract = "Two electron donor-acceptor triads based on a benzoquinone acceptor linked to a light absorbing [Ru(bpy)3]2+ complex have been synthesized. In triad 6 (denoted RuII- BQ-CoIII), a [Co(bpy)3]3+ complex, a potential secondary acceptor, was linked to the quinone. In the other triad, 8 (denoted PTZ-RuII-BQ), a phenothiazine donor was linked to the ruthenium moiety. The corresponding dyads RuII-BQ (4) and PTZ-RuII (9) were prepared for comparison. Upon light excitation in the visible band of the ruthenium moiety, electron transfer to the quinone occurred with a rate constant kf = 5 × 109 s-1 (τf = 200 ps) in all the quinone containing complexes. Recombination to the ground state followed, with a rate constant kb ∼ 4.5 × 108 s-1 (τb ∼ 2.2 ns), for both RuII-BQ and Ru II-BQ-CoIII with no indication of a charge shift to generate the reduced CoII moiety. In the PTZ-RuII-BQ triad, however, the initial charge separation was followed by a rapid (k > 5 × 109 s-1) electron transfer from the phenothiazine moiety to give the fairly long-lived PTZ.+-RuII-BQ .- state (τ = 80 ns) in unusually high yield for a [Ru(bpy) 3]2+-based triad (> 90{\%}), that lies at ΔG° = 1.32 eV relative to the ground state. Unfortunately, this triad turned out to be rather photolabile. Interestingly, coupling between the oxidized PTZ .+ and the BQ.- moieties seemed to occur. This discouraged further extension to incorporate more redox active units. Finally, in the dyad PTZ-RuII a reversible, near isoergonic electron transfer was observed on excitation. Thus, a quasiequilibrium was established with an observed time constant of 7 ns, with ca. 82{\%} of the population in the PTZ-*RuII state and 18{\%} in the PTZ.+-Ru II(bpy.-) state. These states decayed in parallel with an observed lifetime of 90 ns. The initial electron transfer to form the PTZ .+-RuII(bpy.-) state was thus faster than what would have been inferred from the *RuII emission decay (τ = 90 ns). This result suggests that reports for related PTZ-RuII and PTZ-RuII-acceptor complexes in the literature might need to be reconsidered.",
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T1 - Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone

T2 - Synthesis, characterization, and photoinduced electron transfer reactions

AU - Borgström, Magnus

AU - Johansson, Olof

AU - Lomoth, Reiner

AU - Baudin, Helena Berglund

AU - Wallin, Staffan

AU - Sun, Licheng

AU - Åkermark, Björn

AU - Hammarström, Leif

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N2 - Two electron donor-acceptor triads based on a benzoquinone acceptor linked to a light absorbing [Ru(bpy)3]2+ complex have been synthesized. In triad 6 (denoted RuII- BQ-CoIII), a [Co(bpy)3]3+ complex, a potential secondary acceptor, was linked to the quinone. In the other triad, 8 (denoted PTZ-RuII-BQ), a phenothiazine donor was linked to the ruthenium moiety. The corresponding dyads RuII-BQ (4) and PTZ-RuII (9) were prepared for comparison. Upon light excitation in the visible band of the ruthenium moiety, electron transfer to the quinone occurred with a rate constant kf = 5 × 109 s-1 (τf = 200 ps) in all the quinone containing complexes. Recombination to the ground state followed, with a rate constant kb ∼ 4.5 × 108 s-1 (τb ∼ 2.2 ns), for both RuII-BQ and Ru II-BQ-CoIII with no indication of a charge shift to generate the reduced CoII moiety. In the PTZ-RuII-BQ triad, however, the initial charge separation was followed by a rapid (k > 5 × 109 s-1) electron transfer from the phenothiazine moiety to give the fairly long-lived PTZ.+-RuII-BQ .- state (τ = 80 ns) in unusually high yield for a [Ru(bpy) 3]2+-based triad (> 90%), that lies at ΔG° = 1.32 eV relative to the ground state. Unfortunately, this triad turned out to be rather photolabile. Interestingly, coupling between the oxidized PTZ .+ and the BQ.- moieties seemed to occur. This discouraged further extension to incorporate more redox active units. Finally, in the dyad PTZ-RuII a reversible, near isoergonic electron transfer was observed on excitation. Thus, a quasiequilibrium was established with an observed time constant of 7 ns, with ca. 82% of the population in the PTZ-*RuII state and 18% in the PTZ.+-Ru II(bpy.-) state. These states decayed in parallel with an observed lifetime of 90 ns. The initial electron transfer to form the PTZ .+-RuII(bpy.-) state was thus faster than what would have been inferred from the *RuII emission decay (τ = 90 ns). This result suggests that reports for related PTZ-RuII and PTZ-RuII-acceptor complexes in the literature might need to be reconsidered.

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