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Title: Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex

Abstract

We report the complex [Ru(deeb)(bpz) 2] 2+ ( RuBPZ 2+, deeb = 4,4'-diethylester-2,2'-bipyridine, bpz = 2,2'-bipyrazine) forms a single ion pair with bromide, [ RuBPZ 2+, Br ] +, with K eq = 8400 ± 200 M –1 in acetone. The RuBPZ 2+ displayed photoluminescence (PL) at room temperature with a lifetime of 1.75 μs. The addition of bromide to a RuBPZ 2+ acetone solution led to significant PL quenching and Stern–Volmer plots showed upward curvature. Time-resolved PL measurements identified two excited state quenching pathways, static and dynamic, which were operative toward [ RuBPZ 2+, Br ] + and free RuBPZ 2+, respectively. The single ion-pair [ RuBPZ 2+, Br ] +* had a lifetime of 45 ± 5 ns, consistent with an electron transfer rate constant, k et = (2.2 ± 0.3) × 10 7 s –1. In contrast, RuBPZ 2+* was dynamically quenched by bromide with a quenching rate constant, k q = (8.1 ± 0.1) × 10 10 M –1 s –1. Nanosecond transient absorption revealed that both the static and dynamic pathways yielded RuBPZ + and Br 2 •– products that underwent recombination to regenerate the ground state with a second-order rate constant, k cr =more » (2.3 ± 0.5) × 10 10 M –1 s –1. Kinetic analysis revealed that RuBPZ + was a primary photoproduct, while Br 2 •– was secondary product formed by the reaction of a Br with Br , k = (1.1 ± 0.2) × 10 10 M –1 s –1. Marcus theory afforded an estimate of the formal reduction potential for E 0(Br •/–) in acetone, 1.42 V vs NHE. A 1H NMR analysis indicated that the ion-paired bromide was preferentially situated close to the Ru II center. Prolonged steady state photolysis of RuBPZ 2+ and bromide yielded two ligand-substituted photoproducts, cis- and trans-Ru(deeb)(bpz)Br 2. Finally, a photochemical intermediate, proposed to be [Ru(deeb)(bpz)(κ 1-bpz)(Br)] +, was found to absorb a second photon to yield cis- and trans-Ru(deeb)(bpz)Br 2 photoproducts.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1]
  1. Univ. of North Carolina, Chapel Hill, NC (United States)
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Solar Fuels (UNC EFRC)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1470297
Grant/Contract Number:  
SC0001011
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 140; Journal Issue: 16; Related Information: UNC partners with University of North Carolina (lead); Duke University; University of Florida; Georgia Institute of Technology; University; North Carolina Central University; Research Triangle Institute; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (homogeneous); catalysis (heterogeneous); solar (photovoltaic); solar (fuels); photosynthesis (natural and artificial); hydrogen and fuel cells; electrodes - solar; charge transport; materials and chemistry by design; synthesis (novel materials); synthesis (self-assembly)

Citation Formats

Li, Guocan, Brady, Matthew D., and Meyer, Gerald J. Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex. United States: N. p., 2018. Web. doi:10.1021/jacs.8b00944.
Li, Guocan, Brady, Matthew D., & Meyer, Gerald J. Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex. United States. doi:10.1021/jacs.8b00944.
Li, Guocan, Brady, Matthew D., and Meyer, Gerald J. Thu . "Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex". United States. doi:10.1021/jacs.8b00944. https://www.osti.gov/servlets/purl/1470297.
@article{osti_1470297,
title = {Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex},
author = {Li, Guocan and Brady, Matthew D. and Meyer, Gerald J.},
abstractNote = {We report the complex [Ru(deeb)(bpz)2]2+ (RuBPZ2+, deeb = 4,4'-diethylester-2,2'-bipyridine, bpz = 2,2'-bipyrazine) forms a single ion pair with bromide, [RuBPZ2+, Br–]+, with Keq = 8400 ± 200 M–1 in acetone. The RuBPZ2+ displayed photoluminescence (PL) at room temperature with a lifetime of 1.75 μs. The addition of bromide to a RuBPZ2+ acetone solution led to significant PL quenching and Stern–Volmer plots showed upward curvature. Time-resolved PL measurements identified two excited state quenching pathways, static and dynamic, which were operative toward [RuBPZ2+, Br–]+ and free RuBPZ2+, respectively. The single ion-pair [RuBPZ2+, Br–]+* had a lifetime of 45 ± 5 ns, consistent with an electron transfer rate constant, ket = (2.2 ± 0.3) × 107 s–1. In contrast, RuBPZ2+* was dynamically quenched by bromide with a quenching rate constant, kq = (8.1 ± 0.1) × 1010 M–1 s–1. Nanosecond transient absorption revealed that both the static and dynamic pathways yielded RuBPZ+ and Br2•– products that underwent recombination to regenerate the ground state with a second-order rate constant, kcr = (2.3 ± 0.5) × 1010 M–1 s–1. Kinetic analysis revealed that RuBPZ+ was a primary photoproduct, while Br2•– was secondary product formed by the reaction of a Br• with Br–, k = (1.1 ± 0.2) × 1010 M–1 s–1. Marcus theory afforded an estimate of the formal reduction potential for E0(Br•/–) in acetone, 1.42 V vs NHE. A 1H NMR analysis indicated that the ion-paired bromide was preferentially situated close to the RuII center. Prolonged steady state photolysis of RuBPZ2+ and bromide yielded two ligand-substituted photoproducts, cis- and trans-Ru(deeb)(bpz)Br2. Finally, a photochemical intermediate, proposed to be [Ru(deeb)(bpz)(κ1-bpz)(Br)]+, was found to absorb a second photon to yield cis- and trans-Ru(deeb)(bpz)Br2 photoproducts.},
doi = {10.1021/jacs.8b00944},
journal = {Journal of the American Chemical Society},
number = 16,
volume = 140,
place = {United States},
year = {2018},
month = {3}
}

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