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Title: Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO 2 reduction using time-resolved IR measurements

Abstract

Supramolecular photocatalysts in which Ru(II) photosensitizer and Re(I) catalyst units are connected to each other by an ethylene linker are among the best known, most effective and durable photocatalytic systems for CO 2 reduction. In this paper we report, for the first time, time-resolved infrared (TRIR) spectra of three of these binuclear complexes to uncover why the catalysts function so efficiently. Selective excitation of the Ru unit with a 532 nm laser pulse induces slow intramolecular electron transfer from the 3MLCT excited state of the Ru unit to the Re unit, with rate constants of (1.0–1.1) × 10 4 s -1 as a major component and (3.5–4.3) × 10 6 s -1 as a minor component, in acetonitrile. The produced charge-separated state has a long lifetime, with charge recombination rate constants of only (6.5–8.4) × 10 4 s -1. Thus, although it has a large driving force (-ΔG 0 CR ~ 2.6 eV), this process is in the Marcus inverted region. On the other hand, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH), reductive quenching of the excited Ru unit proceeds much faster (k q[BNAH (0.2 M)] = (3.5–3.8) × 10 6 s -1) than the abovementioned intramolecular oxidative quenching, producing themore » one-electron-reduced species (OERS) of the Ru unit. Nanosecond TRIR data clearly show that intramolecular electron transfer from the OERS of the Ru unit to the Re unit (k ET > 2 × 10 7 s -1) is much faster than from the excited state of the Ru unit, and that it is also faster than the reductive quenching process of the excited Ru unit by BNAH. To measure the exact value of k ET, picosecond TRIR spectroscopy and a stronger reductant were used. Thus, in the case of the binuclear complex with tri(p-fluorophenyl)phosphine ligands (RuRe(FPh)), for which intramolecular electron transfer is expected to be the fastest among the three binuclear complexes, in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), k ET was measured as k ET = (1.4 ± 0.1) × 10 9 s -1. This clearly shows that intramolecular electron transfer in these RuRe binuclear supramolecular photocatalysts is not the rate-determining process in the photocatalytic reduction of CO 2, which is one of the main reasons why they work so efficiently.« less

Authors:
 [1]; ORCiD logo [2];  [3]; ORCiD logo [2];  [3];  [3];  [4];  [3];  [4]; ORCiD logo [3]
  1. National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Division
  3. Tokyo Inst. of Technology (Japan). Dept. of Chemistry
  4. Kyushu Univ., Fukuoka (Japan). Dept. of Chemistry
Publication Date:
Research Org.:
National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan); Kyushu Univ., Fukuoka (Japan); Tokyo Inst. of Technology (Japan); Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Ministry of Economy, Trade and Industry (METI) (Japan); Japan Science and Technology Agency (JST); Japan Society for the Promotion of Science (JSPS)
OSTI Identifier:
1422239
Alternate Identifier(s):
OSTI ID: 1425101
Report Number(s):
BNL-203320-2018-JAAM
Journal ID: ISSN 2041-6520
Grant/Contract Number:  
SC0012704; JPMJCR13L1; JP17H06375
Resource Type:
Journal Article: Published Article
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 9; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 47 OTHER INSTRUMENTATION

Citation Formats

Koike, Kazuhide, Grills, David C., Tamaki, Yusuke, Fujita, Etsuko, Okubo, Kei, Yamazaki, Yasuomi, Saigo, Masaki, Mukuta, Tatsuhiko, Onda, Ken, and Ishitani, Osamu. Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO2 reduction using time-resolved IR measurements. United States: N. p., 2018. Web. doi:10.1039/C7SC05338J.
Koike, Kazuhide, Grills, David C., Tamaki, Yusuke, Fujita, Etsuko, Okubo, Kei, Yamazaki, Yasuomi, Saigo, Masaki, Mukuta, Tatsuhiko, Onda, Ken, & Ishitani, Osamu. Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO2 reduction using time-resolved IR measurements. United States. doi:10.1039/C7SC05338J.
Koike, Kazuhide, Grills, David C., Tamaki, Yusuke, Fujita, Etsuko, Okubo, Kei, Yamazaki, Yasuomi, Saigo, Masaki, Mukuta, Tatsuhiko, Onda, Ken, and Ishitani, Osamu. Wed . "Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO2 reduction using time-resolved IR measurements". United States. doi:10.1039/C7SC05338J.
@article{osti_1422239,
title = {Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO2 reduction using time-resolved IR measurements},
author = {Koike, Kazuhide and Grills, David C. and Tamaki, Yusuke and Fujita, Etsuko and Okubo, Kei and Yamazaki, Yasuomi and Saigo, Masaki and Mukuta, Tatsuhiko and Onda, Ken and Ishitani, Osamu},
abstractNote = {Supramolecular photocatalysts in which Ru(II) photosensitizer and Re(I) catalyst units are connected to each other by an ethylene linker are among the best known, most effective and durable photocatalytic systems for CO2 reduction. In this paper we report, for the first time, time-resolved infrared (TRIR) spectra of three of these binuclear complexes to uncover why the catalysts function so efficiently. Selective excitation of the Ru unit with a 532 nm laser pulse induces slow intramolecular electron transfer from the 3MLCT excited state of the Ru unit to the Re unit, with rate constants of (1.0–1.1) × 104 s-1 as a major component and (3.5–4.3) × 106 s-1 as a minor component, in acetonitrile. The produced charge-separated state has a long lifetime, with charge recombination rate constants of only (6.5–8.4) × 104 s-1. Thus, although it has a large driving force (-ΔG0CR ~ 2.6 eV), this process is in the Marcus inverted region. On the other hand, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH), reductive quenching of the excited Ru unit proceeds much faster (kq[BNAH (0.2 M)] = (3.5–3.8) × 106 s-1) than the abovementioned intramolecular oxidative quenching, producing the one-electron-reduced species (OERS) of the Ru unit. Nanosecond TRIR data clearly show that intramolecular electron transfer from the OERS of the Ru unit to the Re unit (kET > 2 × 107 s-1) is much faster than from the excited state of the Ru unit, and that it is also faster than the reductive quenching process of the excited Ru unit by BNAH. To measure the exact value of kET, picosecond TRIR spectroscopy and a stronger reductant were used. Thus, in the case of the binuclear complex with tri(p-fluorophenyl)phosphine ligands (RuRe(FPh)), for which intramolecular electron transfer is expected to be the fastest among the three binuclear complexes, in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), kET was measured as kET = (1.4 ± 0.1) × 109 s-1. This clearly shows that intramolecular electron transfer in these RuRe binuclear supramolecular photocatalysts is not the rate-determining process in the photocatalytic reduction of CO2, which is one of the main reasons why they work so efficiently.},
doi = {10.1039/C7SC05338J},
journal = {Chemical Science},
number = ,
volume = 9,
place = {United States},
year = {Wed Feb 14 00:00:00 EST 2018},
month = {Wed Feb 14 00:00:00 EST 2018}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1039/C7SC05338J

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