Mechanistic studies of photoinduced intramolecular and intermolecular electron transfer processes in RuPt-centred photo-hydrogen-evolving molecular devices

Chettiyam Veettil Suneesh, Bijitha Balan, Hironobu Ozawa, Yuki Nakamura, Tetsuro Katayama, Masayasu Muramatsu, Yutaka Nagasawa, Hiroshi Miyasaka, Ken Sakai

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Abstract

The photoinduced electron transfer properties of two photo-hydrogen- evolving molecular devices (PHEMDs) [(bpy)2Ru(ii)(phen-NHCO-bpy-R) Pt(ii)Cl2]2+ (i.e., condensation products of [Ru(bpy) 2(5-amino-phen)]2+ and (4-carboxy-4′-R-bpy)PtCl 2; bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline; RuPt-COOH for R = COOH and RuPt-CN for R = CN) were investigated. RuPt-CN demonstrates higher photocatalytic performance relative to RuPt-COOH arising from a larger driving force for the intramolecular photoinduced electron transfer (PET) associated with a stronger electron-withdrawing effect of R (ΔG PET = -0.43 eV for RuPt-CN and -0.16 eV for RuPt-COOH). This is the first study on PET events using ultrafast spectroscopy. Dramatic enhancement is achieved in the rate of PET in RuPt-CN (1.78 × 1010 s -1) relative to RuPt-COOH (3.1 × 109 s -1). For each system, the presence of three different conformers giving rise to three different PET rates is evidenced, which are also discussed with the DFT results. Formation of a charge-separated (CS) state [(bpy) 2Ru(iii)(phen-NHCO-bpy--R)Pt(ii)Cl2] 2+ in the sub-picosecond time regime and recombination in the picosecond time regime are characterized spectrophotometrically. The CS-state formation was found to compete with reductive quenching of the triplet excited state by EDTA whose dianionic form ion-pairs with dicationic RuPt-COOH. Thus, a key intermediate [(bpy)2Ru(ii)(phen-NHCO-bpy--R)Pt(ii) Cl2]+ (i.e., the one-electron-reduced species) prior to the H2 formation was found to be formed either via reduction of the CS state by EDTA or via formation of [(bpy)2Ru(ii)(phen --NHCO-bpy-R)Pt(ii)Cl2]+ by reductive quenching of the triplet excited state. More importantly, it is also shown that some of the conformers in solution possess a CS lifetime sufficiently long to drive hydrogen evolution from water.

Original languageEnglish
Pages (from-to)1607-1616
Number of pages10
JournalPhysical Chemistry Chemical Physics
Volume16
Issue number4
DOIs
Publication statusPublished - Jan 28 2014

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Hydrogen
electron transfer
Electrons
hydrogen
ethylenediaminetetraacetic acids
quenching
Excited states
Edetic Acid
Quenching
excitation
electrons
condensation
Discrete Fourier transforms
Condensation
life (durability)
augmentation
Spectroscopy
Ions
products
water

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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Mechanistic studies of photoinduced intramolecular and intermolecular electron transfer processes in RuPt-centred photo-hydrogen-evolving molecular devices. / Suneesh, Chettiyam Veettil; Balan, Bijitha; Ozawa, Hironobu; Nakamura, Yuki; Katayama, Tetsuro; Muramatsu, Masayasu; Nagasawa, Yutaka; Miyasaka, Hiroshi; Sakai, Ken.

In: Physical Chemistry Chemical Physics, Vol. 16, No. 4, 28.01.2014, p. 1607-1616.

Research output: Contribution to journalArticle

Suneesh, Chettiyam Veettil ; Balan, Bijitha ; Ozawa, Hironobu ; Nakamura, Yuki ; Katayama, Tetsuro ; Muramatsu, Masayasu ; Nagasawa, Yutaka ; Miyasaka, Hiroshi ; Sakai, Ken. / Mechanistic studies of photoinduced intramolecular and intermolecular electron transfer processes in RuPt-centred photo-hydrogen-evolving molecular devices. In: Physical Chemistry Chemical Physics. 2014 ; Vol. 16, No. 4. pp. 1607-1616.
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AU - Balan, Bijitha

AU - Ozawa, Hironobu

AU - Nakamura, Yuki

AU - Katayama, Tetsuro

AU - Muramatsu, Masayasu

AU - Nagasawa, Yutaka

AU - Miyasaka, Hiroshi

AU - Sakai, Ken

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N2 - The photoinduced electron transfer properties of two photo-hydrogen- evolving molecular devices (PHEMDs) [(bpy)2Ru(ii)(phen-NHCO-bpy-R) Pt(ii)Cl2]2+ (i.e., condensation products of [Ru(bpy) 2(5-amino-phen)]2+ and (4-carboxy-4′-R-bpy)PtCl 2; bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline; RuPt-COOH for R = COOH and RuPt-CN for R = CN) were investigated. RuPt-CN demonstrates higher photocatalytic performance relative to RuPt-COOH arising from a larger driving force for the intramolecular photoinduced electron transfer (PET) associated with a stronger electron-withdrawing effect of R (ΔG PET = -0.43 eV for RuPt-CN and -0.16 eV for RuPt-COOH). This is the first study on PET events using ultrafast spectroscopy. Dramatic enhancement is achieved in the rate of PET in RuPt-CN (1.78 × 1010 s -1) relative to RuPt-COOH (3.1 × 109 s -1). For each system, the presence of three different conformers giving rise to three different PET rates is evidenced, which are also discussed with the DFT results. Formation of a charge-separated (CS) state [(bpy) 2Ru(iii)(phen-NHCO-bpy--R)Pt(ii)Cl2] 2+ in the sub-picosecond time regime and recombination in the picosecond time regime are characterized spectrophotometrically. The CS-state formation was found to compete with reductive quenching of the triplet excited state by EDTA whose dianionic form ion-pairs with dicationic RuPt-COOH. Thus, a key intermediate [(bpy)2Ru(ii)(phen-NHCO-bpy--R)Pt(ii) Cl2]+ (i.e., the one-electron-reduced species) prior to the H2 formation was found to be formed either via reduction of the CS state by EDTA or via formation of [(bpy)2Ru(ii)(phen --NHCO-bpy-R)Pt(ii)Cl2]+ by reductive quenching of the triplet excited state. More importantly, it is also shown that some of the conformers in solution possess a CS lifetime sufficiently long to drive hydrogen evolution from water.

AB - The photoinduced electron transfer properties of two photo-hydrogen- evolving molecular devices (PHEMDs) [(bpy)2Ru(ii)(phen-NHCO-bpy-R) Pt(ii)Cl2]2+ (i.e., condensation products of [Ru(bpy) 2(5-amino-phen)]2+ and (4-carboxy-4′-R-bpy)PtCl 2; bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline; RuPt-COOH for R = COOH and RuPt-CN for R = CN) were investigated. RuPt-CN demonstrates higher photocatalytic performance relative to RuPt-COOH arising from a larger driving force for the intramolecular photoinduced electron transfer (PET) associated with a stronger electron-withdrawing effect of R (ΔG PET = -0.43 eV for RuPt-CN and -0.16 eV for RuPt-COOH). This is the first study on PET events using ultrafast spectroscopy. Dramatic enhancement is achieved in the rate of PET in RuPt-CN (1.78 × 1010 s -1) relative to RuPt-COOH (3.1 × 109 s -1). For each system, the presence of three different conformers giving rise to three different PET rates is evidenced, which are also discussed with the DFT results. Formation of a charge-separated (CS) state [(bpy) 2Ru(iii)(phen-NHCO-bpy--R)Pt(ii)Cl2] 2+ in the sub-picosecond time regime and recombination in the picosecond time regime are characterized spectrophotometrically. The CS-state formation was found to compete with reductive quenching of the triplet excited state by EDTA whose dianionic form ion-pairs with dicationic RuPt-COOH. Thus, a key intermediate [(bpy)2Ru(ii)(phen-NHCO-bpy--R)Pt(ii) Cl2]+ (i.e., the one-electron-reduced species) prior to the H2 formation was found to be formed either via reduction of the CS state by EDTA or via formation of [(bpy)2Ru(ii)(phen --NHCO-bpy-R)Pt(ii)Cl2]+ by reductive quenching of the triplet excited state. More importantly, it is also shown that some of the conformers in solution possess a CS lifetime sufficiently long to drive hydrogen evolution from water.

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