Use of inclusion complexes of hydrophibic viologens with cyclodextrin to protect the pyridinium moiety from hydrogenation in photochemical hydrogen formation

Okuno, Yohmei; Chiba, Yukihiro; Yonemitsu, Osamu

doi:10.1039/c39840001638

Cited by 14 publications

(12 citation statements)

References 2 publications

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“…The observation that the solution of the system not only turns blue but also cloudy suggests another explanation. Apparently, because of the reduced repulsion forces between the less positively charged monocation radicals when compared to those between the dication analogues, the reduced form of the viologen mediator associates in solution to form dimers, thereby interrupting partially, if not completely, the directional flow of electrons towards the catalytic center 19. This may account for the very low amount of hydrogen produced (Figure 1).…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, their reduction of water [Equation (1)] is efficiently catalyzed by a Pt surface. Cyclodextrins were selected as the host molecules for the self‐assembled system, as they are known to (i) counteract dimerization of the intermediates of the catalytic cycle (such as the reactive viologen radical cation [Me‐viol‐Me] · +[17–19] ), (ii) prevent the chemical reduction of [Me‐viol‐Me] + by the evolving hydrogen,19 and (iii) act as “molding matrices”20 or “supports”21 for the platinum colloids by solubilizing them in water without aggregation22,23 while keeping their surface accessible24 for hydrogen production. …”

Section: Introductionmentioning

confidence: 99%

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Variation of the Viologen Electron Relay in Cyclodextrin‐Based Self‐Assembled Systems for Photoinduced Hydrogen Evolution from Water

et al. 2012

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The light‐driven reduction of protons for the production of molecular hydrogen in multicomponent systems depends on electron relays such as viologens. We describe here the effect of viologens appended with guest moieties (adamantane or bile acid) on the efficiency of a system composed of a cyclodextrin‐appended photosensitizer [Ir(ppy)2(pytl‐βCD)]Cl [ppy = 2‐phenylpyridine; pytl = 2‐(1‐substituted‐1H‐1,2,3‐triazol‐4‐yl)pyridine; CD = cyclodextrin], cyclodextrin‐modified Pt nanoparticles as the catalyst, and ethylenediaminetetraacetic acid (EDTA) as the sacrificial donor. The system was designed to self‐assemble in a supramolecular manner in order to promote electron transfer and produce hydrogen. Cyclic voltammetry (CV) measurements in DMF showed that the electron‐donating adamantyl substituent decreases the reduction potential of the viologen. The use of symmetric and asymmetric guest‐appended viologens gave rise to unexpected phenomena in the H2 evolution. The presence of adamantane or bile acid groups on the viologen induced stabilization and aggregation of the radical cations in water, which is disadvantageous for hydrogen formation.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Variation of the Viologen Electron Relay in Cyclodextrin‐Based Self‐Assembled Systems for Photoinduced Hydrogen Evolution from Water

et al. 2012

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“…the highly reactive viologen radical cation [Me-V-Me] +38-40 ) and against the chemical reduction of [Me-V-Me] + by the evolving hydrogen. 40,41 Cyclodextrins have also been used as ''molding matrices'' 42 or ''supports'' 43,44 for the Pt colloids, showing a great influence on overall H 2 production probably due to the stabilization of the platinum colloid in solution.…”

Section: Introductionmentioning

confidence: 99%

Cyclodextrin-based systems for photoinduced hydrogen evolution

Mourtzis

Carballada

Felici

et al. 2011

Phys. Chem. Chem. Phys.

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Light-driven catalytic three component systems for the reduction of protons, consisting of a cyclodextrin-appended iridium complex as photosensitizer, a viologen-based electron relay, and cyclodextrin-modified platinum nanoparticles as the catalyst, were found to be capable of producing molecular hydrogen effectively in water, using a sacrificial electron donor. The modular approach introduced in this study allows the generation of several functional photo-active systems by self-assembly from a limited number of building blocks. We established that systems with polypyridine iridium complexes of general formula [Ir(ppy)(2)(pytl-R)]Cl (ppy, 2-phenylpyridine; pytl, 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine) as photosensitizers are active in the production of H(2), with yields that under our experimental conditions are 20-35 times higher than those of the classical system with [Ru(bpy)(3)]Cl(2) (bpy, 2,2'-bipyridine), methyl viologen, and Pt. By investigating different photocatalytic systems, it was found that the amount of hydrogen produced was directly proportional to the emission quantum yield of the photosensitizer.

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“…This has been established by several groups over the years using techniques as varied as cyclic voltammetry and 1 H-NMR. [39][40][41] Therefore, in our system, methyl viologen acts as an exclusively water-based quencher in much the same way the smaller ionic quenchers do.…”

Section: Quenching Study and The Influence Of Ionic Strengthmentioning

confidence: 77%

A ground-state complex between methyl viologen and the fluorescent whitening agent 4,4′-bis(2-sulfostyryl)-biphenyl disodium salt: a fluorescence spectroscopy study

et al. 2021

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This study explores the quenching of the dianionic fluorescent whitening agent, NFW, by various substances, including methyl viologen (MV), in water and in the presence of Beta-cyclodextrin (β-CD). Results of a fluorescence spectroscopic examination of the β-CD-NFW system are presented. It was found that NFW forms a 1:1 inclusion complex with β-CD with an association constant of 2540 ± 380 M-1. The included NFW fluorescent state is protected by the β-CD cavity from a range of water-based quenchers (neutral, anionic and cationic). Quenching proceeds near the diffusion-controlled limit in water for the quenchers tested with the exception of the dicationic MV. MV is an extremely efficient quencher of NFW fluorescence with a nominal KSV ~ 5.0x103 M-1 in water alone, corresponding to a nominal kq of ~ 4x1012 M-1s-1, which exceeds the diffusion-controlled limit in this solvent. The quenching efficiency of MV is strongly suppressed in the presence of 10 mM β-CD (KSV = 105 ± 12 M-1) and in the presence of NaCl (KSV = 106 ± 9 M-1 at 0.5 M salt). In the absence of CD or salt, there is a strong contribution from static quenching in the MV system; the presence of these additives suppresses the static quenching. Various results suggest the static quenching is due to formation of a ground-state complex between the dianion NFW and the dication MV.

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Use of inclusion complexes of hydrophibic viologens with cyclodextrin to protect the pyridinium moiety from hydrogenation in photochemical hydrogen formation

Abstract: Cyclodextrin inclusion complexes of viologens with hydrophobic tails increased the stability of the pyridinium moiety of the viologen to hydrogenation, which resulted in up to five times higher efficiency in terms of hydrogen produced per viologen consumed.

Cited by 14 publications

References 2 publications

Variation of the Viologen Electron Relay in Cyclodextrin‐Based Self‐Assembled Systems for Photoinduced Hydrogen Evolution from Water

Variation of the Viologen Electron Relay in Cyclodextrin‐Based Self‐Assembled Systems for Photoinduced Hydrogen Evolution from Water

Cyclodextrin-based systems for photoinduced hydrogen evolution

A ground-state complex between methyl viologen and the fluorescent whitening agent 4,4′-bis(2-sulfostyryl)-biphenyl disodium salt: a fluorescence spectroscopy study

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