Verification of the electron/proton coupled mechanism for phenolic H-atom transfer using a triplet π,π∗ carbonyl

Yamaji, Minoru; Oshima, Juro; Hidaka, M.

doi:10.1016/j.cplett.2009.05.063

Cited by 13 publications

(15 citation statements)

References 41 publications

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“… [a] From ref. 15, converted from volts versus saturated calomel electrode (SCE) to volts versus Fc + /Fc by subtracting 0.38 V as described in ref. 16.…”

Section: Resultsmentioning

confidence: 99%

Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex

et al. 2013

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Two pyridylphenols with intramolecular hydrogen bonds between the phenol and pyridine units were synthesized, characterized crystallographically, and investigated by cyclic voltammetry and UVvis spectroscopy. Reductive quenching of the 3 MLCT excited state of the [Re(phen)(CO)3(py)]+ complex (phen = 1,10-phenanthroline, py = pyridine) by the two pyridylphenols and two reference phenol molecules was investigated by steady-state and time-resolved luminescence spectroscopy, as well as by transient absorption spectroscopy. Stern-Volmer analysis of the luminescence quenching data provides rate constants for the bimolecular excited-state quenching reactions. H/D kinetic isotope effects (KIEs) for the pyridylphenols are on the order of 2.0, and the bimolecular quenching reactions are up to 100 times faster with the pyridylphenols than with the reference phenols. This observation is attributed to the markedly less positive oxidation potentials of the pyridylphenols with respect to the reference phenols (ca. 0.5 V), which in turn is caused by protoncoupling of the phenol oxidation process. Transient absorption spectroscopy provides unambiguous evidence for the photogeneration of phenoxyl radicals, i. e., the overall photoreaction is clearly a PCET process

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“… [a] From ref. 15, converted from volts versus saturated calomel electrode (SCE) to volts versus Fc + /Fc by subtracting 0.38 V as described in ref. 16.…”

Section: Resultsmentioning

confidence: 99%

Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex

et al. 2013

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“…triplet population upon light irradiation, since the lowlying lone pair electrons on the oxygen p orbital facilitate the hybridization of n-π* and π-π* transitions, although no heavy atoms exist. Nevertheless, despite that a diphenyl ketone usually holds a high energy T 1 state to grab one hydrogen atom directly from other compounds (e.g., alkyl substituted compounds) upon UV irradiation [35,47,48], the triplet energy of ketocoumarin (e.g., KCD) is not high enough to grab one hydrogen atom directly from other compounds [46]. Therefore, only the coinitiator with a low oxidation potential (e.g., NPG) can react with the excited KCD via proton coupled electron transfer (PCET) [13,46].…”

Section: Figurementioning

confidence: 99%

“…Nevertheless, despite that a diphenyl ketone usually holds a high energy T 1 state to grab one hydrogen atom directly from other compounds (e.g., alkyl substituted compounds) upon UV irradiation [35,47,48], the triplet energy of ketocoumarin (e.g., KCD) is not high enough to grab one hydrogen atom directly from other compounds [46]. Therefore, only the coinitiator with a low oxidation potential (e.g., NPG) can react with the excited KCD via proton coupled electron transfer (PCET) [13,46]. When irradiating the KCD/NPG "photoinitibitor" in toluene by a 400 nm pulse laser, NPG is not excited and also does not influence the formation of KCD S 1 state and the ISC process from the S 1 to T 1 state (Fig.…”

Section: Figurementioning

confidence: 99%

Effect of ketyl radical on the structure and performance of holographic polymer/liquid-crystal composites

et al. 2019

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Holographic polymer/liquid-crystal composites, which are periodically ordered materials with alternative polymer-rich and liquid-crystal-rich phases, have drawn increasing interest due to their unique capabilities of reconstructing colored three-dimensional (3D) images and enabling the electro-optic response. They are formed via photopolymerization induced phase separation upon exposure to laser interference patterns, where a fast photopolymerization is required to facilitate the holographic patterning. Yet, the fast photopolymerization generally leads to depressed phase separation and it remains challenging to boost the holographic performance via kinetics control. Herein, we disclose that the ketyl radical inhibition is able to significantly boost the phase separation and holographic performance by preventing the proliferated diffusion of initiating radicals from the constructive to the destructive regions. Dramatically depressed phase separation is caused when converting the inhibiting ketyl radical to a new initiating radical, indicating the significance of ketyl radical inhibition when designing high performance holographic polymer composites.Scheme 1 Schematic illustration on the conversion of the ketyl radical with an inhibition function to a new initiating radical and the corresponding ordered structures.Scheme 5 Proposed radical diffusion during holographic photopolymerization.

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“…2+ is highly inefficient. 47 In CH 3 CN-H 2 O mixtures the 3 MLCT luminescence of the dyads is quenched, and the excited-state lifetimes shorten to 148 ns for CN-PhOH-Ru 2+ and B20 ns for PhOH-Ru 2+ while that of the reference complex is 772 ns (Fig. S3, ESI †).…”

Section: +mentioning

confidence: 99%

Long-range proton-coupled electron transfer in phenol–Ru(2,2′-bipyrazine)32+ dyads

Bronner

Wenger

2014

Phys. Chem. Chem. Phys.

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Two dyads in which either 4-cyanophenol or un-substituted phenol is connected via a p-xylene spacer to a Ru(bpz)3(2+) (bpz = 2,2'-bipyrazine) complex were synthesized and investigated. Selective photo-excitation of Ru(bpz)3(2+) at 532 nm in a CH3CN-H2O mixture leads to the formation of 4-cyanophenolate or phenolate along with Ru(bpz)3(2+) in its electronic ground state. This apparent photoacid behavior can be understood on the basis of a reaction sequence comprised of an initial photoinduced proton-coupled electron transfer (PCET) during which 4-cyanophenol or phenol is oxidized and deprotonated, followed by a thermal electron transfer event in the course of which 4-cyanophenoxyl or phenoxyl is reduced by Ru(bpz)3(+) to 4-cyanophenolate or phenolate. Conceptually, this reaction sequence is identical to a sequence of photoinduced charge-separation and thermal charge-recombination events as observed previously for many electron transfer dyads, with the important difference that the initial photoinduced electron transfer process is proton-coupled. The dyad containing 4-cyanophenol reacts via concerted-proton electron transfer (CPET) whereas the dyad containing un-substituted phenol appears to react predominantly via a stepwise PCET mechanism. Long-range PCET is a key reaction in photosystem II. Understanding the factors that govern the kinetics of long-range PCET is desirable in the broader context of light-to-energy conversion by means of proton-electron separation across natural or artificial membranes.

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Verification of the electron/proton coupled mechanism for phenolic H-atom transfer using a triplet π,π∗ carbonyl

Cited by 13 publications

References 41 publications

Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex

Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex

Effect of ketyl radical on the structure and performance of holographic polymer/liquid-crystal composites

Long-range proton-coupled electron transfer in phenol–Ru(2,2′-bipyrazine)32+ dyads

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