Titanyl Phthalocyanine as a Water Photooxidation Agent

Morawski, Olaf; Izdebska, Katarzyna; Karpiuk, Elena; Suchocki, A.; Zhydachevskyy, Yaroslav; Sobolewski, Andrzej L.

doi:10.1021/acs.jpcc.5b05083

Cited by 7 publications

(7 citation statements)

References 43 publications

(108 reference statements)

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“…In the present heptazine–water complex, the excessive energy available through the radiationless relaxation from the higher bright state to S1 and the solvent rearrangement will suppress any barriers (ref ; linear interpolation via relative distances of the proton with donor oxygen and accepted nitrogen atoms in the heptazine–water system). The predicted photochemical picture of the heptazine–water complex for water splitting (with heptazine, the backbone of g-C 3 N 4 materials) reveals the possibility of biradical detection on an experimental scale, as does the earlier reported generation of OH radicals with titanium oxide materials. − …”

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confidence: 58%

Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C₃N₄

Ullah

Chen

Zhao

et al. 2019

J. Phys. Chem. Lett.

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Heptazine-assembled polymeric carbon nitride (CN) materials have fascinated the research community as a photocatalyst for hydrogen evolution while less attention has been devoted to the mechanistic features of the host materials. Using excited-state nonadiabatic dynamics simulations, the molecular-level picture of the decomposition of heptazine hydrogen bonded to water molecule(s) (heptazine−water complex) into heptazinyl and hydroxyl biradical products is revealed. Dynamics simulations show that hydrogen detachment from the water molecule to the heptazine occurs within tens of femtoseconds and suggest that excited-state deactivation via N− H••••••O−H electron-driven proton transfer (EDPT) is the dominant and most relevant excited-state deactivation process in heptazine−water complexes leading to conical intersection. The observation of photorelaxation-induced water splitting by heptazine is proof of the water-splitting reaction principle, which presents further challenges for computational and experimental investigations of the deactivation of heptazinyl and OH biradical products for efficient hydrogen evolution.

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confidence: 58%

Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C₃N₄

Ullah

Chen

Zhao

et al. 2019

J. Phys. Chem. Lett.

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“…Terephthalic acid is a well-known • OH scavenger that is nonluminescent until reacting with • OH to form 2hydroxyterephthalic acid, which exhibits characteristic luminescence at 430 nm. 43,44 We observe a linear increase in 2hydroxyterephthalate PL with illumination time, indicating TAHz in H 2 O photochemically liberates • OH.…”

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confidence: 76%

Proton-Coupled Electron Transfer from Water to a Model Heptazine-Based Molecular Photocatalyst

Rabe

Corp

Sobolewski

et al. 2018

J. Phys. Chem. Lett.

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To gain mechanistic understanding of heptazine-based photochemistry, we synthesized and studied 2,5,8-tris(4-methoxyphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (TAHz), a model molecular photocatalyst chemically related to carbon nitride. On the basis of time-resolved photoluminescence (TR-PL) spectroscopy, we kinetically reveal a new feature that emerges in aqueous dispersions of TAHz. Using global target analysis, we spectrally and kinetically resolve the new emission feature to be blue shifted from the steady-state luminescence, and observe a fast decay component exhibiting a kinetic isotope effect (KIE) of 2.9 in H2O versus D2O, not observed in the steady-state PL. From ab initio electronic-structure calculations, we attribute this new PL peak to the fluorescence of an upper excited state of mixed nπ*/ππ* character. In water, the KIE suggests the excited state is quenched by proton-coupled electron transfer, liberating hydroxyl radicals that we detect using terephthalic acid. Our findings are consistent with recent theoretical predictions that heptazine-based photocatalysts can participate in proton-coupled electron transfer with H2O.

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“…In scenario I, free OH radicals as well as free H radicals are generated. It should be possible to detect the OH radicals in situ by chemical scavenging and spectroscopic (laser-induced fluorescence) detection of the hydroxylated products, as demonstrated recently for OH radicals generated with TiO 2 materials (anatase, rutile) − or titanyl porphyrin/phthalocyanine molecular photocatalysts. , In scenario II, no free H radicals are generated. The in situ detection of H radicals could thus differentiate between the two scenarios.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of Photocatalytic Water Splitting with Graphitic Carbon Nitride: Photochemistry of the Heptazine–Water Complex

et al. 2017

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Impressive progress has recently been achieved in photocatalytic hydrogen evolution with polymeric carbon nitride materials consisting of heptazine building blocks. However, the fundamental mechanistic principles of the catalytic cycle are as yet poorly understood. Here, we provide first-principles computational evidence that water splitting with heptazine-based materials can be understood as a molecular excited-state reaction taking place in hydrogen-bonded heptazine-water complexes. The oxidation of water occurs homolytically via an electron/proton transfer from water to heptazine, resulting in ground-state heptazinyl and OH radicals. It is shown that the excess hydrogen atom of the heptazinyl radical can be photodetached by a second photon, which regenerates the heptazine molecule. Alternatively to the photodetachment reaction, two heptazinyl radicals can recombine in a dark reaction to form H, thereby regenerating two heptazine molecules. The proposed molecular photochemical reaction scheme within hydrogen-bonded chromophore-water complexes is complementary to the traditional paradigm of photocatalytic water splitting, which assumes the separation of electrons and holes over substantial time scales and distances.

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Titanyl Phthalocyanine as a Water Photooxidation Agent

Cited by 7 publications

References 43 publications

Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C₃N₄

Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C₃N₄

Proton-Coupled Electron Transfer from Water to a Model Heptazine-Based Molecular Photocatalyst

Mechanism of Photocatalytic Water Splitting with Graphitic Carbon Nitride: Photochemistry of the Heptazine–Water Complex

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Titanyl Phthalocyanine as a Water Photooxidation Agent

Cited by 7 publications

References 43 publications

Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C3N4

Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C3N4

Proton-Coupled Electron Transfer from Water to a Model Heptazine-Based Molecular Photocatalyst

Mechanism of Photocatalytic Water Splitting with Graphitic Carbon Nitride: Photochemistry of the Heptazine–Water Complex

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Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C₃N₄

Photoinduced Water–Heptazine Electron-Driven Proton Transfer: Perspective for Water Splitting with g-C₃N₄