Electrochemical Studies of Zinc Tetraphenylporphin

Lanese, J. G.; Wilson, George S.

doi:10.1149/1.2404391

Cited by 86 publications

(73 citation statements)

References 3 publications

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“…-1.9 V is applied, a very broad peak centered at 769 nm is observed (blue curve). This peak is consistent with the spectral features reported for metallophlorins (32,33), including those of nickel phlorins (30).…”

Section: -H]supporting

confidence: 90%

Nickel phlorin intermediate formed by proton-coupled electron transfer in hydrogen evolution mechanism

Solis

Maher

Dogutan

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

152

147

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The development of more effective energy conversion processes is critical for global energy sustainability. The design of molecular electrocatalysts for the hydrogen evolution reaction is an important component of these efforts. Proton-coupled electron transfer (PCET) reactions, in which electron transfer is coupled to proton transfer, play an important role in these processes and can be enhanced by incorporating proton relays into the molecular electrocatalysts. Herein nickel porphyrin electrocatalysts with and without an internal proton relay are investigated to elucidate the hydrogen evolution mechanisms and thereby enable the design of more effective catalysts. Density functional theory calculations indicate that electrochemical reduction leads to dearomatization of the porphyrin conjugated system, thereby favoring protonation at the meso carbon of the porphyrin ring to produce a phlorin intermediate. A key step in the proposed mechanisms is a thermodynamically favorable PCET reaction composed of intramolecular electron transfer from the nickel to the porphyrin and proton transfer from a carboxylic acid hanging group or an external acid to the meso carbon of the porphyrin. The C-H bond of the active phlorin acts similarly to the more traditional metal-hydride by reacting with acid to produce H 2 . Support for the theoretically predicted mechanism is provided by the agreement between simulated and experimental cyclic voltammograms in weak and strong acid and by the detection of a phlorin intermediate through spectroelectrochemical measurements. These results suggest that phlorin species have the potential to perform unique chemistry that could prove useful in designing more effective electrocatalysts.electrocatalysis | metalloporphyrin | proton transfer | dearomatization D irect solar-to-fuel processes are important components of global energy sustainability efforts (1, 2). Such processes include the hydrogen evolution reaction (HER), oxidation of water to oxygen, and reduction of CO 2 to hydrocarbons (3, 4). Protoncoupled electron transfer (PCET), which is generally defined in terms of coupling between electron transfer (ET) and proton transfer (PT) reactions, is essential to all of these processes. PCET can be classified as occurring via either a sequential or a concerted mechanism (5, 6). The mechanism is determined to be sequential rather than concerted if a stable intermediate associated with initial ET or PT can be identified. This distinction is not rigorous, however, because the identification of a stable intermediate may depend on the experimental approach or the level of theory, as well as the lifetime of the intermediate. Regardless of the specific mechanism, the coupling of ET and PT plays a significant role in a wide range of energy conversion processes (7-11). Moreover, the coupling of ET and PT can be enhanced by incorporating proton relays into molecular catalysts, exploiting the proximal positioning of the proton donor and acceptor (12-16). Recognition and characterization of successful PCET ...

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Section: -H]supporting

confidence: 90%

Nickel phlorin intermediate formed by proton-coupled electron transfer in hydrogen evolution mechanism

Solis

Maher

Dogutan

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

152

147

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“…Closs and Closs overcame this problem by reducing ZnTPP(À2) chemically with sodium benzophenone ketyl to form [ZnTPP(À3)] À and [ZnTPP(À4)] 2À in tetrahydrofuran [68]. Wilson et al were able to form [ZnTPP(À3)] À in DMF using a thin layer spectroelectrochemical cell [69]. A hydrazine reduction method pioneered by Belarussian workers can be used to form stable solutions of anion radicals of porphyrin complexes [70][71][72].…”

Section: Spectral Band Assignments-metalloporphyrinsmentioning

confidence: 99%

Assignment of the optical spectrum of metal porphyrin and phthalocyanine radical anions

Mack

Stillman

2001

J. Porphyrins Phthalocyanines

118

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The approach developed previously to assign the major π → π* and π* → π* bands in the optical spectra of metallophthalocyanine radical species [ MPc (−n)](n−2)− (n = 1–6), which was based on spectral band deconvolution analyses of the UV-vis absorption and magnetic circular dichroism (MCD) spectra and ZINDO calculations, is reviewed in this paper and extended to the major bands observed in the spectrum of the zinc tetraphenylporphyrin radical anion [ ZnTPP (−3)]−. The magnetic circular dichroism spectrum is dominated by an intense pseudo A term associated with the B (or Soret) transition with bands at 445 and 465 nm. Weaker bands associated with the π* → π* transition out of the partially filled LUMO give rise to two widely separated, oppositely signed, coupled B terms in the MCD spectrum at 538 and 910 nm. The Q transition is assigned to a weak absorption band at 750 nm and a shoulder slightly to the blue at 728 nm.

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“…The electrochemical behaviour of the porphyrins has also been widely studied [16][17][18][19][20][21]. It is well-known that these natural macrocycles are reducible through two reversible one-electron transfers between 0 and À2 V vs SCE.…”

Section: Introductionmentioning

confidence: 99%