Improved photocatalytic hydrogen evolution driven by chloro(terpyridine)platinum(ii) derivatives tethered to a single pendant viologen acceptor

Abstract

Three chloro(4'-(N-methylpyridinium)-2,2':6',2''-terpyridine)platinum(ii) (abbreviated as ) derivatives tethered to a single alkyl viologen unit (-(CH2)n-CH2-N(+)C5H4-C5H4N(+)-CH3; abbreviated as -, where n = 1, 3, and 4), i.e., , have been synthesized and investigated in detail. It is shown that the turnover number (TON) for the photocatalytic H2 evolution from water in the presence of a sacrificial electron donor EDTA (ethylenediaminetetraacetic acid disodium salt) is dramatically improved by the attachment of a single alkyl unit (TON = 21.5-25.2, 12 h). Spectrophotometric studies reveal that the photoirradiation of in the presence of EDTA initially leads to the formation of a 1-electron-reduced species, and then to a 2-electron-reduced species, where reductive quenching of a photoexcited species is a major path to the reduced photoproduct in each step. Electrochemical studies show that two consecutive 1-electron reductions at the unit are nearly overlapped with the corresponding reductions at the unit. The 1-electron-reduced species can be thus expressed as either or , while the 2-electron-reduced one as . Moreover, the latter products behave as stacked species involving three types of π-dimer sites, ()2, ()2, and ()(), and do not drive thermal H2 evolution according to the reaction: + 2H(+) → + H2. The H2 evolution from water photocatalyzed by has been found to occur via formation of 3-electron-reduced species; + EDTA + hν → (or ) + EDTA(ox), and (or ) + 2H(+) → (or ) + H2.

Bacteria‐Triggered Solar Hydrogen Production via Platinum(II)‐Tethered Chalcogenoviologens

“…[14] Recently, several simplified systems were developed with improved turnover number (TON). [15] Particularly for the one-component system using PtL 2 + -MV 2 + , [16] it includes multi-step PET processes and diminishing backward electron transfer (BET) processes, resulting in the rapid regeneration of the PtL 2 + .…”

Two-Electrode Solar Water Splitting Permitting H2 Separation at a Dark Cathode

“…The high HER activity initially found for the amidate-bridged Pt(II) 2 dimers may be similarly explained. As noted earlier, 17 the hydride formation accompanies the formal oxidation at the metal center (i.e., Pt(II) 2  Pt(2.5+) 2 + e -) and therefore the strongly donating property of ligands together with the filled-filled d z2 -d z2 interaction greatly contributes to the thermodynamic stability of the Pt(II)-Pt(III)-H intermedi-ate� Several other groups have so far reported on the results consistent with our conclusion� 28 On the other hand, we also attempted to develop the dyads and triads constructed by the covalent linkage of components selected from WRC, PS, Acceptor, and Donor� [29][30][31][32] The first successful model was a PS-WRC dyad given by the amide coupling of [Ru(bpy) 2 (5amino-phen)] 2+ (phen = 1,10-phenanthroline) and PtCl 2 (dcbpy) (dcbpy = 4,4'-dicarboxy-bpy) (Figure 2), 24 which was turned out to be the first example of a photo-hydrogen-evolving molecular device promoting the water reduction to H 2 in the presence of Donor (EDTA) without any additional components� Based on the photocatalysis experiments combined with the in-situ dynamic light scattering (DLS) measurements, the lack of colloidal platinum formation was clearly evidenced for many of such molecular devices developed in our group� 25,30,31,33 Developing PECs with a dark cathode rather than Tandem PECs As mentioned above, the two-phase gas evolution technique adopted in our molecular-based photoelectrochemical cells (PECs) has a great advantage (Figure 3c). The original concept was developed by Fujishima and Honda in 1972 (Figure 3a).…”

Artificial Photosynthesis: Learning from Nature

“…In the case of the viologen‐containing complexes, the ground state of the photosensitizing site, i.e., PtCl 2 (bpy) was immediately regenerated from its reduced form after the first PET step, thus restoring the light absorption ability (Figure b).As a result, the Pt II bipyridyl complex with four viologen periphery, [PtCl 2 (5,5′‐MV4)] 8+ , recorded one order of magnitude higher TON of 27 after 12 h of photolysis compared to PV 2+ . Further series study was carried out and TONs of 35 and 25.2 were recorded with a Pt II bipyridyl complex and a Pt II terpyridyl complex, respectively. With the same strategy, Ru II ‐based photosensitizers with peripheral methyl viologen units were designed to store and transfer multiple electrons to colloidal Pt WRC.…”