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Platinum(II) Terpyridyl Acetylide Complexes on Platinized TiO2: Toward the Photogeneration of H2 in Aqueous Media

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journal contribution
posted on 19.10.2009, 00:00 by Paul Jarosz, Pingwu Du, Jacob Schneider, Soo-Hyun Lee, David McCamant, Richard Eisenberg
New platinum(II) terpyridyl acetylide complexes having the ability to bind to TiO2 have been synthesized and assayed in their ability to sensitize platinized titanium dioxide for the photogeneration of H2 using visible light (λ > 410 nm). Specifically, the complexes [Pt(tpy-phen-COOH)(CC−C6H5)]Cl (1), where tpy-phen-COOH = 4′-(4-carboxyphenyl)-[2,2′;6′,2′′]terpyridine and CC−C6H5 = phenylacetylide, and [Pt(tpy-COOH)(CC−C6H5)]Cl (2), where tpy-COOH = 4′-carboxy-2,2′;6′,2′′-terpyridine, were prepared to investigate the effectiveness of attachment and proximity to the TiO2 surface on hydrogen yield. Both complexes 1 and 2 sensitize the photogeneration of hydrogen, but produce fewer turnovers than the unbound chromophore, [Pt(ttpy)(CC−C6H5)]PF6 (5). On the basis of these observations and electrochemical data, a major limitation to the effectiveness of these chromophores is their instability upon oxidation. To attempt to remedy this problem, two donor-chromophore (D-C) dyads, [Pt(tpy-phen-COOH)(CC−C6H4CH2−PTZ)]PF6 (3), where CC−C6H4CH2−PTZ = N-(4-ethynylbenzyl)-phenothiazine and [Pt(tpy-COOH)(CC−C6H4CH2−PTZ)]Cl (4) were prepared to function as TiO2-attached sensitizers. Transient absorption measurements have shown that the PTZ moiety reductively quenches the Pt center in several picoseconds. While the resultant PTZ+ radical cation is capable of oxidizing rapidly the triethanolamine sacrificial electron donor, dyads 3 and 4 attached to platinized TiO2 do not function to generate hydrogen upon irradiation, in contrast with results seen for 1 and 2.