Hydrophilicity Control of Visible-Light Hydrogen Evolution and Dynamics of the Charge-Separated State in Dye/TiO2/Pt Hybrid Systems

Visible‐light‐driven H2 evolution based on Dye/TiO2/Pt hybrid photocatalysts was investigated for a series of (E)‐3‐(5′‐{4‐[bis(4‐R1‐phenyl)amino]phenyl}‐4,4′‐(R2)2‐2,2′‐bithiophen‐5‐yl)‐2‐cyanoacrylic acid dyes. Efficiencies of hydrogen evolution from aqueous suspensions in the presence of ethylenediaminetetraacetic acid as electron donor under illumination at λ>420 nm were found to considerably depend on the hydrophilic character of R1, varying in the order MOD (R1=CH3OCH2, R2=H)≈MO4D (R1=R2=CH3OCH2)>HD (R1=R2=H)>PD (R1=C3H7, R2=H). In the case of MOD/TiO2/Pt, the apparent quantum yield for photocatalyzed H2 generation at 436 nm was 0.27±0.03. Transient absorption measurements for MOD‐ or PD‐grafted transparent films of TiO2 nanoparticles dipped into water at pH 3 commonly revealed ultrafast formation (