Photcatalytic HER perfomances of the materials. The series of CTFs synthesized in this work was employed as photocatalysts in sacrificial water splitting under visible light irradiation (>395 nm) using Pt as co-catalyst. The deposition of Pt is generally considered not to affect the photophysical properties of the organic photocatalyst, but to facilitate H 2 elimination from the materials surface. Within the series, CTF-02-Bpy 0.66 showed the highest activity, reaching 7.2 mmol/h/g cat , while all other catalysts show activities between 3.2 and 4.7 mmol/h/g cat (Figure ). The trend of the HER activity cannot be pinpointed to one property alone, but rather to the sum of all optical and photo physical properties. For example, the performance of CTF-02-Bpy is rather low, despite its small band gap and excellent charge separation ability. This is most likely caused by the positioning of the valence band, making the reductive quenching kinetically least favored (Figure ). Also, the rather high HER activity (4.3 mmol/h/g cat ) for the biphenyl-based CTF-02 cannot be explained by its optical and photo physical properties alone. As CTF-02 is the pure biphenylbased polymer in the series, it possesses the weakest water wettability, as confirmed by water vapor physisorption experiments, with a degree of pore filling well below 1 (Table ).