Light-driven water splitting is a potential source of abundant, clean energy, yet efficient charge-separation and size and position of the bandgap in heterogeneous photocatalysts are challenging to predict and design. Synthetic attempts to tune the bandgap of polymer photocatalysts classically rely on variations of the sizes of their π-conjugated domains. However, only donor-acceptor dyads hold the key to prevent undesired electron-hole recombination within the catalyst via efficient charge separation. Building on our previous success in incorporating electron-donating, sulphur-containing linkers and electron-withdrawing, triazine (C3 N3 ) units into porous polymers, we report the synthesis of six visible-light-active, triazine-based polymers with a high heteroatom-content of S and N that photocatalytically generate H2 from water: up to 915 μmol h-1 g-1 with Pt co-catalyst, and-as one of the highest to-date reported values -200 μmol h-1 g-1 without. The highly modular Sonogashira-Hagihara cross-coupling reaction we employ, enables a systematic study of mixed (S, N, C) and (N, C)-only polymer systems. Our results highlight that photocatalytic water-splitting does not only require an ideal optical bandgap of ≈2.2 eV, but that the choice of donor-acceptor motifs profoundly impacts charge-transfer and catalytic activity.

Department of Organic Chemistry Charles University Hlavova 8 128 43 Prague 2 Czech Republic

Faculty of Science Department of Physical and Macromolecular Chemistry Charles University Hlavova 8 128 43 Prague 2 Czech Republic

Humboldt Universität zu Berlin Department of Chemistry Brook Taylor Str 2 12489 Berlin Germany

Institute of Chemistry Technische Universität Berlin Hardenbergstraße 40 10623 Berlin Germany

Institute of Organic Chemistry and Biochemistry of the CAS Flemingovo nám 2 166 10 Prague 6 Czech Republic

Leibniz Institut für Polymerforschung Dresden e 5 Institute of Physical Chemistry and Polymer Physics Hohe Str 6 01069 Dresden Germany

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