The　search　for　metal-free　organic　photocatalysts　for　H2production　from　water　using　visible　light　remains　a　key　challenge.　Reported　herein　is　a　molecular　structural　design　of　pure　organic　photocatalysts,　derived　from　conjugated　polybenzothiadiazoles,　for　photocatalytic　H2evolution　using　visible　light.　By　alternating　the　substitution　position　of　the　electron-withdrawing　benzothiadizole　unit　on　the　phenyl　unit　as　a　comonomer,　various　polymers　with　either　one-　or　three-dimensional　structures　were　synthesized　and　the　effect　of　the　molecular　structure　on　their　catalytic　activity　was　investigated.　Photocatalytic　H2evolution　efficiencies　up　to　116　μmol　h−1were　observed　by　employing　the　linear　polymer　based　on　a　phenyl-benzothiadiazole　alternating　main　chain,　with　an　apparent　quantum　yield　(AQY)　of　4.01　%　at　420　nm　using　triethanolamine　as　the　sacrificial　agent.　©　2016　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim