Conjugated　polymers　(CPs)　are　emerging　and　appealing　light　harvesters　for　photocatalytic　water　splitting　owing　to　their　adjustable　band　gap　and　facile　processing.　Herein,　we　report　an　advanced　mild　synthesis　of　three　conjugated　triazine-based　polymers　(CTPs)　with　different　chain　lengths　by　increasing　the　quantity　of　electron-donating　benzyl　units　in　the　backbone.　Varying　the　chain　length　of　the　CTPs　modulates　their　electronic,　optical,　and　redox　properties,　resulting　in　an　enhanced　performance　for　photocatalytic　oxygen　evolution,　which　is　the　more　challenging　half-reaction　of　water　splitting　owing　to　the　sluggish　reaction　kinetics.　Our　results　could　stimulate　interest　in　these　functional　polymers　where　a　molecular　engineering　strategy　enables　the　production　of　suitable　semiconductor　redox　energetics　for　oxygenic　photosynthesis.　©　2018　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim