The　polarity　of　a　semiconducting　molecule　affects　its　intrinsic　photophysical　properties,　which　can　be　tuned　by　varying　the　molecular　geometry.　Herein,　we　developed　a　D3h-symmetric　tricyanomesitylene　as　a　new　monomer　which　could　be　reticulated　into　a　vinylene-linked　covalent　organic　framework　(g-C54N6-COF)　via　Knoevenagel　condensation　with　another　D3h-symmetric　monomer　2,4,6-tris(4′-formyl-biphenyl-4-yl)-1,3,5-triazine.　Replacing　tricyanomesitylene　with　a　C2v-symmetric　3,5-dicyano-2,4,6-trimethylpyridine　gave　a　less-symmetric　vinylene-linked　COF　(g-C52N6-COF).　The　octupolar　conjugated　characters　of　g-C54N6-COF　were　reflected　in　its　scarce　solvatochromic　effects　either　in　ground　or　excited　states,　and　endowed　it　with　more　promising　semiconducting　behavior　as　compared　with　g-C52N6-COF,　such　as　enhanced　light-harvesting　and　excellent　photo-induced　charge　generation　and　separation.　Along　with　the　matched　energy　level,　g-C54N6-COF　enabled　the　two-half　reactions　of　photocatalytic　water　splitting　with　an　average　O2　evolution　rate　of　51.0　μmol　h−1　g−1　and　H2　evolution　rate　of　2518.9　μmol　h−1　g−1.　Such　values　are　among　the　highest　of　state-of-the-art　COF　photocatalysts.　©　2020　Wiley-VCH　GmbH