Owing　to　the　large　exciton　binding　energy　(＞100　meV)　of　most　organic　materials,　the　process　of　exciton　dissociation　into　free　electrons　and　holes　is　seriously　hindered,　which　plays　a　key　role　in　the　photocatalytic　system.　In　this　study,　a　series　of　chalcogen　(S,　Se)-substituted　mesoporous　covalent　organic　frameworks　(COFs)　have　been　synthesized　for　enhanced　photocatalytic　organic　transformations.　Photoelectrochemical　measurements　indicate　that　the　introduction　of　semi-metallic　Se　atom　and　the　enlargement　of　conjugation　degree　can　not　only　reduce　the　exciton　binding　energy　accelerating　the　charge　separation,　but　also　reduce　the　band　gap　of　COFs.　As　a　result,　the　COF-NUST-36　with　the　lowest　exciton　binding　energy　(39.5　meV)　shows　the　highest　photocatalytic　performance　for　selective　oxidation　of　amines　(up　to　98%　Conv.　and　97.5%　Sel.).　This　work　provides　a　feasible　method　for　designing　COFs　with　high　photocatalytic　activity　by　adjusting　exciton　binding　energy.　©　2023