Conjugated　monomer　2,6-dimethylindole　(DMI)　was　integrated　into　the　triazine　framework　of　polymeric　carbon　nitride　(PCN)　via　molecular　engineering.　As-prepared　samples　were　utilized　for　photocatalytic　evolution　of　hydrogen　(H2)　through　water　splitting　and　photodegradation　of　RhB　dye　under　visible　light.　The　integration　of　this　monomer　DMI　has　been　dominated　within　the　internal　framework　of　PCN　and　operated　as　a　substitution　reaction　membrane,　retarding　an　appropriate　control　and　promote　the　charge　density　in　π-electron　conjugated　system.　It　also　promotes　the　charge　transferring　and　separation　to　elevate　the　photocatalytic　activity　of　PCN　under　visible　light.　The　HER　for　pure　PCN　was　found　as　77.9　μmol/h,　while　for　PCN-DMI18.0　was　predicted　at　701.2 μmol/h,　which　is　exclusively　output　approximately　nine　times　higher　than　that　of　pure　PCN　respectively.　Besides,　the　pseudo-order　kinetic　constant　of　PCN-DMI18.0　degradation　of　RhB　was　multiple　times　higher　when　contrasted　to　pristine　PCN.　©　2021　John　Wiley　&　Sons　Ltd.