The　systematic　alteration　of　a　carbon　nitride　unit　(CNU)　for　visible　light　photocatalytic　water　splitting　is　a　promising　research　subject　owing　to　the　increasingly　serious　energy　and　environmental　complications.　Herein,　the　conjugated　monomer　3,6-dibromopyridazine　(DBP)　is　integrated　within　polymeric　carbon　nitride　(PCN　named　as　CNU　=　carbon　nitride　containing　urea　precursor)　via　thermal　condensation,　which　is　designated　as　CNU-DBP.　These　samples　are　used　for　the　first　time　in　the　photocatalytic　conversion　of　CO2　reduction　and　hydrogen　(H2)　evolution　through　water　splitting.　Such　integration　intimidates　the　electron　density,　promoting　charge　transfer　separation　and　elevating　the　photocatalytic　activity　of　CNU　under　visible　light　illumination.　The　superior　sample　such　as　CNU-DBP9.0　after　4　h　of　photooxidation　generates　65.7　μmol　of　CO　and　17.3　μmol　of　H2　of　the　reaction　system,　emphasizing　the　highest　photocatalytic　activity.　The　H2　evolution　rate　(HER)　for　pristine　CNU　is　found　as　11.9　μmol　h−1,　whereas　for　CNU-DBP9.0　it　is　estimated　at　178.2　μmol　h−1　with　15　times　greater　activity.　This　process　predicts　a　significant　diversion　in　the　specific　area,　bandgap,　and　chemical　composition　and　promotes　the　efficient　separation　of　photogenerated　charge　carriers　from　the　ground　state　to　the　excited　state　of　CNU,　thereby　considering　it　a　best　candidate　for　the　photoreduction　of　CO2　source　and　water　splitting　into　H2.　©　2021　Wiley-VCH　GmbH