To　counteract　the　unwanted　quantum　confinement　effect　and　less　efficient　electron　screening　in　low　dimensional　carbon　nitride,　fusion　of　aromatic　motifs　into　conjugated　carbon　nitride　nanosheets　has　been　developed.　This　results　in　a　red-shift　of　the　optical　absorption　and　an　improved　charge　separation　in　the　polymer　semiconductor,　establishing　a　quantum　efficiency　of　8.8%　at　420　nm　for　H2　generation.　This　journal　is　©　the　Partner　Organisations　2014.