Research　based　on　the　full　water　splitting　via　heterogenous　semiconducting　photocatalyst　is　a　significant　characteristic　nevertheless　challenging　for　determining　the　energy　and　environmental　crises.　With　respect　to　this,　a　photocatalytic　water　splitting　by　visible　light　through　heterojunction　semiconductors　has　been　anticipated　as　a　route　to　the　sustainable　energy.　For　the　first　time,　we　integrate　a　potential　conjugated　donor-acceptor　(DA)　co-monomer　such　as　2,　3-dichloroquinoxaline　(DCQ)　within　the　structure　of　polymeric　carbon　nitride　(PCN)　by　a　facile　one-pot　co-polymerization　process.　The　DCQ　which　is　acting　as　an　organic　motif　that　simulates　a　nucleophilic　attack　on　the　hosting　PCN　semiconductor　which　extends　into　a　long　chain　of　the　polymer　having　enormous　surface　area　and　remarkable　photocatalytic　activity　for　H-2　and　O-2　evolution　as　compared　to　the　parental　CNU.　The　supremacy　of　molecular　geometry　with　DA　ratio　is　effectively　studied　by　absorbent,　calculated　band　gap　and　migration　of　electrons　on　the　photocatalytic　performance　of　as-synthesized　CNU-DCQx　co-polymer.　The　density　functional　theory　(DFT)　calculation　deliver　supplementary　evidence　for　the　positive　incorporation　of　DCQ　in　to　the　PCN　matrix　with　reduced　band　gap　upon　copolymerization.　Further,　the　hydrogen　evolution　rate　(HER)　for　pure　CNU　with　14.2　mu　mol/h　while　for　CNU-DCQ(18.0)　it　is　estimated　at　124.9　mu　mol/h　which　remarkably　fueled　almost　eight　times　more　than　blank　sample.　Similarly,　the　oxygen　evolution　rate　(OER)　analysis　indicates　the　production　0.2　mu　mol/h　(visible)　and　1.5　mu　mol/h　(non-visible)　for　CNU.　However,　the　OER　of　copolymerized　CNU-DCQ(18.0)　is　found　to　be　1.9　mu　mol/h　(visible)　and　12.8　mu　mol/h　(non-visible)　which　almost　nine　times　higher　than　parental　CNU.　Hence,　the　output　of　this　work　reflects　as　an　important　step　on　the　way　to　tailor-designed　and　elucidate　the　promising　role　of　D-pi-A　system　for　the　rational　motifs　of　productive　photocatalysts　for　forthcoming　request.　(C)　2019　Elsevier　Inc.　All　rights　reserved.