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.