Exciton effects play an important role in many polymeric photocatalytic systems, yet to date have largely been neglected in photocatalytic reactions over graphitic carbon nitride (g-CN). Since an exciton consists of a bound electron and hole, strategies that can boost the dissociation of exciton to generate a hot electron and hole should lead to enhanced photocatalytic activity. Herein, by using crystalline porous carbon nitride (CPCN) as a model, we demonstrate that grafting CPCN with electron accumulation capacity can efficiently facilitate the dissociation of exciton. Density functional theory (DFT) calculation shows that the introduced cyano group (-C≡N) in CPCN can distort the structure of carbon nitride and result in an energy disordered interface, thus, the electron in exciton can be extracted by -C≡N and then stabilized by K⁺. Benefited from this electron accumulation process, the exciton in CPCN is effectively dissociated and the formed hot electron and hole is rapidly transferred. Specifically, the average lifespan (τ_ave) is reduced from 3.76 ns (bulk carbon nitride, BCN) to 2.65 ns (CPCN), while the surface charge transfer efficiency (η_t) is increased from 36.6% (BCN) to 50.8% (CPCN). As a result, the obtained CPCN displays excellent performance for photocatalytic molecular oxygen activation. This work sheds light on the development of advanced carbon nitride-based photocatalysts for contaminant degradation and energy conversion through excitonic engineering.