charge carriers, such as morphological control, [10][11][12] elemental doping, [13,14] molecular engineering, [15,16] and heterostructure construction. [17][18][19] In particular, molecular engineering is a rather effective method to regulate the chemical composition and electronic structure of CN.Efforts have been devoted to building organic conjugated copolymers with donor-acceptor system to improve the charge mobility in organic photovoltaic field. [20,21] As such, it is supposed that the construction of intramolecular D-A conjugated copolymers could be a helpful strategy to increase the photocatalytic performance of polymeric photocatalysts. Generally, the D-A conjugated copolymers could be synthesized through the copolymerization between electron donor and acceptor units. The introduction of donor or acceptor units could extend π-conjugated system and induce the intramolecular charge transfer of D-A conjugated copolymers under internal electric field, which help to facilitate the dissociation of photogenerated electrons and holes. [22][23][24][25] Moreover, the construction of D-A structure could flexibly regulate the band structure of conjugated copolymers through the pushpull effect on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), [22,26,27] narrowing the bandgap of copolymers toward extended visiblelight absorption. For instance, Fan et al. fabricated a range of aromatics-incorporation g-C 3 N 4 -based D-A copolymer via nucleophilic substitution reactions and proposed the concept of intramolecular charge transfer transition to clarify the photo catalytic mechanism upon long-wavelength-light illumination. [24] Creatinine-derived moiety as donor unit was also incorporated into melem by copolymerization of creatinine and urea to broaden the absorption range and promote the charge spatial separation. [28] Chen et al. integrated π-deficient pyridine group with carbon nitride skeleton to modulate the electron structure, enabling tunable bandgap and boosted carrier migration. [29] Herein, modified CN-based conjugated copolymers with D-A structure were obtained by thermal copolymerization of 2-aminobenzimidazole (abIM) and urea (Figure 1a). [30,31] abIM was chosen as the reactant and serves as electron acceptor unit due to its high electron affinity. As expected, the as-prepared D-A polymeric photocatalysts with adjustable bandgap exhibit larger surface area, stronger visible-light absorption and faster charge carrier separation as compared to pristine CN. The photocatalytic hydrogen evolution rate of the optimal sample is 2566 µmol g −1 h −1 , which is ≈2.7 times that of pristine CN.The construction of conjugated copolymers with a donor-acceptor (D-A) system has emerged as a promising strategy for improving photocatalytic activity. Herein, a donor-acceptor modified carbon nitride (CN) conjugated copolymer is fabricated via facile thermal copolymerization of 2-aminobenzimidazole (abIM) and urea. The experimental results demonstrate that the abIM units are successful...

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