Ultra-thin two-dimensional (2D) organic semiconductors are promising candidates for photocatalysts because of the short charge diffusion pathway and favorable exposure of active sites plus the versatile architecture. Nonetheless, the inherent dielectric confinement of 2D materials will induce a strong exciton effect hampering the charge separation. Herein, we demonstrated an effective way to reduce the dielectric confinement effect of 2D ionic covalent organic nanosheets (iCONs) by tailoring the functional group via molecular engineering. Three ultra-thin CONs with different functional groups and the same ionic moieties were synthesized through Schiff base condensation between ionic amino monomer triaminoguanidinium chloride (TG) and aldehyde linkers. The integration of the hydroxyl group was found to significantly increase the dielectric constant by enhancing the polarizability of ionic moieties, and thus reduced the dielectric confinement and the corresponding exciton binding energy (E_b). The champion hydroxyl-functional iCON exhibited promoted exciton dissociation and in turn a high photocatalytic hydrogen production rate under visible-light irradiation. This work provided insights into the rationalization of the dielectric confinement effect of low-dimensional photocatalysts.

超薄二维 (2D) 有机半导体因其电荷扩散路径短、活性位点的良好暴露以及多功能结构而成为光催化剂的有前途的候选者。尽管如此，二维材料固有的介电限制会引起强烈的激子效应，从而阻碍电荷分离。在此，我们展示了一种通过分子工程定制官能团来降低二维离子共价有机纳米片 (iCON) 的介电限制效应的有效方法。通过离子型氨基单体三氨基胍氯化物 (TG) 与醛基之间的席夫碱缩合，合成了三种具有不同官能团和相同离子基团的超薄 CON。Eb _）。冠军羟基功能 iCON 表现出促进的激子解离，进而在可见光照射下具有高光催化产氢率。这项工作为低维光催化剂的介电限制效应的合理化提供了见解。