Two-dimensional polymers (2DPs) and their layer-stacked 2D covalent organic frameworks (2D COFs) are classes of structurally defined crystalline polymeric materials with exotic physical and chemical properties. Yet, synthesizing 2DP and 2D COF single crystals via irreversible reactions remains challenging. Here we report the synthesis of charged 2DP (C2DP) single crystals through an irreversible Katritzky reaction, under pH control, on a water surface. The periodically ordered 2DPs comprise aromatic pyridinium cations and counter BF₄⁻ anions. The C2DP crystals, which are composed of linked porphyrin and pyrylium monomers (C2DP-Por), have a tunable thickness of 2–30 nm and a lateral domain size up to 120 μm². Single crystals with a square lattice (a = b = 30.5 Å) are resolved by imaging and diffraction methods with near-atomic precision. Furthermore, the integration of C2DP-Por crystals in an osmotic power generator device shows an excellent chloride ion selectivity with a coefficient value reaching ~0.9 and an output power density of 4 W m⁻², superior to those of graphene and boron nitride.

二维聚合物 (2DP) 及其层状堆叠的 2D 共价有机框架 (2D COF) 是具有特殊物理和化学特性的结构定义的结晶聚合物材料类别。然而，通过不可逆反应合成 2DP 和 2D COF 单晶仍然具有挑战性。在这里，我们报告了在 pH 控制下，在水面上通过不可逆的卡特里茨基反应合成带电 2DP (C2DP) 单晶。周期性排列的 2DP 包含芳香族吡啶鎓阳离子和反相 BF ₄ ^-阴离子。C2DP 晶体由连接的卟啉和吡喃单体 (C2DP-Por) 组成，具有 2-30 nm 的可调厚度和高达 120 μm ²的横向域尺寸。具有方形晶格的单晶（a =  b  = 30.5 Å) 通过成像和衍射方法以近原子精度解析。此外，C2DP-Por 晶体在渗透发电装置中的集成显示出优异的氯离子选择性，系数值达到~0.9，输出功率密度为 4 W m ^-2，优于石墨烯和氮化硼。