On‐Water Surface Synthesis of 2D Conjugated Metal–Organic Framework Films With Controllable Layer Orientation Enabling High‐Performance Chemiresistive Sensing

ABSTRACT

Two‐dimensional conjugated metal–organic frameworks (2D c ‐MOFs) offer an appealing platform for electronic devices, particularly chemiresistive sensors, owing to their unique combination of electrical conductivity and intrinsic porosity. However, their pronounced structural and transport anisotropies render device performance highly sensitive to layer orientation, underscoring the need for synthetic strategies that enable the controlled synthesis of well‐aligned 2D c ‐MOF films. Here, we introduce a surfactant monolayer‐assisted on‑water synthesis that programs the layer orientation of conductive Ni‑HHTP (HHTP = 2,3,6,7,10,11‐hexahydroxytriphenylene) films (face‑on vs. edge‑on) over cm ² ‑scale areas by tuning ligand‐surfactant monolayer electrostatic vs. hydrogen‑bonding interactions. Imaging and scattering techniques unambiguously confirm preferential face‐on and edge‐on layer orientations, while electrical transport and optical pump‐THz probe spectroscopy reveal markedly enhanced intralayer charge transport in face‐on films, motivating their integration into chemiresistive sensing. Chemiresistive NH ₃ sensors based on face‑on Ni‑HHTP films achieve a response of 269.8% at 50 ppm and an ultralow detection limit of 8.45 ppb at room temperature, surpassing edge‑on films and previously reported 2D c ‑MOF sensors. These results establish surfactant‐programmed on‐water synthesis as a new route to macroscopic orientation control in 2D c ‐MOFs, enabling deliberate exploitation of their anisotropic charge transport in high‐performance sensing and electronic devices.