Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ~1.5 µm), the reported thin‐film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate an efficient synthesis of crystalline two‐dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF‐PP or 2D BECOF‐PN ) by employing a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF‐PP is featured as free‐standing thin film with large single‐crystalline domains up to ~60 µm 2 and tunable thickness from 6 to 16 nm. The molecular‐level structures are clearly resolved by high‐resolution transmission electron microscopy (HR‐TEM) and selected‐area electron diffraction (SAED) which are supported by density functional theory (DFT) calculation. Due to the high crystallinity, facile thin‐film processability, high mechanical stability as well as the incorporation of electroactive porphyrin monomers, a hybrid memory device composed of 2D BECOF‐PP film on silicon nanowire‐based field‐effect transistor is demonstrated as a bio‐inspired system to mimic neuronal synapses, displaying a learning‐erasing‐forgetting memory process. Pulsed voltage input induces the polarization of the film that is critical to emulate the potentiation of the neuronal membrane. This work paves the way to develop highly crystalline 2D COF thin film as an easy‐to‐fabricate active component applicable for CMOS‐compatible neuromorphic computing.
