Wet Transfer of In Situ Grown Azo-Containing Two-Dimensional Conjugated Covalent Organic Framework Films for Photoswitchable Electronic Devices.

Two-dimensional π-conjugated covalent organic frameworks (2D π-COFs) combine in-plane π-delocalization with periodic open channels, making them versatile platforms for integrating functional groups into optoelectronic and neuromorphic systems. However, their predominant powder form has fundamentally constrained device integration and interfacial engineering. Herein, we demonstrate a general strategy for constructing high-quality transition-metal chalcogenide@2D π-COF van der Waals heterostructures (vdWHs). Large-area, atomically flat 2D π-COF films are first grown on SiO2 substrates via a liquid-solid interfacial reaction and subsequently transferred onto monolayer MoS2 through a mild in situ wet-transfer process. The resulting COF films exhibit atomic-scale flatness and form clean interfaces, promoting efficient interfacial charge transfer in COF@MoS2 heterojunctions. As a model system, we employ a robust imidazole-linked 2D π-COF (COF-Azo) functionalized with azobenzene moieties, whose reversible trans-cis photoisomerization dynamically modulates the heterojunction's electronic structure. The COF-Azo@MoS2 devices display pronounced and reversible photoswitching behavior, achieving a carrier density modulation of ∼6.7 × 1011 cm-2 and an on-state current variation of ∼43.7%. Importantly, optical control over the isomerization fraction enables non-volatile memory behavior within the vdWHs. This work establishes a scalable route to atomically flat 2D π-COF films as viable building blocks for vdW heterostructures and introduces a robust platform for optically reconfigurable optoelectronics and memory devices.