Covalent organic frameworks (COFs), newly emerging crystalline and porous materials, have been widely studied in many fields because of their unique periodic porous structures, high surface area, and strong interlayer π-π interaction when they are formed into a layered structure. Among the various types of COFs, highly oriented COF thin films with a layered structure have received great attention as one of the most promising organic-based two-dimensional (2D) materials due to their modifiability, flexibility, and multifunctional properties. In this mini-review, we aim to provide information on recent advances in highly oriented 2D COF thin film, which have one molecular thickness level to tens of nanometers. We first discuss the preparation of high-quality 2D COF thin films in terms of interfacial synthesis and exfoliation methods, which are representative methods for bottom-up and top-down approaches, respectively. Also, we summarize the applications of 2D COF thin film focusing on semiconducting devices, membranes, and highly sensitive and selective sensors.
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