Crystallinity-Oriented Synthetic Approaches to Organic 2D Polymer Networks

Conspectus Since the discovery and rise of graphene, polymers that feature regular two-dimensional (2D) network structures have garnered significant attention. Compared to their inorganic counterparts, however, the development of crystalline organic 2D polymers is still in its early stages. Despite this, organic 2D polymers exhibit substantial promise owing to their long-range ordered topological structures, which can be tuned to offer customizable electronic properties and unique anisotropic physicochemical characteristics. These properties make them ideal candidates for various applications, such as energy storage systems, electronic devices, photocatalysis, and separation membranes. However, the synthesis of crystalline organic 2D polymers presents considerable challenges. Traditional organic polymerization methods are often hindered by factors such as kinetic irreversibility and the anisotropy of intermolecular forces. These limitations result in products that tend to be amorphous or polycrystalline in nature, which makes it difficult to achieve atomically precise 2D single-crystal structures. The core challenge lies in balancing the reversibility of dynamic covalent bonds with the topological control of the polymerization pathway. Moreover, overcoming the entropy-driven tendency of molecular precursors to adopt disordered 3D aggregates rather than an ordered 2D arrangement presents an additional challenge. As a result, the development of novel synthetic strategies to precisely create single-crystalline organic 2D polymer networks has become a leading topic at the cutting edge of both chemistry and materials science. This Account focuses on the progress in constructing crystalline organic 2D polymer networks using three major strategies: solution-phase synthesis, interfacial synthesis, and solid-state synthesis. It systematically reviews their design principles, technical advancements, and challenges, and it briefly discusses the structure–property relationships. For solution-phase synthesis, the combination of solvent polarity modulation and dynamic covalent chemistry enables the ordered assembly of molecular precursors. This method is conceptually simple and amenable to scale-up; however, in practice, achieving high crystallinity requires precise control over solvation effects and reaction kinetics to prevent disordered aggregation. For interfacial synthesis, the confinement effect at the gas–liquid or liquid–liquid interface can be utilized to reduce the degrees of freedom of molecular motion and promote 2D-oriented growth. The key to this strategy is the precise regulation of interfacial tension and the matching of substrate surface symmetry, but large-scale preparation still faces challenges. For solid-state synthesis, 2D networks are directly generated within the crystal precursors through topochemical polymerization. This strategy can effectively avoid solvent interference, but the design of monomers with preorganized conformations is needed, and minor fluctuations in reaction conditions can easily lead to defect proliferation. Furthermore, this Account compares the differences of each strategy in terms of crystallinity control and functionalization compatibility. We anticipate that this Account will offer a deep understanding of the synthesis of crystalline organic 2D polymer networks and stimulate further development in this emerging field.