Organic two-dimensional crystals (O2DCs) are a class of synthetic layered materials, typically constructed from π-conjugated building blocks, that show extended in-plane π-conjugation and/or interlayer electronic couplings. They are synthesized either directly as monolayer to few-layer nanosheets or as bulk crystals that can be exfoliated. O2DCs display customizable topological structures and layer-dependent physical attributes, offering a versatile material platform for exploring intriguing electronic and quantum phenomena. In this Review, we discuss the structure–property relationships and synthetic strategies of O2DCs, with particular emphasis on their unique electronic structures, charge transport properties and the emergence of quantum states, such as topological and superconducting phases, alongside different spin states. Furthermore, we highlight emerging device applications of O2DCs across electronics, optoelectronics and spintronics. Finally, we provide an outlook on the persistent challenges in synthetic chemistry, physics and materials science that must be addressed to further advance this field.

有机二维晶体 （O2DC） 是一类合成的层状材料，通常由π共轭构建单元构成，显示出扩展的面内 π 共轭和/或层间电子耦合。它们可以直接合成为单层到几层纳米片，也可以合成为可以剥离的块状晶体。O2DC 显示可定制的拓扑结构和与层相关的物理属性，为探索有趣的电子和量子现象提供了一个多功能的材料平台。在这篇综述中，我们讨论了 O2DC 的结构-性质关系和合成策略，特别强调了它们独特的电子结构、电荷传输性质和量子态的出现，例如拓扑和超导相，以及不同的自旋态。此外，我们重点介绍了 O2DC 在电子、光电子和自旋电子学中的新兴器件应用。最后，我们展望了合成化学、物理学和材料科学中必须解决的持续挑战，以进一步推动该领域的发展。