The art of two-dimensional soft nanomaterials

The discovery of graphene has triggered the explosive development of two-dimensional (2D) nanomaterials, including both inorganic and organic species. Benefiting from the simple elemental composition, inorganic 2D nanomaterials were the center research in the past decade, which has long shadowed the research of 2D organic (or soft) nanomaterials. Although many kinds of 2D soft nanomaterials have been successfully prepared, a unified definition for them is still impossible due to the complicate and quite different chemical structures between each other and even relying on totally different techniques to distinguish them. Since our first review on 2D soft nanomaterials in 2015, this field has moved forward with big success. In this review, we will focus on the development of 2D soft nanomaterials after 2015. In order to deliver better overview of this field, new and comprehensive classification is used in this review: 2D aromatic molecules, graphene and graphene nanoribbons, graphyne and graphdiyne, BxCyNz nanosheets, 2D polymers, 2D supramolecules, crystalline 2D assemblies, 2D covalent organic frameworks, 2D metal-organic frameworks, sandwich-like 2D porous polymers, 2D polymer nanosheets, etc. The focus of this review lies on synthetic strategies and the challenges of characterization, definition and fundamental understanding.