Sub-1 nm Materials Chemistry: Challenges and Prospects.

Subnanometer materials (SNMs) refer to nanomaterials with a feature size close to 1 nm, similar to the diameter of a single polymer, DNA strand, and a single cluster/unit cell. The growth and assembly of subnanometer building blocks can be controlled by interactions at atomic levels, representing the limit for the precise manipulation of materials. The size, geometry, and flexibility of 1D SNMs inorganic backbones are similar to the polymer chains, bringing excellent gelability, adhesiveness, and processability different from inorganic nanocrystals. The ultrahigh surface atom ratio of SNMs results in significantly increased surface energy, leading to significant rearrangement of surface atoms. Unconventional phases, immiscible metal alloys, and high entropy materials with few atomic layers can be stabilized, and the spontaneous twisting of SNMs may induce the intrinsic structural chirality. Electron delocalization may also emerge at the subnanoscale, giving rise to the significantly enhanced catalytic activity. In this perspective, we summarized recent progress on SNMs, including their synthesis, polymer-like properties, metastable phases, structural chirality, and catalytic properties, toward energy conversion. As a critical size region in nanoscience, the development of functional SNMs may fuse the boundary of inorganic materials and polymers and conduce to the precise manufacturing of materials at atomic levels.