▎ 摘　　要

The electronic properties of finite-sized graphene fragments are strongly dependent on their topological structures. The existence of two or more extended zigzag edges could lead to unique open-shell character and magnetic activity. In this review, various types of well-defined graphene nanoribbons, nanographenes, and graphene-like molecules with open-shell character are summarized. Particularly, chemistry and electronic properties of graphene fragments with one, two, and three pairs of parallel zigzag edges, zethrenes with quinoidal structures, and [n]triangulenes with three zigzag edges are discussed in detail. Synthesis of this kind of open-shell molecules is very challenging, and both solution-phase and on-surface chemistry have been used. Their radical characters can be simply predicted in terms of Clar's sextets and quantitatively analyzed by spin-unrestricted density functional theory or multireference quantum mechanical calculations. Their unique magnetic activity and quantum properties would render them promising materials for all carbon-based spintronic and quantum devices.