Abstract: Edge states—localized electronic states at the boundaries of a material—are often attributed to structural defects or topological features in crystalline solids. In finite 𝜋-conjugated systems such as graphene nanoribbons, boron nitride, and short segments of single-walled carbon nanotubes, these edge states can lead to electron scattering and fluorescence quenching. Computational studies have shown that certain chemical modifications, such as tailored edge-passivation and fullerene-end capping, can suppress these states. However, the origin of edge stages in these finite systems remains poorly understood. Here, we apply Clar’s aromatic sextet theory—a conceptual framework developed by Erich Clar for describing the electronic structure of polycyclic aromatic hydrocarbons—to build an intuitive molecular picture of edge states in finite nanotubes. Although Clar theory has previously been used to model the bonding patterns of infinitely long nanotubes, applying it to finite systems poses a challenge due to ambiguities in selecting a primitive Clar cell, which can lead to different edge structures. We address this issue by developing an algorithm that constructs a definite Clar cell for any nanotube chirality. Notably, the resulting molecular models are not only energetically more stable than their isomers but also intrinsically free of the edge states commonly observed in unit-cell-based models. This work clarifies the molecular origin of edge states and suggests the possibility of designing nanocarbons with bulk-like electronic and optical properties.
Pizza and drinks will be served after the seminar in ATL 2117.