On‐Surface Synthesis of B3N3‐Substituted Two‐Dimensional Covalent Organic Frameworks with Distinct Pore Sizes and Kagome Band Structures

Why It Matters

The ability to tune band structures through atom‑precise BN‑doping opens pathways for next‑generation, metal‑free semiconductors and quantum‑material platforms, accelerating the design of functional low‑dimensional electronics.

Key Takeaways

• B3N3-linked COFs synthesized on Ag(111) and Au(111) surfaces
• Spacer length (biphenyl vs quaterphenyl) tunes band gap and dispersion
• Non‑planar, chiral structure confirmed by STM and AFM imaging
• Site‑selective dehydrogenation locally modifies electronic properties

Pulse Analysis

Covalent organic frameworks have emerged as a versatile platform for engineering porous, crystalline materials whose properties can be dialed in by molecular design. Incorporating borazine (B3N3) units into the backbone introduces heteroatomic sites that mimic the electronic behavior of hexagonal boron nitride while retaining the lightweight, carbon‑rich nature of COFs. This hybridization promises enhanced thermal stability and tunable band gaps, positioning BN‑doped COFs as attractive candidates for flexible electronics, sensing, and optoelectronic applications.

In the reported study, the authors deposited B3N3‑linked monomers onto atomically flat Ag(111) and Au(111) surfaces and induced polymerization under ultra‑high vacuum. Scanning tunneling microscopy and bond‑resolved atomic force microscopy revealed a chiral, non‑planar lattice that deviates from the flat geometry typical of carbon‑only COFs. Photoemission spectroscopy, supported by density‑functional calculations, showed that extending the spacer from biphenyl to quaterphenyl systematically narrows the band gap and increases frontier‑band dispersion, while the B3N3 nodes themselves raise the gap and suppress dispersion relative to carbon analogues. Moreover, targeted dehydrogenation of B3N3 sites locally altered the electronic landscape, demonstrating site‑specific control.

These findings provide a blueprint for designing metal‑free, low‑dimensional semiconductors with programmable electronic structures. By leveraging precise on‑surface synthesis, researchers can now explore a broader palette of heteroatom‑substituted COFs, tailoring properties for quantum‑confined devices, spintronic platforms, and catalytic interfaces. The ability to modulate band topology through simple chemical modifications accelerates the transition from laboratory prototypes to scalable, application‑ready materials in the emerging field of atomically engineered nanotechnology.