In nature, the diverse functions of proteins and DNA are often dictated by their distinct folding and interlocking patterns. Even minor structural variations can have a profound functional impact. Given its significant potential in life sciences, this area merits in-depth exploration. In recent years, diverse construction strategies have enabled the synthesis of a wide array of intricate supramolecular complexes. The 8 18 knot, closed three-link chain, and multiply folded assembly are extremely rare topologies, and obtaining these complexes via subtle modulation of building blocks is exceedingly difficult.
To address this challenge, a research team led by Assoc. Prof. Lilong Dang from Luoyang Normal University adopted a coordination-angle-controlled strategy. By utilizing two carbazole-based ligands featuring distinct bite angles, they achieved the precise construction of both interlocked and non-interlocked architectures through coordination-driven self-assembly. This significant work was published in National Science Review in July 2026, with Assoc. Prof. Lilong Dang, M.Sc. Xiaoqian Wan, and Ph.D. candidate Jianxin Yang serving as co-first authors.
Two bidentate pyridine ligands ( L1 and L2 ) with distinct coordination angles were synthesized via Suzuki coupling of 4-pyridylboronic acid pinacol ester with 3,6-dibromocarbazole and 2,7-dibromocarbazole, respectively. Assembly of these ligands with metal building blocks of different sizes and conjugation properties successfully afforded a molecular-tweezer-like compound, a snowflake-shaped folded assembly, an 8 18 knot, and a closed three-link chain.
SC-XRD analysis confirmed that the molecular-tweezer-like compound adopts a stable architecture, stabilized by face-to-face π-π stacking between the carbazole units of two U-shaped metallamacrocycles. In contrast, the snowflake-shaped folded assembly emerges through cooperative interactions, including multiple π-π stacking between half-sandwich rhodium building blocks and carbazole moieties, as well as the structural templating provided by the rhodium sandwich complexes.
The large-angle coordination geometry of ligand L2 plays a pivotal role in stabilizing both the 8 18 knot and the closed three-link chain. The formation of the 8 18 knot is driven by non-covalent interactions between L2 and the building block E1 (OTf) 2 , which induce the folding and self-entanglement of a single molecular strand. In contrast, the closed three-link chain arises through coordination-directed self-assembly of E2 (OTf) 2 and L2 , wherein the resulting metallamacrocycle undergoes conformational twisting to adopt an interlocked topology.
Subsequently, the photophysical properties of the 8 18 knot and the closed three-link chain were investigated. Their favorable absorption characteristics prompted further study of their photothermal conversion performance. Intramolecular π-π stacking interactions, acting synergistically with half-sandwich metal fragments, enhance non-radiative relaxation and suppress radiative relaxation, thereby effectively dissipating excitation energy as heat. EPR measurements revealed changes in signal intensity before and after irradiation, indicating the generation of unpaired electrons. The variation in radical content was positively correlated with photothermal conversion efficiency, suggesting that organic radicals also play a key role in modulating photothermal performance.
This synthetic strategy not only provides a viable pathway for the design and construction of higher-order mechanically interlocked topological architectures, but also establishes a novel platform for developing functional materials with exceptional photothermal conversion properties.
National Science Review
Experimental study