Directed trilithiation enables entropically stabilized heavy-atom-centered triangulenes.

Embedding heavy main-group elements at the core of rigid π-conjugated frameworks is an ideal strategy to achieve stability through geometric confinement, yet its realization has remained synthetically elusive. Here we show that a directed, regioselective trilithiation strategy enables controlled incorporation of heavy elements into triangulene frameworks. Using nitrogen-bridged macrocycles as precursors, antimony-, bismuth-, tin-, and lead-centered triangulenes were synthesized. Single-crystal X-ray analyses reveal exceptionally deep bowl-shaped geometries and one-dimensional columnar assemblies. Despite highly strained bonding environments, these compounds exhibit remarkable thermal and chemical stability, highlighting the effectiveness of entropic stabilization arising from the rigid structural confinement system. Moreover, the antimony-centered triangulene undergoes reversible and controllable redox transformation between trivalent and pentavalent states through chelation and coordination effects, demonstrating how topological embedding translates into distinct functional behavior. This work establishes a general synthetic platform for heavy-atom embedding in curved π-systems and opens opportunities for design of unique main-group architectures.