All‐or‐Nothing Cooperative Self‐Assembly of an Annulene Sandwich

Ring-fenced: A 14-component assembly is formed by coordinating 1,4-diazabicyclo[2.2.2]octane (DABCO) to a [12]porphyrin nanoring. The 24 zinc–nitrogen interactions in this sandwich complex lock each conjugated macrocycle into a planar conformation, dramatically sharpening the near-IR absorption band. This result highlights the scope of double-strand formation as a way of creating nano-objects with well-defined shapes.