Synthesis of Five-Porphyrin Nanorings by Using Ferrocene and Corannulene Templates

The smallest and most strained member of a family of π‐conjugated cyclic porphyrin oligomers was synthesized by using pentapyridyl templates based on ferrocene and corannulene. Both templates are effective for directing the synthesis of the butadiyne‐linked cyclic pentamer, despite the fact that the radii of their N5 donor sets are too small by 0.5 Å and 0.9 Å, respectively (from DFT calculations). The five‐porphyrin nanoring exhibits a structured absorption spectrum and its fluorescence extends to 1200 nm, reflecting strong π conjugation and Herzberg–Teller vibronic coupling. Gerade groß genug: Zwei Template wurden für die Bildung eines π‐konjugierten cyclischen Porphyrinpentamers getestet. 1,3,5,7,9‐Penta(4‐pyridyl)corannulen war effektiver als ein Ferrocen‐basiertes Templat, obwohl der Radius seines N5‐Ligandensatzes fast 1 Å zu klein für den Hohlraum des Nanorings ist.