Pyrrole Annulation Controls Protonation-Induced Topology Switching in π-Extended Core-Modified Figure-of-Eight Hexaphyrins

Two π-extended core-modified figure-of-eight [38]hexaphyrins(6.1.1.6.1.1) exhibiting strong NIR absorption were synthesized to examine how pyrrole annulation controls protonation-induced topology switching and aromaticity modulation. The nonannulated system undergoes protonation-driven planarization with enhanced global aromaticity, whereas β-annulation rigidifies the macrocycle and preserves the figure-of-eight topology upon protonation. TD-DFT calculations, aromaticity descriptors, and ring-current analysis show that annulation localizes the electronic response and that the NIR Q-type bands arise mainly from local excitations rather than global aromaticity.