Single-Acetylene Linked Porphyrin Nanorings

The synthesis of ethyne-linked porphyrin nanorings has been achieved by template-directed Sonogashira coupling. The cyclic hexamer and octamer are predicted by density functional theory to adopt low symmetry conformations, due to dihedral twists between neighboring porphyrin units, but their symmetries are effectively <i>D</i>_6h and <i>D</i>_8h, respectively, in solution by ¹H NMR. The fluorescence spectra indicate that the singlet excited states of these nanorings are highly delocalized