Fig. 1: Chemical structures of porphyrin, porphyrin analogs, and their dimers.

a Porphyrin and related monomeric macrocycles; b examples of “Planar–Twisted–Planar” dimers: the two planar porphyrin/porphyrinoid units are linked in a highly twisted manner; c examples of “Planar-Planar-Planar” dimers: the two planar porphyrin units are linked by means of direct fusion; d “Twisted–Planar–Twisted” dimer D reported in this work: Note that the twisted hexaphyrin units are linked through a coplanar bipyrrolic linkage. Ar represents aromatic substituents. The blue-colored pyrrolic units represent confused pyrroles, which are linked with adjacent pyrroles or meso-carbons through Cα-Cβ or N-Cβ atoms.