A cyclic indole tetramer has been synthesized via an iridium-catalysed C-H borylation-cross coupling sequence. The tetraindole has a highly distorted structure, but can be oxidized with bromine and water into a highly planar macrocycle. The oxidized macrocycle can capture metal ions in its inner cavity as a novel porphyrin analogue, accompanied by a significant colour change from purple to blue or black.