Porphyrin
= Porphyrin
A <porphyrin> has a large conjugated ring system built from four nitrogen-containing pyrrole-derived units linked through carbon bridges. Its inner nitrogen atoms can coordinate a metal ion.
An iron-containing porphyrin forms part of <haem>, while related macrocyclic chemistry occurs in other biological pigments. The conjugated framework supports strong optical absorption, connecting visible color with electronic structure and metal coordination.