For 10 points, name this class of nitrogenous biological pigments that includes chlorophyll and the heme complex of hemoglobin.
For some animals, it is thought that some of this class of molecules are involved in activating hormones from the pituitary gland related to the period of female sexual heat, and are also used as photosensitive receptors of light when in the skin of some mollusks and cnidarians. Their molecules are flat and contain a ring of 12 carbon and 4 nitrogen atoms, the latter of which are positioned so as to form a square in the center of the molecule, and are linked to a metal atom, forming a chelate complex.  For 10 points, name this class of nitrogenous biological pigments that includes chlorophyll and the heme complex of hemoglobin.
For some animals, it is thought that some of this class of molecules are involved in activating hormones from the pituitary gland related to the period of female sexual heat, and are also used as photosensitive receptors of light when in the skin of some mollusks and cnidarians.
Porphyrins