pyr·ro·porphyrin \|pi(ˌ)rō+\noun Etymology: International Scientific Vocabulary pyrrh- + porphyrin : a dark red crystalline pigment C32H36N4O2 with a violet metallic luster that is the lower homologue of phylloporphyrin and that differs from most porphyrins in being a hepta-substituted derivative of porphin rather than an octa-substituted one