A novel bromination of porphyrins is described in which a compound of the chlorin class is produced. Evidence is presented in support of structure (VIa) for this compound. Mesochlorin and deuterochlorin have been prepared as model compounds during this investigation, and it has been shown by N.M.R. spectroscopy that both these chlorins have been reduced in either rings A or B and not in ring D as occurs in the chlorophylls a and b.