Chlorin derivatives (Ia) and (Ib), are new. Chlorin derivative of formula (Ia) or (Ib) are new. R10 : OH, alkoxy, monoalkylamino and dialkylamino; and M : 2H or metal, provided that when M is H, then each hydrogen is linked to nitrogen of the chlorin derivative. N.B.: Structures (Ia) and (Ib) are not present in the patent specification.