The methyl pheophorbide-a (MP-a) and methyl pyropheophorbide-a (MPP-a) were modified by reaction of exocyclic ketone in E-ring with nucleophilic reagent and several chlorin derivatives were synthesized.
The change of the structure in E-ring served an expanding conjugation region and introduction of electron-withdrawing group, which strongly influenced the visible spectra.
The Qy bands of synthesized compounds were affected by the substituents on the Qy axis (N21-N23).