Atropisomerism is a frequently overlooked source of structural diversity in drug development. Photosensitizer development for photodynamic therapy (PDT) is not an exception. The present work aimed at investigating the efficacy of redaporfin (and precursor porphyrin) atropisomers for use in PDT. Redaporfin is a synthetic sulphonamide fluorinated bacteriochlorin with enhanced photostability, strong absorption at 750 nm and high ROS yields which is currently in clinical trials for head and neck cancer (NCT02070432). This bacteriochlorin and related porphyrin have phenyl-macrocyclic single bonds with hindered rotations that can generate a different spatial distribution of the sulphonamide groups in the meta positions. The present work demonstrated that it is possible to separate the four atropisomers of redaporfin, and related porphyrins and chlorins. They are designated as: α4 when all the sulphonamides of the phenyl groups are on the same side of the macrocycle plane; α3β when three of the sulphonamides are in the same side of the plane and one is on the other side of the plane; α2β2 when two sulphonamide groups are on each side and adjacent to each other and finally, αβαβ when two sulphonamides are on each side but alternate in the positions with respect to the macrocycle. Although the photo and physicochemical properties of the four atropisomers are similar, their therapeutic efficacies are dramatically different: the α4 atropisomer is orders of magnitude more toxic than the less photoactive αβαβ atropoisomer. Similar results were found for bacteriochlorins and porphyrins.