Abstract: Dimers which are either esters or amides of (1) a purpurin, a chlorin or a metal complex and (2) hematoporphyrin or a purpurin, a chlorin or a metal complex are disclosed. The purpines and their metal complexes have the structures of FIGS. 1, 7, 14-18, 29-38, 44-48 and 54-58 of the attached drawings. The chlorins and their metal complexes have the formulas of FIGS. 2, 8, 19-28, 39-43 or 49-53 of the attached drawings. Solutions of the purpurins, chlorins and metal complexes which are physiologically acceptable for intravenous administration are also disclosed, as are emulsions or suspensions of the solutions. The solvent for the solutions can be a product of the reaction of ethylene oxide with castor oil. A method for detecting and treating tumors in human and animal patients is also disclosed. The method comprises administering one of the dimers to the patient.