A group of hydro-dibenzoporphyrins prepared by di-Diels-Alder additions at the A and C rings of the appropriate divinyl porphyrins have absorption maxima in the range of 700-820 nanometers and are photosensitizing agents. These compounds are useful in treating disorders or conditions which are subject to hematoporphyrin derivative (HPD) treatment in the presence of light, or in treating biological materials generally to destroy unwanted targets such as viruses, cells and tissues. The use of the compounds of the invention permits irradiation with wavelengths other than those absorbed by blood. The compounds of the invention may also be conjugated to ligands specific for receptors or to specific immunoglobulins or fragments thereof to home to target tissues or cells for the radiation treatment. Use of these materials permits lower levels of photosensitizer to be used, thus preventing side reactions which might destroy normal tissues.