The success exhibited by Photofrin and the potential shown by a number of the second-generation photosensitizers has caused an explosion in photodynamic therapy, resulting in the unveiling of new photosensitizers along with an investigation into well-known naturally occurring chromophores.

Hypericin, for example, is welldocumented as having photodynamic activity as it causes hypericism or photopoisoning in grazing animals that consume large quantities of plants containing this compound, often leading to skin irritation, fever and even death[98]. This multicyclic quinione, which absorbs light at around 590 nm[96], is being investigated as a photosensitizer for PDT and is presently in Phase I clinical trials for the treatment of psoriasis, warts and skin cancer.
The naturally occurring perylenequinones such as hypocrellins, which are produced by fungi and insects, are also under evaluation as PDTs. Several pharmaceutical companies are actively developing new synthetic photosensitizers.

For example, Scotia Pharmaceuticals is interested in bacteriochlorins for photodynamic therapy while Hamamatsu Phototonics is investigating ATXS10, a chlorin derivative.
In reality, any chromophore that can effectively produce photocytotoxicity upon illumination has the potential to be used in photodynamic therapy, leading to endless possibilities.