Photosensitizers are compounds that are capable of absorbing light of a specific wavelength and transforming it into useful energy. In the case of PDT, this would involve the production of lethal cytotoxic agents. There are hundreds of natural and synthetic dyes that can function as photosensitizers for PDT, ranging from plant abstracts to complex synthetic macrocycles.

The ideal photosensitizer:
  • should be chemically pure and of known specific composition,
  • should have a high quantum yield for singlet oxygen production,
  • should have a strong absorption with high extinction coefficient e at longer wavelength (red) region preferably between 700-800nm,
  • should have an excellent photochemical reactivity,
  • should possess minimal dark toxicity,
  • only be toxic in the presence of light,
  • should have preferable retention by target tissue (tumour cells),
  • should be rapidly excreted from the body,
  • should be synthesisable from easy available precursors.

The most famous photosensitizer are: