The photophysics of photosensitization: A brief overview

The concept of photosensitization had its origins in the serendipitous discovery in the 19th century that dye molecules could enhance the spectral range of photographic emulsions. In the latter half of the 20th century, photosensitization reached maturity as a mechanistic photochemical tool for the identification and quantification of the role of triplet states as intermediates in organic photoreactions in solution. The photophysical properties desirable in a photosensitizer and the kinetic aspects of the diffusional encounter of sensitizer and energy acceptor are outlined, together with the role of spin selection rules in photosensitization processes, with emphasis on the photosensitized formation of singlet oxygen, the key photophysical step in Type II photosensitization.