There has been considerable interest in the development of photosensitizers having increased
absorption in the red or near infrared region for PDT applications. It is known that porphyrin
absorptions can be shifted to longer wavelengths by expanding the n-conjugation of the macrocycle
and by introducing electron-withdrawing groups at the ring. This principle has been applied to a
number of porphyrinone (oxochlorin), porphyrintriones (dioxobacteriochlorins and dioxoisobacteriochlorins),
as well as a porphyrintrione. The oxo group in this class of compounds has been
transformed into sulfido-, imino, and methide derivatives, i.e., the ring system contains at least one
exocyclic double bond connected to S, N-CN, and C(CN)2 using suitable reaction conditions. Many of
these compounds exhibit absorption maxima longer than 700 nm, some even in the 800 nm region.
Since the porphyrinones are generally photodynamically active to in vitro cells, they are attractive
for PDT drug use.