Phthalocyanines are a class of dyes discovered in 1907. They were fully characterized by the end of World War I through techniques like elemental analysis and oxidative degradation. X-ray crystallography in 1930 proved their core structure. Any transition metal can be placed at their center. Phthalocyanines absorb around 620-700nm but aggregate in solutions, reducing their photophysical properties. Substituted phthalocyanines, like fluorinated versions, have improved stability and can be used as catalysts, photosensitizers, and probes for imaging applications.