Other Infrared Fluorophores

The phthalocyanines, naphthalocyanines, and certain of their metal derivatives (Figure 6.17) are infrared fluorophores. 61"64 As a class, they are exceptionally stable compounds, with copper (Cu) phthalocyanine (not a fluorophore) remaining intact above 300 °C in air. First used for textile dyeing in the last century and still widely used, there is a rich chemistry of phthalocyanines. Most derivatives can be made by prolonged heating of a phthalimide or phthalic acid derivative with a metal in powder or salt form at elevated temperature. Several derivatives absorb in the near-IR, and either fluoresce or phosphoresce. The electronic transitions of phthalocyanines are complex and have been extensively studied, at least in part because the symmetry of the molecule makes theoretical calculations of its spectroscopic behavior more tractable. Unsubstituted phthalocyanines and naphthalocyanines are, as a class, very insoluble in solvents other than, for instance, nitrobenzene. Sulfonated phthalocyanines are water soluble and exhibit spectra comparable to the parent derivative. Photolumines-cent phthalocyanines (Pcs) include SiPc, ZnPc, and PC itself. These compounds have been little used for practical infrared fluorometry to date however, Diatron Corpora-... 

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