Fluorescent moieties emit photons several nanoseconds after absorption following an exponential decay curve, which differs between dyes and depends on the surrounding solvent. When the dye is attached to a macromolecules the decay curve becomes multiexponential. Conjugated dyes generally have a lifetime between 1–10 ns, a small amount of longer lived exceptions exist, notably pyrene with a lifetime of 400ns in degassed solvents or 100ns in lipids and coronene with 200ns. On a different category of fluorphores are the fluorescent organometals (lanthanides and transition metal-ligand complexes) which have been previously described, which have much longer lifetimes due to the restricted states: lanthanides have lifetimes of 0.5 to 3 ms, while transition metal-ligand complexes have lifetimes of 10 ns to 10 µs. Note that fluorescent lifetime should not be confused with the photodestruction lifetime or the "shelf-life" of a dye.