Phosphorescent compounds, chemical structures

Fig. 3 Chemical structures of some fluorescent and phosphorescent compounds.

For a complete picture, we should briefly refer to the influence of the chemical structure of the emitting molecule. As with fluorescence, aromatic compounds are most important because they may yield phosphorescence. A shift of this emission toward longer wavelengths with an increase in the number of condensed benzene rings is observed. Introduction of a heteroatom into the aromatic electron system (e.g., in a polyaromatic hydrocarbon) or substitution by atoms of high atomic number (e.g., the internal heavy-atom effect of bromine or iodine) usually... 

It should be stressed, finally, that phosphorescence of an analyte, or its derivatized compound, is a rather complex process that can be affected drastically by slight modifications of the chemical structure or small variations of the chemical nature of the environment. 

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