Selective fluorescence quenching of nitrogen-containing polycyclic aromatic hydrocarbons by aliphatic amines

In this investigation, primary, secondary, and tertiary amines are evaluated for their efficiency and selectivity as fluorescence quenchers for polycyclic aromatic hydrocarbons (PAHs) and nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs). In general, the quenching efficiency tends to increase from primary to tertiary amine due to a greater number of alkyl groups that increase the electron-donating ability. However, the selectivity decreases from primary to tertiary amine. The effect of low concentrations of water is also examined. Because water can form hydrogen bonds with amines, the nonbonding electron pair is not available for interaction with the fluorophore, thus the quenching constant is decreased. These aliphatic amines are then applied to PAHs and N-PAHs and some interesting trends are observed. Whereas amino-PAHs remain virtually unquenched by different amines, aza-PAHs are all quenched well. The selectivity between aza-PAHs and amino-PAHs is as high as several hundred. This trend provides an easy and effective method to discriminate between these classes of N-PAHs. Moreover, the alternant aza-PAHs are quenched more than their corresponding alternant PAHs