Selective fluorescence quenching of polycyclic aromatic hydrocarbons by aliphatic amines

The ability of primary, secondary, and tertiary mono- and diamines to serve as fluorescence quenchers for polycyclic aromatic hydrocarbons (PAHs) has been evaluated in acetonitrile and methanol, In general, the efficiency of quenching increases with the electron-donating ability of the amine and with the number of amine groups. The selectivity for nonalternant PAHs relative to the alternant isomers appears to decrease as the quenching efficiency increases. Nevertheless, all of the amines exhibit greater selectivity than 1,2,4-trimethozoibenzene, a previously characterized selective quencher for nonalternant PAHs, The experimentally measured rate constants for dynamic quenching show good agreement to those predicted by Rehm-Weller electron-transfer theory in the solvent acetonitrile, In contrast, the rate constants in methanol are anomalously low and do not conform well to Rehm-Weller theory. Presumably this is due to explicit hydrogen bonding between the solvent and quencher, which decreases the concentration of the free amine that is available for fluorescence quenching.