| Abstract
| - Phenyl-1H-anthra[1,2-d]imidazole-6,11-dione (1) and its derivatives (2 and 3) have been investigatedas new colorimetric and ratiometric fluorescent chemosensors for fluoride. Acute spectral responsesof 1 and 3 to fluoride in acetonitrile have been observed: an approximately 100 nm red shift inabsorption and fluorescence emission and a very large ratiometric fluorescent response (Rmax/Rminis 88 for sensor 1 and 548 for sensor 3). From the changes in the absorption, fluorescence, and 1HNMR titration spectra, proton-transfer mechanisms have been deduced. In ground states, a two-step process has been observed: first, the formation of the sensor-fluoride hydrogen-bond complex[LH···F]- and then the fluoride-induced deprotonation of the complex to form L- and FHF-. Inexcited states, the excited-state intermolecular proton-transfer made a contribution to thedeprotonation. The selectivity for F- can be tuned by electron push−pull properties of thesubstituents on the phenyl para position of the sensors. Sensor 1 shows the best selectivity. Theexcellent selectivity of 1 for F- is attributed to the fitness in the acidity of its NH-group, which istuned to be able to distinguish the subtle difference in the affinity of F-, CH3CO2-, and H2PO4- toproton.
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