Ratiometric Fluorescence Sensors for 1,2-Diamines Based on Trifluoromethyl Ketones

Two BINOL-based trifluoromethyl aryl ketones 3 and 4 show greatly enhanced fluorescence at 375 nm accompanied by a decrease at 500 nm when treated with aliphatic 1,2-diamines, especially ethylenediamine, in organic solvents. Under the same conditions, other monoamines and diamines caused much smaller or no fluorescence response. Thus, both 3 and 4 can be used as highly selective ratiometric fluorescence sensors for ethylenediamine. Compound 3, the BINOL hydroxyl groups of which are protected, exhibits greater fluorescence enhancement than the corresponding unprotected compound 4. UV and NMR spectroscopic studies have been conducted to probe the mechanism of the sensor–substrate reaction.