Hydrogen bond induced fluorescence recovery of coumarin-based sensor system

Two coumarin-type fluorescent sensors were synthesized and their fluorescence response to pH value was investigated. The fluorescence intensity of sensor 3 and sensor 4 is obviously enhanced along with the increase of pH from 7 to 12 and the reduction of pH value from 8 to 1, respectively. Possible mechanism for these fluorescence recovery systems is proposed. Intramolecular hydrogen bond could be formed under different condition, which blocks electron transferring route from nitrogen atom to fluorophore. The blue fluorescence color change of the two sensory systems could be directly detected by naked eyes under UV-lamp for pH values.