Fluorescence Sensor with A New ON 1 –OFF–ON 2 Switching Mechanism Using the Excited State Intermolecular Proton Transfer Reaction of An Anthracene‐diurea Compound

A new photoreaction mechanism of “Three‐state molecular switch” fluorescence sensor based on ON 1 ‐ OFF ‐ ON 2 sequence was achieved by anthracene‐diurea compound, which was designed using two phenylurea groups and one anthracene, 9,10Bt DSPUA . Photochemical properties of 9,10Bt DSPUA and interaction between 9,10Bt DSPUA and anion were investigated in detail by absorption, 1 H NMR , fluorescence, and fluorescence decay measurements. While the fluorescence of 9,10Bt DSPUA in DMSO ( ON 1 ) was quenched in the presence of low concentration of acetate anion ( OFF ), fluorescence enhancement occurred by the addition of high concentration of acetate anion ( ON 2 ). This compound forms complex with acetate anion through hydrogen bonding interaction in the ground state resulted in tautomer formation by excited state intermolecular proton transfer ( ESIPT ) on irradiation. Whereas single coordination of acetate anion to anthracene‐diurea compound may cause fluorescence quenching, full coordination may cause fluorescence enhancement due to suppressing ESIPT . This suppressing ESIPT was occurred by electron‐donating resonance effect between two urea moieties. This study is the first example of ON 1 ‐ OFF ‐ ON 2 fluorescence sensor for concentration detection of acetate anion.