Synthesis and spectral investigation of a Turn-On fluorescence sensor with high affinity to Cu²⁺

Three anthracene derivatives (1a, 1b and 1c) containing a Schiff base moiety were synthesized and investigated as chemosensors for the detection of Cu²⁺. 1a displayed extremely high selectivity to Cu²⁺ over other 12 interference ions with 120-fold fluorescence enhancement at 468 nm in the acetonitrile media. The nitrogen atom in Schiff base and sulfur atom of 1a provided a binding scaffold for recognition of Cu²⁺ with high affinity (Ka = 4.35 × 10⁴M^-1). The formation of 1a-Cu²⁺ complex caused a decrease of electron density on nitrogen atom and sequentially led to fluorescence enhancement based on the photoinduced electron transfer (PET) mechanism. The design used for these three molecules afforded a new model for construction of fluorescence sensors based on PET mechanism.