A Selective, Sensitive, Colorimetric, and Fluorescence Probe for Relay Recognition of Fluoride and Cu(II) Ions with Off-On-Off Switching in Ethanol Water Solution

Anion to cation relay recognition was designed and realized for the first time with sequence specificity (F--> Cu2+) via a fluorescence off-on-off mechanism. Probe 1 was a highly selective, sensitive, and turn-on chemodosimeter for F- through a specific cyclization reaction triggered by the strong affinity of fluoride toward silicon with a significant OFF change of fluorescence color in both ethanol and ethanol- water (1:1, v/v) solution. Fluorescence enhancement factors were dramatic: 833-fold in ethanol and 164-fold in ethanol-water (1:1, v/v) solution, respectively. The in situ system generated from the sensing of F- showed good relay recognition ability for Cu2+ via fast fluorescence quenching by the formation of a 1:1 complex in ethanol water (1:1, v/v) solution. The isolated pure compound 2 also exhibited high selectivity toward Cu2+. in PBS buffer (pH = 7.0) solution. The origin of this sequence specificity of fluorescence recognition was disclosed through the crystal or optimized structures and DFT calculations of corresponding compounds.