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 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.