Reversible NIR fluorescent probes for Cu^sup 2+^ ions detection and its living cell imaging

A new, easily accessible “off-on-off” colorimetric and fluorescent probes are designed and synthesized. It displayed highly selective and sensitive detection towards Cu2+ ion without having any interference from other competitive metal ions. The examined UV–vis and fluorescence spectral changes are caused by the operation if the ligand to metal charge transfer (LMCT) and chelation enhanced fluorescence effect (CHEF) in the presence of Cu2+ to the present probes. Besides, the density functional theory (DFT) calculations have been theoretically supported the photophysical changes. These probes are potentially applied in an analytical application for detecting the trace amount of Cu2+ ions in real water samples. Furthermore, these probes are successfully applied for fluorescence imaging of Cu2+ in HeLa cells. Finally, the use of test strips based on these probes is fabricated, which could act as a convenient and efficient Cu2+ test kit in solution medium and supported on solid medium (silica).