Squaraine-based colorimetric and fluorescent sensors for Cu2+-specific detection and fluorescence imaging in living cells

New squaraine-based chemosensors SQ1 and SQ2 functionalized with 2-picolyl units were first synthesized and used as highly selective and sensitive colorimetric and fluorometric dual-channel sensors for Cu2+-specific recognition in aqueous systems. Among a series of individual metal ions, only Cu2+ could result in dramatic color changes. We also evaluated their capability of biological applications and found that SQ2 could be successfully employed as a Cu2+-selective probe in the fluorescence imaging of living cells.