<p>It is significant to develop a simple, rapid and low-cost analytical method for selective detection of Cu²⁺ ion. In this paper a new coumarin-based fluorescent probe CL was designed and synthesized for detection of Cu²⁺ ion. The probe not only showed a large Stokes shift of 218&#xa0;nm, but also displayed fluorescence emission in near-infrared (NIR) window. Addition of Cu²⁺ ion to aqueous solution of probe CL caused quenching of fluorescence emission at 653&#xa0;nm, and color change from red to yellow. Probe CL exhibited excellent selectivity towards Cu²⁺ and good anti-interference performance over other common competitive metal ions including Li⁺, Na⁺, K⁺, Ag⁺, Fe²⁺, Hg²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺, Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺ and Fe³⁺. Probe CL could be used for sensing Cu²⁺ over a wide range of pH 5–11, with the detection limit of 2.31 µM. Sensing of Cu²⁺ based on photo-induced electron transfer (PET) mechanism by probe CL was revealed by spectral test and density functional theory (DFT) calculation.</p>