A new coumarin-derived fluorescent probe (1) exhibited significant fluorescence quenching in the presence of Cu2+ ions. Other metal ions, e.g. Ag+, Ca2+, Cd2+, Co2+, Fe2+, Fe3+, Hg2+, K+, Mg 2+, Mn2+, Ni2+, Pb2+, and Zn 2+, produced only minor changes in the fluorescence of chemosensor 1. The binding ratio of the chemosensor-Cu2+ complexes was found to be 2 : 1, according to Job plot experiments. The association constant (K a) for Cu2+ binding with chemosensor 1 was found to be 9.56 × 109 M-2. The maximum fluorescence quenching caused by Cu2+ binding with chemosensor 1 occurred over a pH range of 5-9. Moreover, fluorescence microscopy experiments showed that chemosensor 1 could be used as a fluorescent probe for detecting Cu2+ in living cells.