A new pyrene-based chemosensor (1) exhibits excellent selectivity for Fe(3+) ions over a wide range of tested metal ions Ag(+), Ca(2+), Cd(2+), Co(2+), Cu(2+), Fe(2+), Hg(2+), K(+), Mg(2+), Mn(2+), Ni(2+), Pb(2+), and Zn(2+). The binding of Fe(3+) to chemosensor 1 produces an emission band at 507 nm due to the formation of a Py-Py* excimer that is induced by Fe(3+)-binding. The binding ratio of 1-Fe(3+) was determined to be 1:1 from a Job plot. The association constant of 1-Fe(3+) complexes was found to be 1.27 × 10(4) M(-1) from a Benesi-Hildebrand plot. In addition, fluorescence microscopy experiments show that 1 can be used as a fluorescent probe for detecting Fe(3+) in living cells.