Previous research has suggested that the fluorescence of dimethylaminocyanostilbene (DCS) is selectively quenched by copper(II) ions.1 This study aimed to elucidate the fluorescence quenching mechanism and to explore its potential application to screen for copper ions in water samples. A spectroscopic Job Plot analysis was used to determine the stoichiometric ratio of DCS–copper(II) ion binding.2 Additionally, DCS was mixed with various buffered metal ion solutions and tested in different pH environments to reveal any ion-dependent and/or pH-dependent fluorescence response. Nuclear magnetic resonance spectroscopy (NMR) analysis of DCS mixed with various amounts of buffered copper(II) solution was also performed to further study the interaction between copper(II) ions and DCS.