Merocyanine dye 1 was prepared as an effective colorimetric and fluorescent chemosensor for copper ions in aqueous media, and displays a significant color change from reddish-purple to yellow with a large blue shift of 94 nm in its absorption spectrum in the presence of one equivalent of copper. As an on–off fluorescent sensor, it is feasible to detect copper ions in living cells due to its good cell permeability and high solubility under physiological conditions.