A Cu2+-specific colorimetric sensor 1, which is stabilized by an intramolecular hydrogen bonding, was designed and developed. The color of 1 changes from purple to blue on addition of 1.0 μM Cu2+ in aqueous buffer solution, which can be detected by the naked eye. The analytical detection limit for Cu2+ by the naked eye is as low as 1.0 μM. The stoichiometry for 1 and Cu2+ in complex is 2: 1 in aqueous solution.
