A simple colorimetric and fluorescent chemosensor MP was designed and synthesized and its selective signaling behaviors toward Cu²⁺ were investigated. Under the optimized conditions, the sensor exhibited specific absorbance-on and fluorescence-on responses to Cu²⁺ only, which can be tuned for detection with the naked eye. These remarkable properties may allow Cu²⁺ to be detected directly in the presence of the other examined metal ions. The limit of detection for Cu²⁺ was up to 0.096 μM. As a fluorescence turn-on sensor, cell experiments showed MP can permeate through cell membranes and react to Cu²⁺ within living cells.