A fluorescent and colorimetric chemosensor for Ga3+ and CN–

•A simple Schiff-base chemosensor 1 for Ga3+ and CN– was designed and synthesized.•Sensor 1 exhibited “turn-on” fluorescence response only to Ga3+, distinguishing from Al3+ and In3+.•Sensor 1 detected CN– by color change from yellow to colorless through a nucleophilic addition mechanism.•Sensing mechanisms of 1 toward Ga3+ and CN– were explained by the various spectroscopic studies and theoretical calculations.