Polychromatic Butterfly‐Shaped Thiopyrimidine‐Derived Schiff Base Probe for Sequentially Detecting Trace In ³⁺ and Fe ³⁺ and Application

A polychromatic butterfly‐shaped Schiff base probe DSP was designed and synthesized based on 2, 5‐thiophenedicarboxaldehyde and 4‐hydrazineyl‐5, 6, 7, 8‐tetrahydrobenzo [4, 5]thieno[2, 3‐d]pyrimidine. DSP could monitor In 3+ and Fe 3+ sequentially, accompanied by the “yellow–orange–light green” multicolored change under the naked eye and the “off–on–off” fluorescence performance under the UV lamp in DMF/H 2 O = 9/1. DSP showed high sensitivity and selectivity toward In 3+ and Fe 3+ in the presence of other metal ions with detection limits of 42 and 68 nM, respectively. The complex stoichiometry of DSP with target ions was determined to be 1:2 via Job's plot analysis, which was further verified by ESI‐MS titration and theoretical calculations. DSP has been validated as a promising tool for detecting In 3+ and Fe 3+ in real‐world water samples. Furthermore, a DSP test strip has been successfully developed, enabling on‐the‐spot detection of In 3+ and Fe 3+ .