A new indole-containing 2,6-pyridinedicarbohydrazide P3 was synthesized and well characterized employing NMR, ESI⁺-MS, FT-IR, and elemental analyses. The synthesized compound was examined as an efficient fluorescent turn-off and colorimetric cation receptor. The P3 receptor exhibited a remarkable rapid color change from colorless to brown in the presence of Cu²⁺ cations.
