A new pyridine-dicarbohydrazide-based turn-off fluorescent and colorimetric chemosensor for selective recognition of Cu 2+

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 Cu 2+ cations. P3 displayed selective fluorescence quenching and a UV-vis redshift only in the presence of Cu 2+ ions. Job’s plot, NMR titration, and ESI + -MS data were used to determine the complex’s 1:2 stoichiometry between P3 and Cu 2+ . Fluorescence titration was used to calculate the association constant (K a ) as 2.9–3.5 × 10 11 M − 2 and the limit of detection (LOD) as 4.2 × 10 − 9 M. P3-based test strips were developed, which might be used as a simple and effective Cu 2+ test kit. DFT calculations were also performed to optimize the structures of the P3 and P3 + Cu 2+ complex. This design will likely provide another avenue to develop chemosensors incorporating a functional group on the upper rim of the 2,6-pyridinedicarbohydrazide platform.