A new pyridine-dicarbohydrazide-based turn-off fluorescent and colorimetric chemosensor for selective recognition of Cu2+

Abstract

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. P3 displayed selective fluorescence quenching and a UV-vis redshift only in the presence of Cu²⁺ ions. Job’s plot, NMR titration, and ESI⁺-MS data were used to determine the complex’s 1:2 stoichiometry between P3 and Cu²⁺. Fluorescence titration was used to calculate the association constant (K_a) as 2.9–3.5 × 10¹¹ 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 Cu²⁺ test kit. DFT calculations were also performed to optimize the structures of the P3 and P3 + Cu²⁺ 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.