A dual responsive novel bipyridyl carbohydrazide Schiff base as a colorimetric-fluorescent probe for In3+ and Al3+ ions and its potential applications

Abstract

The development of a probe for the selective recognition of trivalent cations Al³⁺ and In³⁺ has recently received greater attention due to the crucial roles these metal ions play in many biotic and material processes. In this regard, [2,2′-bipyridine] 6,6′-dicarbohydrazide has been designed to synthesize a Schiff-base (L) using diethyl amino salicylaldehyde for the selective detection of Al³⁺ and In³⁺. The probe L exhibits selective colorimetric response at 444 nm with In³⁺ and turn-on fluorescence response at 497 nm with Al³⁺ in DMSO : H₂O (7 : 3, pH = 7.4). The probe L could form a 1 : 2 [L : M] stoichiometry complex confirmed by Job's plot and ESI mass analysis with an estimated association constant of 9.38 × 10³ M⁻² and 4.75 × 10⁴ M⁻² with Al³⁺ and In³⁺ ions, respectively. The probe could detect Al³⁺ and In³⁺ down to 10.98 nM and 110 nM without much interference from other common interfering ions. Inhibition of CN isomerization and chelation-enhanced fluorescence (CHEF) could be induced to vary the photophysical properties of L upon interaction with Al³⁺, whereas, the L with In³⁺, exhibits ligand-to-metal charge transfer (LMCT) due to the presence of vacant f-orbitals. The binding mechanism of probe L with metal ions was investigated using ¹H NMR, mass, and DFT studies. More importantly, the potential application of probe L could be used to quantify Al³⁺ and In³⁺ in water samples and Al³⁺ in DrG cells and a zebrafish in vivo imaging model.