Chromene-chromene Schiff base as a fluorescent chemosensor for Th⁴⁺ and its application in bioimaging of Caenorhabditis elegans

The manuscript presents the synthesis of a new di-chromene Schiff base (COM-CH) by combining 7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide and 4-oxo-4H-chromene-3-carbaldehyde, and its characterization using various analytical techniques. The probe COM-CH functional group contains a hard donor atom that selectively complexes with Th⁴⁺ ions. This report investigated COM-CH's sensing ability towards Th⁴⁺ chromogenic and fluorogenic methods in ACN: H₂O (8:2, v/v) with Th⁴⁺ ions. The COM-CH-Th⁴⁺ complex was excited at 430 nm, resulting in a bright emission band at 475 nm with a 45 nm Stokes shift. The COM-CH probe demonstrated the highest performance at pH 4.0 to 8.0, with a sensitivity of 18.7 nM. The complex formation of COM-CH with Th⁴⁺ was investigated using NMR, FTIR spectrometry, and density functional theory calculations. The COM-CH and Th⁴⁺ are bound with 2:1 stoichiometry and an association constant of 1.92 × 10⁸ M^-2. The probe's performance enabled the analysis of monazite sand and water samples for Th⁴⁺ content. The probe successfully detected Th⁴⁺ content in Caenorhabditis elegans, marking the first Th⁴⁺ detection in animal models.