From crystal packing to chemical sensing: substitution-guided design of naphthalimide schiff Bases for dual detection of carbonate and hydrogen sulfide.

A systematic substitution-based approach was used to probe how the molecular structure impacts crystal packing and anion-sensing in four Schiff bases derived from N-amino-1,8-naphthalimide. The derivatives, with 3-ethoxy (3E), 4-diethylamino (4D), 5-bromo (5B), and 2-hydroxynaphthyl (HN) substituents, were synthesized and characterized by NMR, FT-IR, HRMS, and single-crystal X-ray diffraction. Structural analysis discloses notable differences in molecular planarity and supramolecular organization based on substitutions, influenced by hydrogen bonding, π-π stacking, C-H···π, and halogen-bonding interactions. Photophysical studies showed different response to anions. The 5-bromo derivative (5B) showed selective dual sensing for carbonate (CO₃2-) and hydrogen sulfide (H₂S), along with colour changes and fluorescence enhancement. 5B had detection limits in the micromolar range, with a 1:1 binding ratio. These findings establish a clear connection between structure, packing and function. Also provide a thoughtful strategy for designing multifunctional Naphthalimide based fluorescent chemosensors aimed at important environmental and biological analytes.