Design and synthesis of AIE-active naphthaldehyde hydrazone-based ligand: Mechanochromic, acidochromic, and sensing studies

Abstract

A new multifunctional Schiff base material, 1-((E)-(((Z)-3,5-difluoro-2hydroxybenzylidene)hydrazineylidene)methyl)naphthalen-2-ol (L2), was synthesized through a simple one-step condensation of 2-hydroxy-1-naphthaldehyde hydrazone and 3,5difluorosalicylaldehyde. The ligand was characterized by FT-IR, 1 H and 13 CNMR, ESI-MS and single crystal X-ray diffraction. The crystal structure of L2 crystallizes in the monoclinic system with the space group P 1 2₁/c 1 . The compound exhibited aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics, along with reversible mechanochromic and acidochromic behavior. L2 functioned as a rapid, sensitive, and reversible colorimetric as well as fluorometric "turn-off" response for Cu²⁺ ions in aqueous media, displaying a 1:1 binding stoichiometry and an exceptionally low detection limit of 0.71 μM. The sensor L2 was effectively applied for Cu 2+ detection in on-site detection kit.Moreover, bioimaging studies demonstrated its excellent cell permeability, low cytotoxicity, and efficient Cu 2+ sensing within living cells.