Dansyl Hydrazine Modified Cellulose as a Fluorescent Schiff Base for Selective Dual Sensing of 4-Nitroaniline and Cu(II) Ions

Abstract

A sustainable and multifunctional fluorescent sensor based on a dansyl hydrazine-derived cellulose-modified Schiff base (DHCSB) was successfully designed and synthesized for the dual detection of 4-nitroaniline (4-NA) and Cu(II) ions in solution. Dialdehyde cellulose was first prepared and subsequently functionalized through Schiff base condensation with dansyl hydrazine, forming a fluorescent material exhibiting strong green emission centered at 490 nm. The sensor demonstrated pronounced fluorescence quenching upon the addition of 4-nitroaniline and Cu(II), enabling sensitive detection of both analytes. Stern−Volmer analysis revealed efficient quenching behavior, indicating strong interaction between the DHCSB and the analytes. The quenching mechanism toward 4-nitroaniline is attributed to photoinduced electron transfer (PET) and possible π−π interactions between the electron-rich dansyl moiety and the electron-deficient nitroaromatic compound. In contrast, Cu(II) sensing arises from coordination between the metal ion and the imine/hydrazine donor sites of the Schiff base, resulting in chelation-enhanced quenching (CHEQ) and paramagnetic-induced non-radiative decay. The fluorescence quenching mechanism was elucidated using a combination of optical characterization and density functional theory (DFT) calculations. The integration of a renewable cellulose backbone with a conjugated dansyl fluorophore provides structural stability, multiple coordination sites, and enhanced sensing performance. This work presents a versatile cellulose-based fluorescent platform for environmentally relevant analytes and contributes mechanistic insight into dual-mode quenching involving organic electron acceptors and transition metal ions.