Furan-modified fluorene functionalized chitosan fluorescent hydrogel: preparation and fluorescent sensing toward Fe3+ and Hg2+

The novel furan-modified fluorene-based fluorescent small molecules were synthesized. • A catalyst-free Diels–Alder cycloaddition is utilized to crosslink chitosan, affording a mild fabrication strategy. • The as-prepared fluorescent hydrogel exhibits fluorescence color change behavior under ultraviolet light irradiation. • The fluorescent hydrogel achieve dual detection of Fe 3+ and Hg 2+ in aqueous solutions. In this study, a fluorescent furan-modified fluorene molecule ( F-Fu ) was first synthesized via a Stille coupling reaction. Using F-Fu as a cross-linker, a novel chitosan-based fluorescent hydrogel was successfully prepared through a Diels-Alder reaction between furan-functionalized F-Fu and maleimide-modified chitosan derivatives. The SEM results revealed the hydrogel has a porous network structure with pore sizes ranging from 60 to 100 μm. Rheological characterizations reveal dominant elastic responses (G′>G″), and the elastic modulus is elevated upon increasing crosslinking density. The hydrogel emits blue-violet fluorescence. The main emission peak at 385-386 nm originates from the π-π* transition of the fluorene core, and the shoulder peak at 398-402 nm is attributed to intramolecular charge transfer (ICT). Upon ultraviolet irradiation, the hydrogel exhibits green fluorescence, with its emission peaks merging and undergoing a blue shift to 378-382 nm. In aqueous dispersion, the fluorescence is readily quenched by Fe 3+ and Hg 2+ ions, enabling their sensitive detection. Owing to the paramagnetic or heavy-atom effect upon coordination, the LOD values for Fe 3+ and Hg 2+ are 0.064 ppm and 0.199 ppm, respectively. Download: Download high-res image (304KB) Download: Download full-size image