B ← N coordination bond reinforced dynamic fluorescence of pH-responsive amphiphile alginate aggregates for anti-counterfeiting

High quantum yield polysaccharide-based materials are significative for the dynamic anti-counterfeiting, while that are limited by weak fluorescence. However, natural polysaccharides with weak fluorescence are not suitable for anti-counterfeiting. Herein, alginate derivatives (SA-PBA) exhibiting aggregation-induced emission with high-quantum yields were synthesized by grafting phenylboronic acid (PBA) onto a sodium alginate (SA) chain. As the concentration increases, polymer assembly can be induced to form more compact soft colloidal aggregates, which enhances the fluorescence properties of alginate derivatives by introducing B ← N coordination bonds in the hydrophobic microregions. Interestingly, the clustered aggregates of SA-PBA can be dynamically controlled by pH, realizing the reversible adjustment of fluorescence. The corresponding mechanism is revealed by the combination of coarse-grained simulations and experiments. It is found that SA-PBA uses a hydrophobic driving force and hydrogen bond interaction to self-assemble in an aqueous solution and promote fluorescence emission. Moreover, the fluorescence quantum yield of SA-PBA can reach 14.4 % and can be reversibly altered by tuning soft colloidal microstructures. Therefore, a reversible information encryption system of SA-PBA is developed for anti-counterfeiting. This work shed some light on how to design novel anti-counterfeit materials based on natural polysaccharides and optimize the dynamic fluorescence conditions.