Controllable fabrication of stimuli-responsive fluorescent silica nanoparticles using a tetraphenylethene-functionalized carboxylate gemini surfactant

Exploring stimuli-responsive luminescent materials is still an urgent need for fabricating smart nanodevices. Herein, by taking advantage of the aggregation-induced emission (AIE) effect originating from nonconventional chromophores, stimuli-responsive fluorescent silica nanoparticles (SiO2-NH2-F) have been facilely constructed without adding any fluorophores. The SiO2-NH2-F can not only provide fascinating blue emission but also contrasting fluorescence and shape-transforming responses to acidic pH and high temperature. Significantly, the nanostructure and stimuli-responsive fluorescence properties of SiO2-NH2-F could be further tuned using a tetraphenylethene (TPE)-functionalized carboxylate gemini surfactant (N-16-TPE-N-16). Owing to its unique chemical-structure, surface-activity, pH-sensitivity and fluorescent properties, the designed N-16-TPE-N-16 can not only serve as an ingenious "additive" to regulate the construction of SiO2-NH2-F in the structure-directing process but also provide anchored fluorophores and chromophores to improve its original photoluminescence. By appropriately tuning the concentration of N-16-TPE-N-16, shape-controlled fluorescent silica nanoparticles (AIE-SNs-F) can be prepared directly, producing three different types of silica nanorods (AIE-300-F, AIE-400-F and AIE-600-F). In particular, the incorporated N-16-TPE-N-16 will further endow the AIE-SNs-F with enhanced fluorescence intensity, especially for longer wavelength bands (up to 3.7-fold), accompanied by improved sensitivity to acidic pH and temperature. The developed AIE-SNs-F integrates two kinds of AIE characteristics into a single system, opening up a new avenue for the controllable fabrication of multifunctional fluorescent nanomaterials.