Rational design of aggregation-induced emission sensor based on Rhodamine B for turn-on sensing of trivalent metal cations, reversible data protection, and bioimaging

A novel AIE-active molecule (TPEThRB) composed of a tetraphenylethene unit, Rhodamine spirolactam, as a receptor, and thiophene ring as a conjugated electron-rich linker was obtained. It can be utilized to effectively detect trivalent metal cations and H⁺ ions, accompanied with visible color change and turn-on fluorescence enhancement. The four species can be further recognized individually through UV-Vis analysis. Moreover, compared to the conventional manner of metal ion chelation-induced ring-opening form of Rhodamine B derivative, the interaction of TPEThRB with trivalent cations is ascribed to the synergy of proton-induced open-cycle and the subsequent coordination interaction due to the steric effect and acidic hydrolysis of trivalent metal cations. In addition, in view of its acidochromism property with reversible color and fluorescence changes, AIE-active TPEThRB may be a prominent smart material for data protection by employing trifluoroacetic acid vapor as the chromogenic reagent and diethylamine vapor as the eraser. Owing to the AIE characteristics and the remarkable photophysical response characteristics towards trivalent metal ions in vitro, TPEThRB is suitable for fluorescence ratio imaging of trivalent metal cations in living cells.