Novel Flavonoid Photoswitchable "Turn-On" Fluorescent Chemosensors: Synthesis of Bromo Flavonols for Nanomolar Aluminum Ion Detection and Cellular Imaging, among Other Applications.

Aluminum (Al), a non-essential element in living systems, can potentially cause chronic toxicity. Therefore, it is crucial to have a specific and sensitive method for detecting Al in order to assess its risk to life. In this study, we designed and synthesized a novel fluorescent probe (IV) based on bromoflavonol. Upon binding to Al, probe IV exhibits a blue shift in emission and enhanced fluorescence, making it suitable for Al detection. Our UV-Vis absorption and fluorescence emission spectra demonstrate that probe IV has high selectivity and sensitivity towards Al while being immune to interference from other metal ions. Through fluorescence titration, we determined that the detection limit (LOD) of probe IV for Al is 1.8 × 10 mol/L. Job's curve and  H NMR titration further confirmed a 1:1 binding stoichiometry between probe IV and Al. Additionally, using DFT (Density Functional Theory), we calculated the energy gap difference between IV and IV + Al and found that the complex formed by probe IV and Al is more stable than IV alone. We successfully detected Al in tap water and river water from the middle regions of the Han River, achieving recoveries of over 96% using this probe. This demonstrates its potential for quantitative detection of Al in environmental water samples. Moreover, we successfully used the probe for imaging Al in MG63 cells, suggesting its potential application in biological imaging.