Red-Shift (2-Hydroxyphenyl)-Benzothiazole Emission by Mimicking the Excited-State Intramolecular Proton Transfer Effect

Novel strategies to optimize the photophysical properties of organic fluorophores are of great significance to the design of imaging probes to interrogate biology. While the 2-(2-hydroxyphenyl)-benzothiazole (HBT) fluorophore has attracted considerable attention in the field of fluorescence imaging, its short emission in the blue region and low quantum yield restrict its wide application. Herein, by mimicking the excited-state intramolecular proton transfer (ESIPT) effect, we designed a series of 2-(2-hydroxyphenyl)-benzothiazole (HBT) derivatives by complexing the heteroatoms therein with a boron atom to enhance the chance of the tautomerized keto-like resonance form. This strategy significantly red-shifted the emission wavelengths of HBT, greatly enhanced its quantum yields, and caused little effect on molecular size. Typically, compounds 12B and 13B were observed to emit in the near-infrared region, making them among the smallest organic structures with emission above 650 nm.

Detection to trace aluminum ion of pharmaceutical wastewater using synthesis of Schiff-based chemosensor

Background: The aim of this research was to develop a fluorogenic sensor for Al3+ions, which have been identified as a possible food and drinking water pollutant by the WHO and considered to be harmful to human health. Methods: The sensing mechanism was based on excited-state intramolecular proton transfer, with the intramolecular rotation restriction occurring after binding with the analyte. The probe attaches Al3+selectively and emits strong emission in 4:1 H2 O/MeOH (v/v) solution while irradiated at 400 nm in the presence of a wide number of cations, acting as a "turn-on" fluorescence chemosensor. The range of detection for Al3+is 3.3 nM (3 method), which is more than 200 times more responsive than the WHO suggested limit of 7.4 mM (3σ method). Mass spectra, job plot, and Benesi-Hildebrand plot were used to determine the formation of the 1:1 metal-to-ligand complex. Results: Aluminum (Al) ion content in effluent obtained from the pharmaceutical sector is 0.381 mM, which is a trace amount. A separate in vitro experiment indicates that the probe can precisely perceive Al3+ions in a cell line. The sensor-based method is developed to detect 3.3 nM of Al3+ions, which is significantly less than the WHO max. Conclusion: The probe to detect Al3+ions in live cells. HL becomes a flexible sensor for recognizing intracellular Al3+in human liver cancer cell line Hep G2 and human lung fibroblast cell lines by fluorescence cell imaging procedures, and the probe’s non-toxicity has been proven by MTT tests up to 100M.