A Chemosensor of 1,8-Dihydroxyanthraquinone PMOs Prepared in a Ternary Deep Eutectic Solvent for the Sensitive Detection of Cu2+

A novel type of organic-inorganic hybrid periodic mesoporous materials based on 1,8-dihydroxyanthraquinone (DHAQ-PMOs) was synthesized in a ternary deep eutectic solvent (DES). In the process of the material synthesis, an organosiloxane precursor (DHAQ-Si) and tetraethylorthosilicate (TEOS) were used as the mixed Si source, and cetyltrimethylammonium bromide (CTAB) was used as the structure directing agent. The DES formed by choline chloride (ChCl), urea (U), and ethylene glycol (EG) was used as a green solvent. The water needed for the hydrolysis of DHAQ-Si and TEOS was provided from free water in the sodium hydroxide solution. As characterized by small-angle X-ray scattering, nitrogen adsorption/desorption isotherms, and high-resolution transmission electron microscopy, the obtained mesoporous materials exhibit a two-dimensional hexagonal (P6mm) structure. DHAQ possesses double fluorescence emission peaks at ca. 520 and 580 nm due to the effect of the excited-state intramolecular proton transfer (ESIPT). For DHAQ-PMOs, the silica framework can provide a rigid environment that makes the fluorescence properties more stable and the fluorescence emission peak appears to red-shift obviously. The DHAQ-PMOs have high selectivity and sensitivity in a wide pH range that can be used to detect Cu2+, and the limit of detection (LOD) is as low as 2.39 × 10-9 M. Fluorescence polarization experiments, high-resolution mass spectrometry, and Fourier transform infrared spectroscopy were used to study the coordination interaction between DHAQ and Cu2+. The density functional theory (DFT) was used to further prove the coordination ability and interaction between DHAQ and Cu2+. XPS spectra were also done to prove the coordination of DHAQ and DHAQ-PMO-10 with Cu2+. In addition, confocal fluorescence microscope images exhibit that DHAQ-PMOs can detect Cu2+ in living cells. The results show that DHAQ-PMOs have great application potential as a sensor for the detection of Cu2+.