Dye displacement assays are a simple but effective method to determine the concentration of target analytes. Previously, we have shown that phenylboronic acid pinacol ester hydrogels (borogels) can be used to develop a boronic acid–Alizarin red S dye displacement assay for the determination of fructose (orange to red). In this work, benzoxaborole hydrogels (BOBgels) were developed, and these BOBgels demonstrated an enhanced apparent binding affinity towards monosaccharides, in particular towards glucose.

In the title compound, C₉H₁₀ClNOS, the amide functional group –C(=O)NH– adopts a trans conformation with the four atoms nearly coplanar. This conformation promotes the formation of a C(4) hydrogen-bonded chain propagating along the [010] direction. The central part of the molecule, including the six-membered ring, the S and N atoms, is fairly planar (r.m.s. deviation of 0.014). The terminal methyl group and the C(=O)CH₂ group are slightly deviating out-of-plane while the terminal Cl atom is almost in-plane. Hirshfeld surface analysis of the title compound suggests that the most significant contacts in the crystal are H...H, H...Cl/Cl...H, H...C/C...H, H...O/O...H and H...S/S...H. π–π interactions between inversion-related molecules also contribute to the crystal packing. DFT calculations have been performed to optimize the structure of the title compound using the CAM-B3LYP functional and the 6–311 G(d,p) basis set. The theoretical absorption spectrum of the title compound was calculated using the TD–DFT method. The analysis of frontier orbitals revealed that the π–π* electronic transition was the major contributor to the absorption peak in the electronic spectrum.

2ʹ-(2-((4-(methylthio)phenyl)amino)-2-oxoethoxy)-[1,1ʹ-biphenyl]-2-yl 5(dimethyl amino)naphthalene-1-sulphonate (1) was synthesised and used as a F⁻ ion sensor. The selectivity of sensor 1 with various anions (F⁻, Cl⁻, Br⁻, CH₃COO⁻, C₆H₅COO⁻ and H₂PO₄⁻) in DMSO was evaluated by ¹H NMR, UV-visible and fluorescence study. For ¹H NMR, an amide proton of sensor 1 disappeared due to the deprotonation reaction upon addition of F⁻ ion. On the contrary, the proton signal of HF₂⁻ emerged at 16.11 ppm. Upon addition of F⁻ ion, sensor 1 showed a new absorption band at 300 nm and the solution turned colourless. For fluorescence response, sensor 1 exhibited the enhancement of emission intensity at 434 nm with slight blue shift when titrated with F⁻ ion. These results suggest that sensor 1 possessed high sensitivity and selectivity towards F⁻ ion detection. In addition, the sensor 1 test strip coated on TLC plates and filter papers were demonstrated for specific detection F⁻ ion. Graphical abstract

3,5-Dihydroxyphenyl-5-(dimethylamino)naphthalene-1-sulfonate, also referred to as sensor R1, was synthesized and characterized by ¹H- and ¹³C-NMR, IR, HRMS, and single-crystal X-ray diffraction. Connections in the packing crystal structure of sensor R1 occur through hydrogen bonding interactions. However, no π-π stacking interactions between molecules of sensor R1 were observed. Addition of fluoride ion to a solution of sensor R1 resulted in the appearance of a new absorption band at 310 nm, which corresponded to the deprotonated species, and quenching of the peak at an emission wavelength of 562 nm. For the addition of other anions, there was a slight decrease in corresponding peaks in the UV-visible and emission spectra of sensor R1. According to the ¹H-NMR study, the aromatic proton resonances of sensor R1 shifted upfield when adding fluoride ion. Analysis of the solutions prepared using Job’s method revealed that the complexation ratio of the complex formed between sensor R1 and fluoride ion was 1:1. The Stern−Volmer quenching constant (K_sv) between sensor R1 and fluoride ion was characterized as 7157 M⁻¹.

In this study, 2-(3-(hexyloxy)-5-methylphenoxy)-N-(4-nitrophenyl)acetamide (sensor L1) was synthesized and characterized by FT–IR, ESI–MS, ¹H and ¹³C NMR spectroscopy, elemental analysis, and single crystal X-ray techniques. The crystal structure and space group of sensor L1 was monoclinic and P2₁, respectively. The crystal packing of sensor L1 was dominantly linked by two strong hydrogen bonds forming a six membered ring pattern. The binding properties of sensor L1 and various anions (F⁻, Cl⁻, Br⁻, CH₃COO⁻, C₆H₅COO⁻, and H₂PO₄⁻) were investigated by UV–Vis and ¹H NMR spectroscopy in DMSO. The proton resonance signals of sensor L1 and F⁻ greatly changed positions when compared to those of anions. The solution color of sensor L1 changed from pale yellow to orange in the presence of F⁻. The UV–Vis results indicate that sensor L1 and F⁻ ions underwent an internal charge transfer process. The stoichiometric complex was confirmed by Job’s method, revealing a 1:1 formation for sensor L1 and fluoride. Our results show that sensor L1 is highly selective for fluoride ions over other anions.

The complete molecule of the title compound, C₃₀H₂₉N₃O₅S₂, is generated by a crystallographic twofold axis: the O atom and NH group attached to the central benzene ring are statistically disordered. The dihedral angle between the naphthalene ring system and the central benzene ring is 52.99 (6)°, while the pendant naphthalene ring systems subtend a dihedral angle of 68.17 (4)°. An intramolecular C—H...O hydrogen bond closes anS(6) ring. In the crystal, the molecules are linked by weak C—H...O hydrogen bonds.