This article discusses the design and analysis of a new chemical chemosensor for detecting mercury(II) ions. The chemosensor is a hydrazone made from 4-methylthiazole-5-carbaldehyde and fluorescein hydrazide. The structure of the chemosensor was confirmed using various methods, including nuclear magnetic resonance spectroscopy, infrared spectroscopy with Fourier transformation, mass spectroscopy, and quantum chemical calculations. The sensor’s ability in the highly selective and sensitive discovery of Hg²⁺ ions in water was demonstrated. The detection limit for mercury(II) ions was determined to be 0.23 µM. The new chemosensor was also used to detect Hg²⁺ ions in real samples and living cells using fluorescence spectroscopy. Chemosensor 1 and its complex with Hg²⁺ demonstrate a significant tendency to enter and accumulate in cells even at very low concentrations.

The electronic and molecular structures of metal-free tetrabenzoporphyrin (H₂TBP) and its complexes with zinc, cadmium, aluminum, gallium and indium were investigated by density functional theory (DFT) calculations with a def2-TZVP basis set. A geometrical structure of ZnTBP and CdTBP was found to possess D_4h symmetry; AlClTBP, GaClTBP and InClTBP were non-planar complexes with C_4v symmetry. The molecular structure of H₂TBP belonged to the point symmetry group of D_2h. According to the results of the natural bond orbital (NBO) analysis, the M-N bonds had a substantial ionic character in the cases of the Zn(II) and Cd(II) complexes, with a noticeably increased covalent contribution for Al(III), Ga(III) and In(III) complexes with an axial –Cl ligand. The lowest excited states were computed with the use of time-dependent density functional theory (TDDFT) calculations. The model electronic absorption spectra indicated a weak influence of the nature of the metal on the Q-band position.