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Synthesis and Spectroscopic Study of N2O2 Aza-Crown Macrocyclic Ligands Decorated by Benzimidazole Side Arm

Zamani, Pardis | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58545 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Ghanbari, Bahram
  7. Abstract:
  8. In the present project, the synthesis of two new aza-crown macrocycles with a benzimidazole side arm with an asymmetric (L1) and symmetric (L2) configuration was carried out. The structures of these macrocycles were identified using 1H NMR, 13C{H}NMR, FT-IR, UV-Visible, fluorescence and elemental analysis, and in the case of macrocycle L2, crystallography with X-ray diffraction was used to determine the structure. The study of the UV-Visible spectrum of macrocycle L1 in the presence of a series of chloride salts of different cations demonstrates the unique and selective interaction of this macrocycle with Fe(Ⅲ). Since the interaction of this ligand with the trivalent iron cation causes a color change of its solution in ethanol from yellow to purple, it was introduced as a chromogenic chemosensor for Fe(Ⅲ). The coordination chemistry study of this interaction in solution (ethanol:water with a molar ratio of 9:1) was carried out using the Job plot, formation constants and viscosity changes. Also, to complete the results, 1H NMR titration was performed in deuterated dimethyl sulfoxide solvent. Although the results obtained from the Job indicate the dominance of a 2:1 molar interaction of the ligand and cation in the solution state, the results obtained from the supramolecular site calculations and viscosity changes indicate that other molar ratios also exist in the solution state. The formation constant and the detection limit for this ligand with the corresponding cation are reported to be 3.43 × 103 M-1 and 0.23 µM, respectively. In addition to the studies carried out in the solution state, the identification of the L1 macrocycle complex with Fe(III) was carried out by elemental analysis and ICP, which according to these results confirmed the 2:1 molar interaction of the macrocycle with Fe(III) in the solid state. The emission properties of macrocycle L2 were further studied in the presence of the aforementioned cations using fluorescence spectroscopy. The emission intensity of macrocycle L2 increases in the presence of Cr(Ⅲ) cation, which indicates the selectivity of this macrocycle for Cr(Ⅲ) cation even in the presence of other cations in the form of chloride salts. The detection limit for ligand L2 with the corresponding cation is calculated to be 1.04 μM. The results obtained from 1H NMR titration of this macrocycle in deuterated dimethyl sulfoxide solvent as well as absorption and emission spectroscopy studies in solvent (ethanol:water with a molar ratio of 8:2) indicate the simultaneous participation of the two parts of the macrocycle ring and its benzimidazole arm in this interaction. In addition, the study of the behavior of macrocycle L2 in the presence of different anions of sodium salt indicates the selectivity of this ligand towards chromate ion. The results of 1H NMR titration clearly show that only the side arms are involved in this interaction. To complete the studies, DFT calculations were used to investigate the energy levels and suitable positions in the macrocycle structure for interaction with ions, which were in agreement with the experimental results. The extinction constant and detection limit for this ligand with the corresponding ion are reported to be (4.48 ± 0.29)103 M-1 and 0.18 μM, respectively
  9. Keywords:
  10. Macrocyclic Ligand ; Fluorescence ; Density Functional Theory (DFT) ; Fluorescence Sensors ; Benzimidazol ; Side Arms ; Cationic Sensors

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