Imidazole/benzimidazole-modified cyclotriphosphazenes as highly selective fluorescent probes for Cu²⁺: synthesis, configurational isomers, and crystal structures

Abstract

Configurational isomers (cis and trans) of imidazole- or benzimidazole-modified cyclotriphosphazenes (3a, 4a or 3b, 4b) were designed, synthesized and investigated as fluorescent probes for metal ions. The newly synthesized compounds were characterized by H andP NMR, and MALDI MS spectrometry. The configurations of geometric isomers were analyzed by X-ray crystallography and P NMR spectroscopy on addition of CSA. The photophysical behaviour and metal ion selectivity of the compounds were investigated by UV/vis and fluorescence spectroscopy. Among the examined 20 metal ions, the fluorescence emissions of the isomer mixtures were quenched by Cu together with Fe, Fe, Zn and Ni ions, but each individual isomer (3a,b and 4a,b) exhibited an on-off-type fluorescence response with high selectivity towards only Cu with a low limit of detection ranging from 1.27 μM to 2.04 μM. The complex stoichiometries of 3a,b and 4a,b with Cu were determined as 1 : 1 (L/M) using the method of continuous variation (Job's plot) and density functional theory (DFT) calculations; moreover the complex formation of 4a with Cu was unambiguously determined by X-ray crystallographic analysis that is consistent with the results obtained by the Job's plots as well as DFT.

Synthesis of new cyclotriphosphazene derivatives bearing Schiff bases and their thermal and absorbance properties

“…The molar absorption coefficients of 3a-3d were as high as 10 4 to 10 5 L mol −1 cm −1 , which were determinative for ππ * state transition characteristics of cyclotriphosphazene derivatives (3a-3d) [52]. These obtained results are quite reasonable because it is well known that cyclophosphazenes are optically inert in the UV-Vis region and their photophysical properties can be adjusted according to the appended moiety [10,[53][54][55].…”

Multisite Coordination Ligands on Cyclotriphosphazene Core for the Assembly of Metal Clusters and Porous Coordination Polymers

“…The cis ‐isomer of non‐geminal benzimidazolyl CTP ligand 88 has been treated with CuCl 2 in order to synthesize (Scheme 21) the respective copper complex 89 [90] . In complex 89 , the two ligands of CTP anchored with pair of benzimidazole have been connected via bridging Cu 2 Cl 2 .…”

Pyrene-BODIPY-substituted novel water-soluble cyclotriphosphazenes: synthesis, characterization, and photophysical properties

“…In both spectra, molecular ion peaks were related to the calculated values. 31 P NMR spectra of compounds 6 and 7 were shown as the AB 2 spin system, owing to the different environments of the 2 different phosphorus atoms on the cyclotriphosphazene ring (Figure 3). However, it was not possible to calculate the coupling constants due to the complexity of the spectra.…”

“…The absorption and fluorescence spectra of 6 and 7 were similar to the pyrene-substituted BODIPY precursors, since the DEGME moiety did not have any optical properties in the UV-Vis region. It is well known that cyclotriphosphazenes are optically transparent in the UV-Vis region and their photophysical properties can be adjusted according to an attached moiety [31,32]. Absorptions and emissions of compounds 6 and 7 and their precursor BODIPYs (4 and 5) were investigated in THF, which is a good solvent for all compounds, at a concentration of 1 × 10 −6 M. As can be seen in Figures 13 and 14, the difference between the absorption and emission maxima of compounds 4 and 6 was 9 nm.…”