Binding ability of first and second generation/carbazolylphenyl dendrimers with Zn(II) tetraphenylporphyrin core towards small heterocyclic substrates
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A study of complex formation of Zn(II) tetraarylporphyrin dendrimers with carbazolylphenyl branches towards 1,4-diazabicyclo-[2.2.2]octane, pyridine, imidazole, N-methylimidazole and 1,2,3-triazole was carried out by spectrophotometric and H-1 NMR titration methods. It has been shown that the binding ability of the porphyrin receptors towards mono and bidentate N-containing substrates depends on the nature, number and generation of the branches. Bulky substituents are able either to significantly reduce the binding ability of the tetrapyrrolic cores due to the shielding of the porphyrin reaction centres, or to significantly increase it by forming intramolecular cavities for complementary binding of substrates. It has been determined that due to a good geometric match of the ligand's size with the size of the intramolecular cavities of the porphyrin receptors, and by the existence of additional hydrogen bonding and/or pi-pi interactions between the ligand and the triazole fragments of the porphyrin the Zn-tetraarylporphyrins with eight 4-carbazolylphenyl-1,2,3-triazole end groups of the first and the second generations could be used as effective receptors for imidazole, N-methylimidazole and 1,2,3-triazole. Taking into account the fact that binding is accompanied by a clear and easily identifiable response in the UV-Vis spectra of the reaction mixture, these metalloporphyrins could be considered as molecular optical sensing devices for small heterocyclic substrates.