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Base Study for the Development of a Cyclohexane Based Tripodal Molecular Device as "OFF-ON-OFF" pH Sensor and Fluorescent Iron Sensor


Vijay Dangi, Minati Baral* and B. K. Kanungo  


Base studies have been performed for a cyclohexane based tripodal molecular device, that acts as highly selective pH and fluorescence iron(III) sensor. The biomimetic analog of microbial siderophore from quinolobactin was designed by implementing hydroxyquinoline binding sites to a backbone of cyclohexane through an amide linked rigid spacer. The tripodal probe exhibits an OFF-ON-OFF fluorescence sensor in different pH conditions. The molecule showed good selectivity for Fe(III) ions among Al(III), Fe(III), Cr(III), Co(II), Fe(II), Ni(II), Zn(II), Cu(II), Mn(II) and Pb(II) in a highly aqueous medium. A significant quenching in the emission spectra was displayed in the water-DMSO mixture (9:1) at the environmental pH that enables its potential use to act as a fluorescent sensor for the detection of Fe(III) ion with detection limit 2.4 × 10-6 M. A prominent hyperchromic effect was exhibited in the presence of Fe(III) ions in a neutral medium. The plausible mechanism and the photophysical performance were established by DFT. The theoretical results showed agreement with the experimental ones. The chemical hardness of various forms of the ligand in different pH conditions viz; protonated (LH+), neutral (L) and deprotonated (L-), and its Fe(III) complex in neutral form were determined in gas phase which indicated that the complex formed with its acidic form is more stable as compared to the complexes of its neutral and basic forms having favored by protonation at N-atom of the pyridoxal moieties which also inspires a d-PET mechanism leading to a fluorescence quenching.


Tripodal; Sensor; OFF-ON-OFF; DFT; ZINDO; PET


Department of Chemistry, National Institute of Technology, Kurukshetra, Haryana-136119, Department of Chemistry, National Institute of Technology, Kurukshetra, Haryana-136119, Department of Chemistry, Sant Longowal Institute of Engineering & Technology, Longowal- 148106

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