Pyridine-pyrazole based Al(iii) ‘turn on’ sensor for MCF7 cancer cell imaging and detection of picric acid†

We report herein the development of a new pyridine-pyrazole based bis-bidentate asymmetric chemosensor that shows excellent turn-on chelation-enhanced Al³⁺-responsive fluorescence. The presence of two ‘hard’ phenolic hydroxyl groups plays a pivotal role in switching-on the sensing through coordination to the ‘hard’ Al³⁺ ion, while the mechanism can be interpreted by the chelation-enhanced fluorescence (CHEF) process. The X-ray single structure show a planar conjugated structure of the ligand, which was further stabilized by extensive H-bonding and π–π stacking. The photophysical studies related to the sensing behavior of the titular ligand toward aluminum was investigated in detail using various spectroscopic techniques like UV-Vis, photoluminescence, fluorescence and time-correlated single-photon count (TCSPC) and time-resolved NMR. The spectroscopic methods also confirm the selective detection of Al³⁺ ion in the presence of other metal ions. The theoretical calculations using Density Functional Theory (DFT) and the Time Dependent Density Functional Theory (TD-DFT) provide further insight on the mechanistic aspects of the turn-on sensing behavior including the electronic spectra of both the ligand and the complex. Interestingly, the as-synthesized H₂DPC–Al complex can also be utilized as a fluorescence-based sensor for various nitroaromatics including picric acid, for which an INHIBIT logic gate can also be constructed. The as synthesized complex was subsequently used as a fluorescent probe for imaging of human breast adenocarcinoma (MCF7) cells using live cell confocal microscopic techniques.