A multisensing ratiometric fluorescent sensor for recognition of Al3+, Th4+ and picric acid

The ratiometric fluorescence sensor of 5-(1H-pyrrol-2yl)-7, 8, 13, 14-tetrahydrodibenzo [a,i]phenanthridine (4a), a ligand with blue emission, was introduced for the quantitative recognition of Al3+ and Th4+ ions and picric acid using absorption and emission spectroscopic techniques. We investigated the unique recognition of Al3+ and Th4+ ions and picric acid by 4a using the studies of UV-vis absorption and fluorescence spectroscopy in acetonitrile as solvent. There was a marked color change from blue to green at 365 nm UV light. High binding constant values (Ka) of 1.175 x 107 M-1 for Al3+ ions and of 3.233 x 106 M-1 for Th4+ ions, 4.3093 x 104 M-1 for picricacid respectively were exhibited by the sensor 4a. The interference studies showed the existence of high selectivity and sensitivity for the probe 4a towards Al3+ and Th4+ ions over other competing cations. Ligand 4a interacted with Al3+ and Th4+ ions to create a 1 : 1 complex, and 1H NMR titration and Job's plot studies confirmed this mechanism further. The sensor 4a had many advantages like low detection limits (LOD) of 38.7 nM and 70.5 nM and 0.53 nM towards Al3+ and Th4+ ions, picricacid and fast reaction. The sensing can be carried out in a wide pH range of 3 to 11. The real time application of 4a was effectively verified by the determination of Al3+ and Th4+ ions and picricacid in paper strips test and also in different water samples.