A rhodamine B based chemosensor for selective detection of Al 3+ion: Photophysical investigations and analysis in real samples

Abstract

A rhodamine based chemosensor 1 was synthesized, characterized through various spectroscopic techniques and their photophysical spectral pattern was analyzed in presence of various metal ions. The UV-Vis absorption and fluorescence studies showed that the colourless and non-fluorescent solution of the compound remained so in presence of many metal ionic inputs, i.e. Na + , Cr 3 + , Mn 2 + , Fe 2 + , Fe 3 + , Co 2 + , Ni 2 + , Cu 2 + , Zn 2 + , Pb 2 + , Cd 2 + and Hg 2 + , whereas addition of Al 3 + ion led to change in colour of the solution to magenta and high fluorescence. The probe metal complexation pattern was estimated as 1:1 complexation stoichiometry of 1 with Al 3 + ion, which was well supported by ESI-MS and FTIR spectra. The quantum chemical calculations with DFT revealed that complexation with Al 3 + lowered the HOMO-LUMO energy gap in 1 , and HOMO -> LUMO + 3 energy differences in the complex corresponded to its observed complexation-induced electronic transition. Input competitive experiments inferred to the selectivity preferences towards Al 3 + ion, as the fluorescence intensity of 1 with Al 3 + ion remained unperturbed on subsequent presence of other potential metal ions. The 'turn-on' photophysical signaling pattern of the complex could be reversed in subsequent presence of few counter anions and chelating ligands. The potential utility of 1 in detection of Al 3 + was demonstrated in real samples and operation of molecular logic functions.