Highly Selective and Sensitive Visual Detection of Fe³⁺ using a Simple Quinazoline-Based Colorimetric Sensor

Among the various cations, the Fe³⁺ ion is one of the most critical transition metal ions in living cells for many cellular functions and enzymatic activities. The decrease or overloading of Fe³⁺ can lead to different disruptions in humans. Also, Fe³⁺, highly toxic, is very common in all industrial wastewater. So, the design and synthesis of Fe³⁺ chelators as high-selective chemosensors are essential for detecting Fe³⁺. In this paper, 6-(6-bromopyridin-2-yl)benzo[4,5]imidazo[1,2-c]quinazoline (BQ) as a novel colorimetric sensor for sensing of Fe³⁺ was synthesized and characterized by ¹H-NMR, ¹³C-NMR, IR, and mass spectrometry. The sensing behavior of BQ toward various cations has been analyzed via colorimetric detection and UV-vis spectroscopy. The BQ was observed to have excellent selectivity and sensitivity to the presence of Fe³⁺ among the tested ions in aqueous media. Interestingly, the BQ can selectively recognize Fe³⁺ ions with the naked eye via the color change of colorless to yellow. The effect of pH on the stability and absorption of BQ towards Fe³⁺ was studied. The results of pH studies showed that the absorbance of complex BQ/Fe³⁺ remains stable between pH 5-10. Moreover, to determine the sensing behavior of BQ to Fe³⁺, the mole ratio method was carried out. The binding stoichiometry of BQ/Fe³⁺ was assessed by using Job's plot and indicated the 1:1 binding ratio between BQ and Fe³⁺. Under the optimal conditions, there was a good linear relationship (correlation coefficient R² = 0.9886) in Fe³⁺ concentration in the 58-114 μM range, with a detection limit of 53.39 nM.