New Sulfur‐Containing Ferrocenylimidazo[4,5‐b]pyridines: Multiresponsive Hg²⁺ Ion Sensing and Structure‐Sensing Correlation

Abstract

Two new sulfur-containing ferrocenylimidazo [4,5-b]pyridines, 2-ferrocenyl-5-(thiophen-2-yl)-1H-imidazo [4,5-b]pyridine (L1) and 2-ferrocenyl-5-(thiophen-3-yl)-1H-imidazo[4,5-b]pyridine (L2), were synthesized and characterized. L1 and L2 behaved as highly selective fluorescent "turn-off", redox (ΔE 1/2 = 0.25 V for L1 and ΔE 1/2 = 0.22 V for L2) and UV active receptors for Hg 2 + ions through the formation of the corresponding 2 : 1 and 1 : 1 (receptor:metal ion) complexes, with detection limits 4.47 × 10 À 8 M and 2.21 × 10 À 7 M, respectively. Furthermore, the quenched fluorescence of L1 was recovered on iodide ion addition. The sensing mechanism study suggested that although the imidazo[4,5-b]pyridine is the main coordination unit providing N, N binding sites, the added thienyls have improved the fluorescence emission and Hg 2 + sensing selectivity of L1 and L2, and obviously influenced the coordination mode. Finally, living cell imaging and test strip experiments demonstrated the potential application of L1 in fluorescent visualization of Hg 2 + ions in biological and environmental systems.

Imidazopyridine Family: Versatile and Promising Heterocyclic Skeletons for Different Applications

“… Imidazo[1,5- a ]pyridines are investigated and utilized for their emissive properties (serving as fluorophores) [ 13 , 14 , 15 ] or chelating ligands for metallic ions, contributing to the development of on–off-type sensors [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Imidazo[4,5- b ]pyridines are principally studied for the development of emissive products for OLEDs (organic light-emitting diodes) and sensor applications due to their excellent emissive properties [ 23 , 24 , 25 , 26 , 27 , 28 ]. Imidazo[4,5- c ]pyridines display a bioisosteric resemblance to the purine nucleus, manifesting similar structural and electronic properties.…”

“…Imidazo [4,5-b]pyridines are principally studied for the development of emissive products for OLEDs (organic light-emitting diodes) and sensor applications due to their excellent emissive properties [23][24][25][26][27][28]. 4.…”

Metal‐ion sensor composed of self‐assembled monolayer of amine ligand formed by the use of molecular tripod

“…The formation of a tight 1:1 adduct by the coordination of the imidazolic basic nitrogen to Pb 2+ , strengthened by the nitrogen atom in the fused pyridine ring, was revealed by the Job's plot, NMR chemical shift changes, and DFT calculations. The utility of this structural unit has been confirmed by the studies on a series of related ionophores, which frequently exhibited a multichannel response to metal ions [1–6].…”

“…Among the sensing molecules, a number of nitrogenand sulfur-containing heterocycles have been reported to show selective coordination properties toward specific metal ions [1][2][3][4][5][6][7]. Molina reported that imidazopyridine bearing a ferrocenyl group 1 acts as a triple-channel sensing ionophore, which on addition of Pb 2+ shows a redox potential shift, color change, and fluorescence enhancement [8].…”