2-Ferrocenylimidazole-based multiresponsive receptors for Al3+, Cu2+, and H2PO4− ions: Effect of structural modification on the ion sensing performance

Abstract

Two 2-ferrocenylimidazoles decorated with two pyridyl arms, 2-ferrocenyl-4,5-di(2-pyridyl)-1H-imidazole (L1) and 2-ferrocenyl-4,5-di(3-pyridyl)-1H-imidazole (L2), have been synthesized as potential multichannel ditopic receptors for cations and anions, owing to the presence of redox, chromogenic and fluorescent groups at the imidazole core. The structures of L1 and its Ag(I) complex (I) [L12·Ag2·(NO3)2] were further confirmed by X-ray crystal analysis. The most salient features derived from sensing studies are that L1 behaves as a highly selective fluorescent “turn-on” receptor for Al3+ and Cu2+ cations, whereas L2 acts as a dual fluorescent “turn-on” and redox selective receptor for H2PO4− anions. This significant change in fluorescent sensing selectivity is due to the change in the relative position of N atoms in the pyridyl groups. Furthermore, the resulting complexes of L1-Al3+ and L1-Cu2+ systems are able to detect Br− and I− by color changes. The sensing mechanism and binding mode of these two receptors were confirmed by titration spectra and ESI-MS. Finally, living cell imaging experiments demonstrated the value of L1 in the fluorescent visualization of Al3+ ions in biological systems.