Synthesis, Structural Characterization, and Sensing Properties of Clickable Unsymmetrical 1,1′-Disubstituted Ferrocene–Triazole Derivatives

A variety of unsymmetrically 1,1′-disubstituted ferrocenes 3 – 5 have been prepared by using the tandem click reaction/Staudinger-azaWittig process and their cation complexation properties studied using electrochemical and spectroscopic techniques. The common structural features present in these ligands are the presence of another redox unit, connected to the 1-position of the central ferrocene core through a triazole ring, and a photoactive moiety linked to the 1′ -position of such core through an imine group. Receptors 3 and 5 undergo perturbation of the CV in the presence of Pb 2+ and Zn 2+ cations, whereas receptor 4 undergoes a different type of perturbation in the presence of Ni 2+, Cd 2+, Zn 2+, and Pb 2+ cations. The low-energy band of the absorption spectra of receptor 3 is blue-shifted, upon addition of Zn 2+, and Pb 2+ cations, whereas receptor 4 in the presence of Ni 2+ and Cd 2+ undergoes a remarkable red shift (Δλ = 110 nm) of the LE band which is responsible for the change of color from red to blue. Moreover, receptor 3 underwent a significant increase in its emission band in the presence of Pb 2+, whereas in receptor 5, such an increase is notably lower. In conclusion, receptor 4 behaves as a colorimetric receptor for Ni 2+ and Cd 2+ and 5 acts as a selective fluorescent receptor for the Pb 2+ cation. On the basis of the 1 H NMR titration data and from the DFT theoretical calculations, tentative binding modes have been proposed for the metal complexes formed.