Opto-Electroactive Amino- and Pyridyl-Terminated Monolayers of RuII–Terpyridyl Complexes and Their Usage as Hg2+ Sensors

Robust opto-electroactive monolayers of three different Ru II –terpyridyl complexes with amino and pyridyl termination are fabricated on SiO x -based substrates using siloxane-based attachment chemistry and either pyridyl or amine linkage to the preliminary prepared template. The UV–vis spectra of these monolayers display the characteristic metal-to-ligand charge-transfer bands, with a bathochromic shift compared to the spectra of the respective metalloligands dissolved in acetonitrile solution. This shift is notably larger for the pyridyl-linked monolayers compared to the amino-linked film, correlating qualitatively with the molecular grafting density. Cyclic voltammograms of the monolayers covalently attached onto indium tin oxide electrodes show reversible switching between the two redox states (Ru 2+ to Ru 3+ and vice versa), with a typical one-electron redox behavior. The sensing response of the monolayers to a series of different metal ions was tested, with the amino-decorated films showing a particularly high sensitivity to Hg 2+ and a close-to-linear response to this analyte in the ppm concentration range.