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

Abstract

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 aminolinked 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.

Two‐Dimensional Photosensitizer Nanosheets via Low‐Energy Electron Beam Induced Cross‐Linking of Self‐Assembled RuII Polypyridine Monolayers

“…The latter serves as reference spectrum and was recorded from a stack of eight layers to increase the inherently low signal to noise ratio of individual only ≈1 nm thick nanosheets. Calculating the spectral differences between the absorption of both nanosheets (red), reveals characteristic metal‐to‐ligand charge transfer (MLCT) absorption features at ≈530 nm, similar as reported for the SAMs of Ru II polypyridine compounds on glass [23] or ITO [24] . Compared to the spectrum of 1 in CHCl 3 solution the absorption band of Ru II CNM 2 b is broader and shifted to longer wavelengths.…”

Siloxanes—Versatile Materials for Surface Functionalisation and Graft Copolymers

“…Glass, ITO and Si (100) wafer surfaces were modified with Ru 2+ terpyridyl complexes, in order to produce materials for Hg 2+ sensing [ 13 ]. First, the substrate surfaces were treated with an iodo-functionalised trimethoxysilane, utilising its reaction with the hydroxyl groups present on those surfaces.…”

“…The Si-O bond is a highly versatile chemical linkage that can be found in a great variety of materials and molecules, linking together inorganic [ 1 , 2 , 3 ] and organic species [ 4 , 5 , 6 ], as well as being a building block for polymers [ 7 , 8 , 9 ] and sophisticated 3D oligomers [ 10 , 11 ]. In the role of linkage, the siloxane bond is robust, chemically resistant to an array of environments and easily established, e.g., via the reaction of silanes with organic or inorganic hydroxyl groups [ 6 , 12 , 13 ]. Conversely, systems containing repeating siloxane bonds—polysiloxanes—tend to exhibit good mechanical properties (ranging from elastomeric to more rigid, dependent on the molecular weight of the polymers, introduced substituents and the use of cross-linking reactions), medium-high solubility in common organic solvents, self-assembling and film-forming properties, as well as low dielectric constants and, frequently, biocompatibility [ 14 ].…”

Compositionally Controlled Electron Transfer in Metallo-Organics

“…Electron hopping and more recently a “stepping-stone mechanism” (=modified tunneling process) were proposed. , Assemblies having reversible electron transfer to unidirectional current flows and even charge trapping have been demonstrated . Reversible changes in the metal oxidation state, along with concurrent large variations in their light absorption efficiency, have resulted in potentially useful electrochromic coatings. , Electrocatalysis, sensing, and antibacterial properties have been reported as well as supercapacitors, electrochromic devices, and inverted solar cells. − Such films have also been shown to mimic the characteristics of conventional electronic circuits, including flip-flops. , The functionalities of metal–organic films can be controlled by sequence-dependent assembly, that is, depositing nanoscale layers consisting of isostructural complexes with different metal cations. ,, …”