On the role of functional groups in the formation of diazonium based covalent attachments: dendritic vs. layer-by-layer growth

Multilayered growth is often observed upon electrografting aryl diazonium derivatives on graphitic substrates due to the reactive nature of aryl radicals. The mechanism of the multilayer formation has been investigated either by measuring the thickness of the grafted layer, the charge transfer, or via simulations. Spectroscopy and in particular microscopy approaches are underrepresented. Herein, we demonstrate a comparative characterization of the multilayer growth of two diazonium derivatives on highly oriented pyrolytic graphite using a combination of cyclic voltammetry, atomic force microscopy, and scanning tunneling microscopy. While dendritic growth is observed for 4-nitro phenyl diazonium (4-NBD), 4-carboxy phenyl diazonium (4-CBD) shows layer-by-layer growth upon increasing the molecular concentration, revealing the impact of the functional groups on the growth mechanism.

Covalently Assembled Monolayers of Homo- and Heteroleptic FeII -Terpyridyl Complexes on SiOx and ITO-Coated Glass Substrates: An Experimental and Theoretical Study

Well-defined Fe^II -terpyridyl monolayers were fabricated on SiO_x and conductive ITO-coated glass substrates through covalent-bond formation between the metallo-organic complexes and a preassembled coupling layer. Three different homo- and heteroleptic complexes with terminal pyridyl, amine, and phenyl groups were tested. All the films were found to be densely packed and homogeneous, and consist of molecules standing upright. They exhibited high thermal (up to ≈220 °C) and temporal (up to 5 h at 100 °C) stability. The UV/Vis spectra of the monolayers showed pronounced metal-to-ligand charge-transfer bands with a significant redshift compared with the solution spectra of the metallo-ligands with a pendant pyridyl group quaternized with the coupling layer, whereas the shift was significantly smaller when the coupling layer was bonded to the primary amine (-NH₂ ) group of the complex. Cyclic voltammograms of the monolayers showed reversible, one-electron redox behavior and suggested strong electronic coupling between the confined molecules and the underlying substrate. Analysis of the electrochemistry data allowed us to estimate the charge-transfer rate constant between the metal center and the substrate. Additionally, detailed quantum-chemical calculations were performed to support and rationalize the experimentally observed photophysical properties of the Fe^II -terpyridyl complexes both in the solution state and when bound to a SiO_x -based substrate.

Metal-ions linked surface-confined molecular dyads of Zn-porphyrin–metallo-terpyridine: an experimental and theoretical study

Solid state molecular engineering is performed on SiOx-substrates by combining transition metal ions and metallo-porphyrins and terpyridyl complexes.

Synthesis of heteroleptic terpyridyl complexes of Fe(ii) and Ru(ii): optical and electrochemical studies

Heteroleptic terpyridyl complexes of Fe(ii) and Ru(ii) are synthesized. They are characterized using complimentary techniques and their optical and electrochemical properties are studied. A detailed computational study was also performed.