Layer-by-Layer Deposition of Rh(I) Diisocyanide Coordination Polymers on Au(111) and Their Chemical and Electrochemical Stability

Abstract

The synthesis of electrode-attached Rh­(I) diisocyanide coordination polymers that incorporate a series of arylene diisocyanide linkers and which are grown from gold surfaces by a bottom-up, layer-by-layer procedure that allows for a high level of control for the film thickness is reported. A seed layer of the arylene diisocyanide ligand is used to template directional growth of the coordination polymer made using the well-studied square-planar rhodium tetrakis­(isocyanide) as the metal node. Materials ranging from 1 to 30 layers were prepared via layer-by-layer solution-phase deposition. Characterization of the polymer films using scanning electron microscopy and ellipsometry shows layer-by-layer control in these films with linear thickness growth per layer. Phase-modulated infrared reflection absorption spectroscopy (PM-IRRAS), diffuse reflectance UV–vis, and X-ray photoelectron spectroscopy (XPS) were used to confirm the structures of the films. Although prior reports of related coordination polymers and films based on diisocyanides showed considerable air-instability, the films reported here demonstrate significantly improved chemical stability and electrochemical stability at a moderately high applied bias. Electrochemical characterization and ex situ XPS demonstrate that these diisocyanide films are stable to stripping at potentials up to −2.2 V versus decamethylferrocene in acetonitrile, supporting their relevance for electrochemical applications.

Non-Covalent Interactions Mimic the Covalent: An Electrode-Orthogonal Self-Assembled Layer

“…We note that SEIRA data taken over this identical expanded potential range on Au surfaces exhibit minimal changes to the observed spectroscopic features (see Figure S30 and Table S8), consistent with the potential-dependent stability observed for the proposed C18-Fc self-assembled layer on glassy carbon surfaces in Figure . This window is larger than the documented values for thiol (−1.1 to 0.95 V), , N -heterocyclic carbene (−0.4 to 0.6 V), and isocyanide (−1.15 to 0.95 V) , modifications, as well as non-covalent immobilization strategies such as pyrene π–π stacking on carbon (−2.1 to 0.5 V). , We note that the potential stability window of the C18-Fc self-assembled layer is probed in the presence of C18-Fc in bulk solution. Thus, while the requirement to have C18-Fc present in the bulk solution limits the layer’s ex situ applications, under electrochemical conditions, provided that the synthesized amphiphile is soluble in the electrolyte of interest and does not degrade in the bulk solution, we show that the self-assembled layer is maintained in diverse electrochemical environments ( e.g.…”

“…We note that SEIRA data taken over this identical expanded potential range on Au surfaces exhibit minimal changes to the observed spectroscopic features (see Figure S30 and Table S8), consistent with the potential-dependent stability observed for the proposed C18-Fc self-assembled layer on glassy carbon surfaces in Figure 4. This window is larger than the documented values for thiol (−1.1 to 0.95 V), 18,21 N-heterocyclic carbene (−0.4 to 0.6 V), 21 and isocyanide (−1.15 to 0.95 V) 19,22 modifications, as well as non-covalent immobilization strategies such as pyrene π−π stacking on carbon (−2.1 to 0.5 V). 25,33 We note that the potential stability window of the C18-Fc self-assembled layer is probed in the presence of C18-Fc in bulk solution.…”

“…However, the reliance of specific covalent bond-forming events ( e.g. , using thiol, isocyanide, and carbene precursors) − on select metal surfaces (Au, Pd, Pt, Cu, Ag, and Hg) precludes generalizability across: (1) a wider range of electrode materials and (2) applied potentials due to competitive oxidative and reductive desorption. − While the use of π–π stacking of pyrene with carbon electrodes or diazonium grafting onto electrode surfaces has enabled systematic and tunable modifications, − these linkages are specific to their underlying electrode material and exhibit competitive potential-dependent desorption, electropolymerization, or multilayer formation. − The identification of new material compositions for electrochemical applications, namely, non-precious metal and metal-free electrodes, necessitates a general synthetic technology that is independent of the potential-dependent linkage stability in situ . Such a strategy would enable us to molecularly define the structure of the electrified interface without irreversibly modifying the electrode itself; this electrode-orthogonal approach would be agnostic to the surface chemistry of the electrode material yet retain the modular and predictive nature of covalent synthetic strategies.…”

“…As the layer is formed solely due to non-covalent interactions, self-assembly occurs on a wide array of electrode material compositions without permanent surface structural changes, i.e., the layer is removed by rinsing the electrode with water and can be restored by reintroduction of the amphiphile to the electrolyte. The in situ self-assembled layer is maintained in electrolytes that contain the amphiphile over potential ranges from −1.8 to 1.1 V vs Ag/AgCl, a window 0.9 V wider than the potential stability range of covalent linkers − and 0.3 V greater than existing non-covalent , linkers.…”

Layer-by-layer designer nanoarchitectonics for physical and chemical communications in functional materials

“…Since there are an extremely large number of substances with charge, many substances can be applied to this technique. The interactions are not limited to electrostatic interactions, but can be hydrogen bonds, 38 coordination, 39 charge transfer interactions, 40 stereocomplexation, 41 supramolecular inclusion, 42 biospecific recognition, 43 and many other interactions. 44 Thereby, many materials ranging from various polymers 45 to quantum materials, 46 colloidal particles, 47 two-dimensional materials, 48 biomolecules, 49 and viral particles 50 can be applied in layer-by-layer assembly.…”