Fabrication of multilayer films of viologen on a glassy carbon electrode by bottom-up layer-by-layer assembly

Electroreduction of Viologen Phenyl Diazonium Salts as a Strategy To Control Viologen Coverage on Electrodes

A majority of the reported electrografting of aryldiazonium salts result in the formation of covalently attached films with a limited surface coverage of below 5 nmol·cm^-2. Herein, we report the preparation of higher-thickness redox-active viologen-grafted electrodes from the electroreduction of viologen phenyl diazonium salts, by either cyclic voltammetric (CV) sweeps or electrolysis using a fixed potential. Both of the methodologies were successfully applied for various conductive surfaces, including glassy carbon (GC), gold disc, indium tin oxide glass, mesoporous TiO₂ electrodes, and 3D compacted carbon fibers. A robust maximal viologen coverage, Γ_viologen = 9.5 nmol·cm^-2, was achieved on a GC electrode by CV electroreduction. Electroreduction held at a fixed potential at E_appl. = -0.3 V can fabricate viologen-grafted electrodes with Γ_viologen in the range of 0-37 nmol·cm^-2 in a controllable way, by simply adjusting the electrodeposition time t_appl.. Time-dependent Γ_viologen were found to be 10 nmol·cm^-2@2 min, 20 nmol·cm^-2@4.2 min, and 30 nmol·cm^-2@7 min. Furthermore, a TiO₂ electrode coupled with Γ_viologen of 140 nmol·cm^-2 exhibited electrochromic performance, with the color changing from pale yellow to blue and red brown.

π-Conjugated bis(terpyridine)metal complex molecular wires

Bottom-up approaches have gained significant attention recently for the creation of nano-sized, ordered functional structures and materials. Stepwise coordination techniques, in which ligand molecules and metal sources are reacted alternatively, offer several advantages. Coordination bonds are stable, reversible, and self-assembling, and the resultant metal complex motifs may contain functionalities unique to their own characteristics. This review focuses on metal complex wire systems, specifically the bottom-up fabrication of linear and branched bis(terpyridine)metal complex wires on electrode surfaces. This system possesses distinct and characteristic electronic functionalities, intra-wire redox conduction and excellent long-range electron transport ability. This series of comprehensive studies exploited the customizability of bis(terpyridine)metal complex wires, including examining the influence of building blocks. In addition, simple yet effective electron transfer models were established for redox conduction and long-range electron transport. A fabrication technique for an ultra-long bis(terpyridine)metal complex wire is also described, along with its properties and functionalities.