Viologens are a group of electroactive organic electrolytes and generally change from colorless to blue or violet after the first reductive reaction, thus they have attracted much attention in the fields of chemically modified electrodes, electrochromic display and supramolecular devices. The alkyl substituents in the viologens are easily functionalized (oxosilane or thiol), resulting in the as-prepared viologens suitable for potential candidates to construct well-defined thin films, multilayers or molecular aggregates by the bottom-up techniques, such as the Langmuir-Blodgett (LB) films, self-assembled monolayers (SAMs) and layer-by-layer (LBL) assembly. If the alkylated substituents contain a thiol or silane substituent, the viologens produced can form SAMs on the solid surfaces, while if they are long alkyl chains, the amphiphilic viologens can form stable insoluble monolayers at the air-water interface and be deposited on the substrate surfaces to form the LB films. The poly(viologen) derivatives can form LBL multilayers with negatively charged polyelectrolytes or nanostructural materials including carbon nanotubes. This paper reviews recent developments in the design and assembly of viologen-functionalized supramolecular and nanoscale materials by the molecular assembling methods. The optical and electrochemical properties of viologens in the molecular assemblies are discussed together with their potential applications as electron mediators for the electron donors, light-harvesting units and proteins. Contents
1 Introduction
2 Synthesis of viologens
2.1 Viologen organics
2.2 Poly(viologen) derivatives
3 Interfacial assembly of viologen-functinalized ultrathin films and aggregates
3.1 Langmuir-Blodgett films of amphiphilic viologens
3.2 Self-assembled monolayers of viologens
3.3 Layer-by-layer assembly of poly(viologen) derivatives
4 Conclusion and remarks