Bifunctional Nanoscale Assemblies: Multistate Electrochromics Coupled with Charge Trapping and Release

Abstract

We demonstrate controlled charge trapping and release, accompanied by multiple color changes in a metallo-organic bilayer. The dual functionality of the metallo-organic materials provides fundamental insight into the metal-mediated electron transport pathways. The electrochemical processes are visualized by distinct, four color-to-color transitions: red, transparent, orange, and brown. The bilayer is composed of two elements: 1) a nanoscale gate consisting of a layer of well-defined polypyridyl ruthenium complexes bound to a flexible transparent electrode, and 2) a charge storage layer consisting of isostructural iron complexes attached to the surface of the gate. This gate mediates or blocks electron transport in response to an applied voltage. The charge storage and release depend on the oxidation state of the layer of ruthenium complexes (=gate). Combining electrochemistry with optical data revealed mechanistic information: the brown coloration of the bilayer directly relates to the formation of intermediate ruthenium species, providing evidence for catalytic positive charge release mediated through the gate.

Keywords: charge storage; electrochemistry; electrochromism; metallo-organics; thin films.