Electrochromic Graphene Molecules

Abstract

Polyclic aromatic hydrocarbons also called Graphene Molecules (GMs), with chemical composition C₁₃₂H₃₆(COOH)₂ were synthesized <i>in situ</i> on the surface of transparent nanocrystalline indium tin oxide (<i>nc</i>-ITO) electrodes and their electronic structure was studied electrochemically and spectro-electrochemically. Variations in the potential applied onto the <i>nc</i>-ITO/GM electrodes induce only small changes in the observed current, but they produce dramatic changes in the absorption of the GMs, which are associated with their oxidation and reduction. Analysis of the absorption changes using a modified Nernst equation is used to determine standard potentials associated with the individual charge transfer processes. For the GMs prepared here, these were found to be <i>E</i>_1,ox⁰ = 0.77 ± 0.01 V and <i>E</i>_2,ox⁰ = 1.24 ± 0.02 V <i>vs</i> NHE for the first and second oxidation and <i>E</i>_1,red⁰ = −1.50 ± 0.04 V for the first reduction. The charge transfer processes are found to be nonideal. The nonideality factors associated with the oxidation and reduction processes are attributed to strong interactions between the GM redox centers. Under the conditions of potential cycling, GMs show rapid (seconds) color change with high contrast and stability. An electrochromic application is demonstrated wherein the GMs are used as the optically active component