Electronic energy levels in lyotropic chromonic liquid crystals formed by ionic perylene diimide derivatives

Abstract

Lyotropic Chromonic Liquid Crystals (LCLCs) represent dispersions of disk-like organic molecules in water that form columnar aggregates bound together by weak hydrophobic interactions and aligned parallel to each other. Dry films of LCLCs preserve the aggregated molecular packing and orientational order. Our idea is that this class of materials is ideally suited for flexible electronics applications since their structure is shaped by relatively weak non-covalent molecular interactions. We report an experimental study that aims to elucidate the influence of ionic substitutes on the energy band of LCLCs based on perylene-diimide derivatives. Using cyclic voltammetry and light absorption techniques, we explore the role of functionalization of several materials of this class with ionic end groups (positive and negative) on the molecular LUMO/HOMO energy level positions. We find that both positively and negatively charged LCLC molecules show decrease in energy positions in comparison with chemically-similar non-mesogenic materials. The experimentally estimated parameters show the deep-lying LUMO energy levels (below −4.0 eV) for all studied LCLC materials with ionic substitutes.