Alkali base triggered intramolecular charge transfer metallogels based on symmetrical A–π–D-chiral-D–π–A type ligands

Abstract

Three L-tartaric acid based symmetrical A–π–D-chiral-D–π–A type structural isomeric nitrobenzylidenes (1–3) have been synthesized with intent to achieve isomer specific metallogels with intramolecular charge transfer properties. Alkali metal ions in these systems not only trigger charge transfer but also play a vital role in gelation. The presence of intramolecular rather than intermolecular charge transfer as well as aggregation has been well established by various kinds of experiments using UV-vis, CD, ¹H NMR, DFT and crystallography techniques. The role of alkali metal ions in triggering ICT was proved by titration with their respective crown ethers. Notably, Na⁺ afforded twisted fiber morphology whilst Li⁺ gave merely long range fibers. The true gel phase material was proved by detailed rheological studies.