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. © The Royal Society of Chemistry 2016.