Supramolecular gels show great potential as soft smart materials, since their gel-sol phase transitions can be triggered by external stimuli. In this context, we prepared a series of dual-pH responsive and highly fluorescent DMSO gels by functionalizing aggregation-induced emission (AIE) active fluorophores with guanidiniocarbonyl pyrrole carboxylate (GCP) zwitterionic binding sites (see Fig. 1). In the gel state an intense fluorescence emission is observed, as the gelator molecules are fixed within a dense network of self-assembled fibres held together by H-bond assisted ion pairs between the GCP zwitterions. The phase transition to the sol state can be triggered by various stimuli (acid or base, temperature and mechanical stress) and goes along with a loss of fluorescence due to an increasing motional freedom of the monomers.

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​Figure 1: (A) Molecular structure of a bis-zwitterionic AIE-active gelator based on aromatic thioethers reported by Voskuhl and coworkers and dimerization of the zwitterionic binding site. (B) Schematic representation of the gelation process. (C) AFM image of the self-assembled fibrillar network. (D) Increase of emission intensity upon increasing concentrations. (E) DMSO gel under daylight and UV-light, and gel-sol transition triggered by the addition of acid and base.

As a next step we designed a modular construction kit for the preparation of more sophisticated supramolecular copolymers and multicomponent gels. In this project we several central core units (with useful properties, e.g. fluorescence, E/Z-isomerizability, water solubility) will be combined via orthogonal switchable supramolecular binding motifs (GCP zwitterions, metal-ligand binding sites, host-guest systems).

Recent Publication

M. Externbrink, S. Riebe, C. Schmuck, J. Voskuhl, Soft Matter 2018, 14, 6166-6170: “A Dual pH-Responsive Supramolecular Gelator with Aggregation-Induced Emission Properties”.