Hierarchical self-assembly of an amphiphilic tris-urea in aqueous media is shown. A mixture of the amphiphilic tris-urea and an alkaline solution gave a viscous solution composed of fibrous aggregates. This viscous solution transformed into supramolecular hydrogels, which are capable of hierarchically organizing into higher-order aggregates in response to several cationic triggers. The resulting supramolecular hydrogels were relatively stiff and their storage moduli attained over 10(3) Pa. The stimuli-responsive and optical properties of the resulting hydrogels were influenced by the cationic trigger. Proton and calcium ion triggers gave pH- and chemical stimuli-responsive hydrogels, respectively. A terbium ion trigger also provided a highly luminescent hydrogel through energy transfer from the tris-urea to terbium.
Keywords: energy transfer; gels; lanthanides; self-assembly; supramolecular polymers; ureas.
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