Supramolecular oligourethane gel as a highly selective fluorescent “on–off–on” sensor for ions

Stimuli-responsive supramolecular gels (SRSGs) are an important class of smart materials. It is of practical importance to develop an SRSG which can both detect and remove toxic metal ions. We have designed and synthesized an aggregation induced emission (AIE)-active oligourethane (OU) gelator which self-assembles into a supramolecular gel (OUG), through hydrogen-bonding, π–π stacking and van der Waals interactions. By taking advantage of the weak and dynamic nature of these non-covalent bonds, OUG shows stimuli-response to multiple factors. Importantly, OUG has the capacity for real-time detection and high selectivity for Fe3+, HSO4− and F−. The lowest detection limits are in the range of 5.89 × 10−9 to 8.17 × 10−8 M, indicating high sensitivity. More importantly, OUG is shown to adsorb and separate Fe3+ from aqueous solution, with an absorbing rate of up 97.5%. A simple writing board was fabricated, which could be written repeatedly and reused. OUG acts as a reversible and recyclable “on–off–on” fluorescence sensor via competitive cation–π and cation–anion interactions. OUG has great potential as an environmentally sustainable probe for ions.