Cross-linked AIE supramolecular polymer gels with multiple stimuli-responsive behaviours constructed by hierarchical self-assembly

Herein, we present the successful construction of a new family of cross-linked AIE supramolecular polymer gels with multiple stimuli-responsive behaviours through hierarchical self-assembly involving coordination and host-guest interactions. Firstly, by decorating the tetraphenylethylene (TPE) core with two dipyridyl moieties and two pillar[5]arene units, a new dipyridyl donor H1 was successfully prepared. Then, a rhomboidal metallacycle H2 with four pillar[5]arene units and a hexagonal metallacycle H3 with six pillar[5]arene units were constructed through coordination-driven self-assembly. Subsequently, cross-linked supramolecular polymers H2⊃G₂ and H3⊃G₃ were formed through host-guest interactions. The obtained supramolecular polymers were able to transform into supramolecular polymer gels under higher concentration, which displayed AIE properties due to the restriction of TPE intramolecular motions within three-dimensional polymeric networks. More interestingly, by taking advantages of dynamic nature of both coordination bonds and host-guest interactions, the resultant supramolecular polymer gels displayed multiple stimuli-responsive gel-sol transitions under different stimuli, such as temperature, competitive guest molecules, halides, etc., along with the "on-off" of fluorescence.