Fluorescent nanoassemblies between tetraphenylethenes and sulfonatocalixarenes: a systematic study of calixarene-induced aggregation

In recent years, various stimulus-responsive nanoarchitectures have been fabricated by virtue of the calixarene-induced aggregation (CIA) strategy by our group and others, displaying functional applications of controlled release and catalysis. Herein, we aimed to demonstrate a systematic study of CIA that how and to what extent the structures of hosts and guests affect the assembly behavior. Tetraphenylethene (TPE) analogues were employed as model substrates due to their feature of aggregation-induced emission, which converts aggregation to easily observable fluorescence signals. As a result, the complexation-induced aggregation of TPE guests by macrocyclic hosts was conveniently monitored by fluorescence spectroscopy. Three typical macrocyclic hosts, cyclodextrins, cucurbiturils and p-sulfonatocalixarenes, were engaged in the complexation-induced aggregation of TPE guests. The obtained results show that the preorganized cyclic scaffold and the cavity binding capability of p-sulfonatocalixarenes play a crucial role in CIA performance, besides the well-accepted charge compensation. To generalize the feature of CIA, we further studied the complexation-induced aggregation of TPE guests by heparin, a model polyanion that forms polyion complex micelles with cationic substrates. The similarities and differences between CIA assemblies and polyion complex micelles were claimed.