Ionic self-assembly of pillar[5]arenes: proton-conductive liquid crystals and aqueous nanoobjects with encapsulation properties

Liquid crystal (LC) pillar[n]arenes have been barely explored due to their time-consuming and complicated synthesis, despite their promising properties for metal-ion separation, drug delivery, or surface functionalization. Herein, we report an easy and reliable method to functionalize pillar[n]arene macrocycles through electrostatic interactions. These ionic materials were prepared by ionically functionalizing a pillar[n]arene containing ten amine terminal groups with six different carboxylic acids. This supramolecular approach results in ionic pillar[n]arenes which self-organize into LC phases with good proton-conducting properties. Moreover, ionic functionalization provides a new amphiphilic character to the pillar[n]arenes, which self-assemble in water to produce a variety of nanoobjects (i.e., spherical or cylindrical micelles, vesicles, solid nanospheres, or nanotubes) that are capable of encapsulating a model hydrophobic drug. Interestingly, the presence of coumarin moieties in the chemical structure of the ionic pillar[n]arenes results in self-organized materials with light-responsive properties due to the ability of coumarins to undergo photo-induced [2+2] cycloaddition. In particular, we demonstrate that coumarin pohotodimerization can be employed to fabricate mechanically stable proton-conductive LC materials, as well as to obtain photo-responsive nanocarriers with light-induced release of encapsulated molecules. An easy and fast method to functionalize pillararenes through ionic bonds to obtain interesting materials for their encapsulation properties and proton conduction.

Automated summary

This article presents an easy and reliable method to functionalize pillar[n]arene macrocycles through electrostatic interactions. The resulting ionic pillar[n]arenes self-organize into liquid crystal phases with good proton-conducting properties and exhibit interesting encapsulation properties. Moreover, the presence of coumarin moieties in the chemical structure allows for light-responsive properties and photo-induced release of encapsulated molecules.