Polyanionic Cyclodextrin-Induced Supramolecular Assembly of a Cationic Tetraphenylethylene Derivative with Aggregation-Induced Emission

The combination of supramolecular chemistry and aggregation-induced emission-based luminogens (AIEgens) has recently attracted tremendous attention because of its ability to offer large emission enhancement even in substantially dilute solutions. In this work, a new aggregation-induced emission (AIE)-based supramolecular assembly has been reported, which consists of a polyanionic cyclodextrin derivative and a tetracationic tetraphenylethylene (TPE) derivative. Ionic cyclodextrins have attracted significant attention in host-guest supramolecular chemistry and pharmaceutical industry. However, ionic derivatives of beta-cyclodextrins have not been explored to establish noncovalent interactions-based aggregation assembly of the most popular class of AIEgens, i.e., tetraphenylethylene derivatives. The current report demonstrates AIE of a tetracationic methyl pyridinium derivative of tetraphenylethylene (TPy-TPE) induced by a polyanionic sulfated beta-cyclodextrin (S-beta CD). The AIE-based supramolecular assembly has been thoroughly investigated using steady-state fluorescence, ground-state absorbance, and time-resolved fluorescence measurements. Further, the response of the supramolecular assembly towards external stimuli, such as, ionic strength, pH, and temperature, has been investigated. In addition, the complexation behavior of the TPE derivative has also been compared with the native neutral beta-cyclodextrin derivative, which delineates the important role of the negatively charged portal of S-beta CD in inducing aggregation of the TPy-TPE. The stoichiometry of the complex has been found to be 3:1 for TPy-TPE:S-beta CD, using Job's plot analysis. Finally, to get insights into the underlying interactions between the supramolecular assembly components, molecular docking calculations have been performed.

Automated summary

The combination of supramolecular chemistry and aggregation-induced emission-based luminogens has attracted significant attention recently. In this study, a new supramolecular assembly based on aggregation-induced emission was reported, consisting of a polyanionic cyclodextrin derivative and a tetracationic tetraphenylethylene derivative. The assembly was thoroughly investigated using fluorescence, absorbance, and time-resolved fluorescence measurements, and its response to external stimuli was studied. The interaction between the assembly components was analyzed using molecular docking calculations.