Remarkable Reinforcement of a Supramolecular Gel Constructed by Heteroditopic [18]Crown-6-Based Molecular Recognition

Abstract

The heteroditopic crown ether-based ligand 1 containing the diazafluorenylimino group as a binding site for the Zn2+ and Cs+ was synthesized. The ligand 1 can be gelated in DMSO/water with and without Cs+ in the presence of the Zn2+ ion. Interestingly, the remarkable gelation reinforcement of gel 1 occurred with Cs+ in the presence of Zn2+, which is due to the formation of a sandwich complex. According to DFT calculations, one Zn2+ is bound to two diazafluorenylimino moieties in a tetrahedral structure. In addition, one Cs+ ion is bound to two crown-rings. The Zn2+-diazafluorenylimino ligand gel without Cs+ shows a spherical structure with 250800nm diameter, whereas the Zn2+-diazafluorenylimino-based ligand gel with Cs+ shows a fiber structure with 6070nm diameter and several micrometers of lengths. The rheological properties of the Zn2+- diazafluorenylimino-based ligand gel were strongly dependent on the presence of Cs+.