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

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 250-800 nm diameter, whereas the Zn²⁺-diazafluorenylimino-based ligand gel with Cs⁺ shows a fiber structure with 60-70 nm diameter and several micrometers of lengths. The rheological properties of the Zn²⁺- diazafluorenylimino-based ligand gel were strongly dependent on the presence of Cs⁺. [ABSTRACT FROM AUTHOR]