Fine‐Tuning the Spring‐Like Motion of an Anion‐Based Triple Helicate by Tetraalkylammonium Guests

Abstract

Supramolecular springs are a class of molecular devices that may provide implications to the macroscopic spring behavior from the molecular level. Helical structures are suitable molecular springs because the specific twisting of the helical strands can cause spring‐like (extension‐contraction) movement along the axis upon external stimuli. Herein we report an anion‐based triple‐helicate spring, which can undergo reversible contraction–extension motion through introduction and removal of tetraalkylammonium cations, including TMA+ and analogous irregular tetrahedral cations bearing different alkyl chains, while the relative orientation of the two phosphate ions changes to facilitate guest inclusion. Notably, the degree of contraction (shortening of the helical pitch) can be fine‐tuned by varying the shape and size of guest cation. However, with the larger cations (TEA+, TPA+ and TBA+), the meso‐helicate configuration is obtained, which interconverts with the helicate by addition/removal of TMA+ ion.

Hierarchical Self‐Assembly of Adhesive and Conductive Gels with Anion‐Coordinated Triple Helicate Junctions

“…The PO 4 3À •••PO 4 3À distance is 14.8 Å, which is slightly longer than those in a phosphate triple helix reported by our group. [18] Due to the limited cavity of H Me , the encapsulation of a guest was not observed. The TMA + counter-cations were found to be distributed around the triple-helical [(PO 4 ) 2 (L Me ) 3 ] 6À assemblies.…”