Cross-Linked Supramolecular Polymer Gels Constructed from Discrete Multi-pillar[5]arene Metallacycles and Their Multiple Stimuli-Responsive Behavior

• Published in: Journal of the American Chemical Society 2014-06, Vol.136 (24), p.8577-8589
• Main Authors: Li, Zhong-Yu, Zhang, Yanyan, Zhang, Chang-Wei, Chen, Li-Jun, Wang, Chao, Tan, Hongwei, Yu, Yihua, Li, Xiaopeng, Yang, Hai-Bo
• Format: Article
• Language: English
• Subjects: Cross-Linking Reagents - chemical synthesis; Cross-Linking Reagents - chemistry; Gels - chemical synthesis; Gels - chemistry; Macromolecular Substances - chemical synthesis; Macromolecular Substances - chemistry; Molecular Structure; Organoplatinum Compounds - chemical synthesis; Organoplatinum Compounds - chemistry; Polymers - chemical synthesis; Polymers - chemistry; Quaternary Ammonium Compounds - chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja413047r

A new family of discrete hexakis-pillar[5]­arene metallacycles with different sizes have been successfully prepared via coordination-driven self-assembly, which presented very few successful examples of preparation of discrete multiple pillar­[n]­arene derivatives. These newly designed hexakis-pillar[5]­arene metallacycles were well characterized with one-dimensional (1-D) multinuclear NMR (1H and 31 P NMR), two-dimensional (2-D) 1H–1H COSY and NOESY, ESI-TOF-MS, elemental analysis, and PM6 semiempirical molecular orbital methods. Furthermore, the host–guest complexation of such hexakis-pillar[5]­arene hosts with a series of different neutral ditopic guests G1–6 were well investigated. Through host–guest interactions of hexakis-pillar[5]­arene metallacycles H2 or H3 with the neutral dinitrile guest G5, the cross-linked supramolecular polymers H2⊃(G5) 3 or H3⊃(G5) 3 were successfully constructed at the high-concentration region, respectively. Interestingly, these cross-linked supramolecular polymers transformed into the stable supramolecular gels upon increasing the concentrations to a relatively high level. More importantly, by taking advantage of the dynamic nature of metal–ligand bonds and host–guest interactions, the reversible multiple stimuli-responsive gel–sol phase transitions of such polymer gels were successfully realized under different stimuli, such as temperature, halide, and competitive guest, etc. The mechanism of such multiple stimuli-responsive processes was well illustrated by in situ multinuclear NMR investigation. This research not only provides a highly efficient approach to the preparation of discrete multiple pillar­[n]­arene derivatives but also presents a new family of multiple stimuli-responsive “smart” soft matters.