Construction of Metallacage‐Cored Supramolecular Gel by Hierarchical Self‐Assembly of Metal Coordination and Pillar[5]arene‐Based Host−Guest Recognition

Abstract

In this work, a Pd2L4 metallacage 2•([BF4]−)4 with four pillar[5]arene units is first prepared and characterized by 1D multinuclear NMR (1H, 11B, and 19F NMR), 2D 1H−1H correlation spectra, 1H−13C heteronuclear single quantum coherence, and diffusion‐ordered NMR spectroscopy, and electrospray ionization time‐of‐flight mass spectrometry. By the introduction of a ditopic guest molecule 3 into a chloroform solution of 2•([BF4]−)4, a supramolecular polymer network gel is successfully constructed based on the metal coordination interactions and host−guest recognition between the pillar[5]arene units of 2•([BF4]−)4 and neutral ditopic guest molecule 3. The temperature and pH responsivenesses of the supramolecular gel are studied, which are further employed for the controlled release of different cargos. As a demonstration, emodin and methylene blue are trapped in the cavities of the metallacage and in the pores of the supramolecular gel, respectively. Methylene blue is first released along with the gel–sol transition while emodin is then released by the further addition of acid to destroy the metallacage. This study explores the use of metallacage‐cored supramolecular network gels for sequential controlled release and contributes to the development of smart and adaptive materials.

Spatiotemporal Control of Supramolecular Polymerization and Gelation of Metal–Organic Polyhedra

“…24,25 Recent advances with MOPs have allowed porosity to be incorporated as a new property in the soft materials or to form extended crystalline structures such as metal−organic frameworks (MOFs). 26−28 MOPs, as building blocks, can be assembled into metallogels via a wide variety of intermolecular interactions such as electrostatic attraction, 29,30 dynamiccovalent bonds, 31 coordination bonds, 32,33 or host−guest complexation, 34,35 which can all be triggered in response to various stimuli. However, it is still a challenge to spatiotemporally control the reaction pathway, structures, and resulting properties of metallogels.…”

High compression strength single network hydrogels with pillar[5]arene junction points

“…They are relatively easy to synthesize, and the selective introduction of functional groups in targeted position is less complicated as compared to the most other macrocyclic hosts. [38][39][40][41] Poly(2-isopropenyl-2-oxazoline) (PiPOx) has recently emerged as a versatile and functional platform for the preparation of thermoresponsive copolymers with tunable lower critical solution temperature (LCST) behavior, hydrogels, molecular brushes and materials for photonics. [42][43][44][45][46][47][48] Furthermore, PiPOx can be prepared with well-defined characteristics, is highly hydrophilic, biocompatible 49 and it can be easily modified by post-polymerization reactions with carboxylic acids.…”

Recent Advances on Stimuli‐Responsive Smart Materials and their Applications

“…The host/guest interaction well studied by addition of dyes like methylene blue and emodin. The methylene blue promotes gel to sol conversion after release from the metallacage whereas release of emodin depends on addition of acid which protonate the pyridine ‘N′ favour dissociation of emodin from metallacage …”