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

Abstract

In coordination-based supramolecular materials such as metallogels, simultaneous temporal and spatial control of their assembly remains challenging. Here, we demonstrate that the combination of light with acids as stimuli allows for the spatiotemporal control over the architectures, mechanical properties, and shape of porous soft materials based on metal-organic polyhedra (MOPs). First, we show that the formation of a colloidal gel network from a preformed kinetically trapped MOP solution can be triggered upon addition of trifluoroacetic acid (TFA), and that acid concentration determines the reaction kinetics. As determined by time-resolved dynamic light scattering, UV-vis absorption and <sup>1</sup>H NMR spectroscopies and rheology measurements, the consequences of the increase in acid concentration are (i) an increase in the cross-linking between MOPs; (ii) a growth in the size of the colloidal particles forming the gel network; (iii) an increase in the density of the colloidal network; and (iv) a decrease in the ductility and stiffness of the resulting gel. We then demonstrate that irradiation of a dispersed photoacid generator, pyranine, allows the spatiotemporal control of the gel formation by locally triggering the self-assembly process. Using this methodology, we show that the gel can be patterned into a desired shape. Such precise positioning of the assembled structures, combined with the stable and permanent porosity of MOPs, could allow their integration into devices for applications such as sensing, separation, catalysis, or drug release.

Influence of the Surface Chemistry of Metal–Organic Polyhedra in Their Assembly into Ultrathin Films for Gas Separation

“…The acid treatment was selected because it has been previously employed with success to detach N-donor ligands from Rh-MOPs in solution. 24 The acid-treated films were characterized through UV adsorption spectra, water contact angle (WCA), and AFM to analyze the chemical and morphological changes induced by acid treatment.…”

Exploring the Interphase Structure of Poly(vinyl alcohol) during Sol–Gel Transition Using Selective Probes with Varied Molecular Sizes

“…As for sol−gel transition, techniques, i.e., rheological 25,26 and dynamic light scattering (DLS), 27,28 have been carried out to track such phase transition. The rheological measurement is normally used to determine the critical temperature for sol−gel transition based on the Winter criterion.…”

Control of Extrinsic Porosities in Linked Metal–Organic Polyhedra Gels by Imparting Coordination-Driven Self-Assembly with Electrostatic Repulsion

“…By controlling the coordination-driven self-assembly pathway of MOPs, recently we reported the successful fabrication of the linked MOP gels featuring hierarchical porous networks. 24,25 Instead of forming ordered frameworks like MOFs, the random crosslinking of MOPs as junctions with bisimidazole links results in the formation of colloids, followed by their further connections to form colloidal gels. In particular, we showed that the post-synthetic aging process induced the reorganization of crosslinked MOP networks inside the colloids and thus the control of extrinsic porosity.…”