Multi‐Stimuli‐Responsive Organometallic Gels Based on Ferrocene‐Linked Poly(Aryl Ether) Dendrons: Reversible Redox Switching and Pb²⁺‐Ion Sensing

Abstract

We describe the design, synthesis, and "stimuli-responsive" study of ferrocene-linked Fréchet-type [poly(aryl ether)]-dendron-based organometallic gels, in which the ferrocene moiety is attached to the dendron framework through an acyl hydrazone linkage. The low-molecular-weight gelators (LMWGs) form robust gels in both polar and non-polar solvent/solvent mixtures. The organometallic gels undergo stimuli-responsive behavior through 1) thermal, 2) chemical, and 3) electrochemical methods. Among them, conditions 1 and 3 lead to seamlessly reversible with repeated cycles of identical efficiency. Results indicate that the flexible nature of the poly(aryl ether) dendron framework plays a key role in retaining the reversible electrochemical behavior of ferrocene moiety in the LMWGs. Further, the organometallic gelators have exhibited unique selectivity towards Pb(2+) ions (detection limit ≈10(-8) M). The metal ion-sensing results in a gel-sol phase transition associated with a color change visible to the naked eye. Most importantly, decomplexing the metal ion from the system leads to the regeneration of the initial gel morphology, indicating the restoring ability of the organometallic gel. The metal-ligand binding nature has been analyzed by using (1)H NMR spectroscopy, mass spectrometry, and DFT calculations.

Poly(aryl ether) Dendrons with Monopyrrolotetrathiafulvalene Unit‐Based Organogels exhibiting Gel‐Induced Enhanced Emission (GIEE)

“…The dendron in the gel phase were initially examined by using optical microscopic techniques 18. 35 The optical microscope images of the gels of 1 a and 1 b obtained from the mixture of DMSO/water with and without thermal treatment were depicted in Figure 3.…”

“…31 The mechanism of phase transition is identical to that observed during electrochemical oxidation, that is, TTF was oxidized to TTF . + , which results in the repulsion between the MPTTF units to destroy the π–π and S ⋅⋅⋅ S interactions between TTF units, and thereby the gel network collapses 18. Notably, when an equivalent ascorbic acid (Vitamin C, Vc) dissolved in small amount of water was added to the oxidized solution, which was able to reduce TTF .…”

Multi-Stimuli-Responsive Polymer Materials: Particles, Films, and Bulk Gels

“…Reversible sol–gel phase transition could be realized under thermal and electrochemical stimuli. Moreover, these gels showed a specific response to Pb 2+ ions triggering the gel–sol transition, paving the way to an easy detection kit for lead ions with a detection limit close to the ppb level 322. Most recently, Su et al fabricated a multi‐stimuli‐responsive photochromic metal–organic gel responsive to light, heat, water, and anions (Figure b).…”

Janus Dendrimer from Poly(Aryl Ether) Linked PAMAM for Supergelation and Guest Release

“…Previous results from our group revealed that poly(aryl ether) dendrons linked to pyrene, naphthalene, anthracene, ferrocene, phenothiazine through an acylhydrazone linkage readily form organogels. In order to develop hydrogels based on poly (aryl ether) dendrons, we have attached water soluble PAMAM dendrons with poly(aryl ether) acylhydrazone.…”