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

We describe the design, synthesis, and "stimuli-responsive" study of ferrocene-linked Fr�chet-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 Pb2+ 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 1H NMR spectroscopy, mass spectrometry, and DFT calculations. Receptive dendritic gelators: Ferrocene-containing poly(aryl ether) dendron based low-molecular-weight organometallic gels exhibit multi-stimuli-responsive behavior under thermal, chemical, and electrochemical conditions, and in also presence of Pb2+ ions. Results suggest the reversible thermal and redox switching of the gel, in addition to its ability to sense Pb2+ ions with restorable tendency (see figure). � 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.