Ferro-Self-Assembly: Magnetic and Electrochemical Adaptation of a Multiresponsive Zwitterionic Metalloamphiphile Showing a Shape-Hysteresis Effect

We report on a novel multi-stimuli-responsive amphiphile, 1-(Z)-heptenyl-1’-dimethylammonium-methyl-(3-sulfopropyl)ferrocene (6), whose self-assembly properties can be altered by three different stimuli, namely: (i) the addition of external salts which serve to unfold the sultone headgroup, thus triggering self-assembly of 6 into vesicles; (ii) oxidation to 6⁺, which changes the lipophilic ferrocene to a hydrophilic ferrocenium entity, thereby broadening the size-distribution of the aggregates; and (iii) exposition of 6⁺ to an external magnetic field of 0.8 T. Under thease conditions and at sufficient concentration, 6⁺ forms large, tubular aggregates with lengths of up to 15 µm, which persist for over 5 min after the field is switched off again. 6⁺ is thus the first amphiphile to exhibit a shape-hysteresis effect. The self-assembly/disassembly processes and their dynamics were studied live and in situ by optical birefringence measurements coupled to light scattering.