Electron-Responsive Supramolecular Soft-materials

Electron-Responsive Supramolecular Soft-materials Involving Viologen-Based Metamorphic Tectons

This PhD project aims at developing a rational approach towards electron or photo-responsive supramolecular soft-materials (gels, liquid crystals). Priority will be given to supramolecular gels capable of achieving reversible sol/gel transitions in response to either direct or indirect (light-induced) electron transfer. The basic concepts and the targeted molecular tectons that will be developed to address this challenge will build on recent achievements of the hosting laboratory in the field of molecular metamorphism based on the p-dimerization of viologen-based radicals as the driving force of reorganizations (Scheme 2).^8–11

Scheme 2.

In terms of molecular design, the targeted works will meet two challenges: i) devising easy to make molecular viologen-based building blocks capable of self-assembling in solution to yield dynamic 3D- supramolecular network-forming gels and ii) achieving a redox/photochemical control over the assembly-disassembly process to allow a remote triggering of the collapse and revival of the network (sol«gel) under application of electrical/photochemical stimuli.

All the strategies that will be explored to ensure the formation of self-assembled gelled networks will rely on a suitable/reasoned functionalization of the bipyridium core (R in Scheme 2). It includes the introduction of organic ligands enabling the formation of coordination polymers, or the incorporation of low molecular weight gelators promoting the establishment of structuring orthogonal supramolecular interactions (H bonds, π-π...) within the assemblies.^5–7

The association/dissociation of these networks will be actuated upon changing the redox state of bipyridinium units involved in the tectons from their dicationic state to their radical cation state, the driving force of the process being the non-covalent and fully reversible dimerization occurring between bipyridinium cation radicals (scheme 2).^8–11  Different approaches will be considered to promote the dissociation of the network  through formation of isolated π-dimerized species at the reduced state, it includes the introduction of suitable covalent linkers between each units involved in the dimerization^8–10 or the use of cavitand-shaped hosts selected for their ability to stabilize such dimers.¹¹