RAdically RespoNsive Metal-Organic Supramolecular GELs – ANGEL

ANGEL aims at developing a rational approach towards supramolecular metallogels capable of achieving reversible sol/gel transitions in response to electrical stimuli. Such responsiveness remains almost unexplored, despite being essential to ensure implementation of such materials in devices.
The barriers to be lifted to reach such challenging objective are both scientific and technologic. At a fundamental level, the concepts proposed in ANGEL rely on the use of easy to make and highly versatile redox-responsive building blocks whose reversible association/dissociation can be triggered by application of a low electrical voltage. From a technical point of view ANGEL aims at developing dedicated tools allowing to carry out in situ analyses of the gel phase and to identify the chemical and physical mechanisms responsible for the redox-triggered sol-gel transitions.
From a molecular point of view, the targeted amorphous 3D cross-linked networks forming gels will be obtained through spontaneous self-assembly of tailor-made and easy to make low molecular weight building blocks driven by the formation of orthogonal, thermodynamically stable, and kinetically labile intermolecular bonds. it includes binding of selected metal ions with multitopic organic ligands yielding coordination polymers and the formation of host-stabilized supramolecular charge transfer complexes between selected pi-conjugated organic donors and viologen-based acceptors. The structure and properties of the network leading to gelation will be anticipated through a careful design/choice of the pi-conjugated units, of the ligands and of the metal ions. Triggering gel/sol transitions with electrons will be achieved through a reversible/selective redox control over the building/collapse of the network. Dissociation of the cross-linked gel state to produce a mixture of non-interacting, discrete molecular objects in aqueous solution, and vice versa, will be achieved in ANGEL upon exploiting the unique electrochemical and chemical properties of dicationic 4,4’-bipyridinium units used as key building and redox-responsive elements. The electron-triggered self-assembly or dissociation of the building elements will rely on the ability of 4,4’-bipyridiniums to form very different, albeit very stable, supramolecular complexes in their oxidized or reduced states.