Photoredox Processes in the Aggregation and Gelation of Electron-Responsive Supramolecular Polymers Based on Viologen

Abstract

Viologen-based ditopic bis-pyridinyl-triazole bidentate ligands self-assemble in the presence of palladium ions into supramolecular polymers whose structure is imposed by the directed formation of coordination bonds. Light-irradiation of these electron-responsive supramolecular materials triggers a photo-induced electron transfer yielding isolated π-radicals and dimers of radicals. The photoreduction events and the associated dimerization steps trigger a large-scale reorganization occurring within the supramolecular network yielding aggregates or gels depending on the irradiation conditions (power, duration). Detailed electrochemical, spectro-electrochemical and photochemical analyses were conducted to understand the mechanisms at stakes in these light-induced aggregation and gelation.

Supramolecular polymers: Recent advances based on the types of underlying interactions

“…For instance, symmetrical systems, where both ends of the hinge were functionalized with terpyridine or bipyridine-like ligands, were reported as supporting metallopolymers in combination with a source of Zn 2+ , Fe 2+ or Pd 2+ cations. [185][186][187][188][189] Photo/redox stimulation of certain of the resulting 1D coordination polymers in solution was found to trigger large scale reorganization along with a macroscopic sol/gel-type phase transition. [186,190] Also, photo-or electrically responsive metallosupramolecular polymers were fabricated and used to build multiswitchable molecular logic gates.…”

Chiral and conductive viologen-based supramolecular gels exhibiting tunable charge-transfer properties

“…38–40 These self-assemblies have, for instance, been used to produce self-erasing or thermochromic inks. 41,42 Viologen-based LMWGs have also been obtained by introducing various self-assembling functions promoting metal–ligand bonds, 28–30 H-bonds, 43 Coulombic forces 44 or van der Waals interactions. 45…”

“…27 We have focused in recent years on the development of supramolecular gels built from LMWGs incorporating 4,4 0bipyridinium units. [28][29][30] These planar dicationic p-conjugated acceptors, better known as viologens (V 2+ ), offer many advantages for developing conductive gels and hybrid materials. 31 In addition to providing two mobile counter anions, they can potentially participate in electron transport through two successive one-electron reductions yielding stable radical cations (V + ) and quinoid neutral species (V 0 ).…”

“…[38][39][40] These self-assemblies have, for instance, been used to produce self-erasing or thermochromic inks. 41,42 Viologen-based LMWGs have also been obtained by introducing various self-assembling functions promoting metal-ligand bonds, [28][29][30] H-bonds, 43 Coulombic forces 44 or van der Waals interactions. 45 The ability of the cholesteryl substituted viologen derivative 1 2+ (Scheme 1) studied in the present article to form gels was first reported by Lu and coworkers.…”

Chiral and Conductive Viologen-based Supramolecular Gels Exhibiting Tunable Charge-Transfer Properties

“…27 We have focused in recent years on the development of supramolecular gels built from LMWGs incorporating 4,4'-bipyridinium units. [28][29][30] These planar dicationic π-conjugated acceptors, better known as viologens (V 2+ ), offer many advantages for developing conductive gels and hybrid materials. 31 In addition to providing two mobile counter anions, they can potentially participate in electron transport through two successive one-electron reductions yielding stable radical cations (V +• ) and dianions (V 0 ).…”