Electrostatic loading and photoredox-based release of molecular cargo from oligoviologen-crosslinked microparticles

Controlling electronic coupling between multiple redox sites is of interest for tuning the electronic properties of molecules and materials. While classic mixed-valence (MV) systems are highly tunable, e.g., via the organic bridges connecting the redox sites, metal-bridged MV systems are difficult to control because the electronics of the metal cannot usually be altered independently of redox-active moieties embedded in its ligands. Herein, this limitation was overcome by varying the donor strengths of ancillary ligands in a series of cobalt complexes without directly perturbing the electronics of viologen-like redox sites bridged by the cobalt ions. The cobaltoviologens [1 X -Co] n+ feature four 4-X-pyridyl donor groups (X = CO 2 Me, Cl, H, Me, OMe, NMe 2 ) that provide gradual electronic tuning of the bridging Co II centers, while a related complex [2-Co] n+ with NHC donors supports exclusively Co III states even upon reduction of the viologen units. Electrochemistry and IVCT band analysis indicate that the MV states of these complexes have electronic structures ranging from fully localized ([2-Co] 4+ ; Robin−Day Class I) to fully delocalized ([1 CO2Me -Co] 3+ ; Class III) descriptions, demonstrating unprecedented control over electronic coupling without changing the identity of the redox sites or bridging metal. Additionally, single-crystal XRD characterization of the homovalent complexes [1 H -Co] 2+ and [1 H -Zn] 2+ revealed radical-pairing interactions between the viologen ligands of adjacent complexes, representing a type of through-space electronic coupling commonly observed for organic viologen radicals but never before seen in metalloviologens. The extended solid-state packing of these complexes produces 3D networks of radical π-stacking interactions that impart unexpected mechanical flexibility to these crystals.

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Electrostatic loading and photoredox-based release of molecular cargo from oligoviologen-crosslinked microparticles

Abstract: Although on-demand cargo release has been demonstrated in a wide range of microparticle platforms, many existing methods lack specific loading interactions and/or undergo permanent damage to the microparticle to release...

Cited by 2 publications

References 36 publications

Electrostatic loading and photoredox-accelerated release of antibiotics from oligoviologen-crosslinked hydrogels using red light

Electrostatic loading and photoredox-accelerated release of antibiotics from oligoviologen-crosslinked hydrogels using red light

Controlling Intramolecular and Intermolecular Electronic Coupling of Radical Ligands in a Series of Cobaltoviologen Complexes

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