Viologens (1,1'-dialkyl-4,4'-bipyridiniums) gained significant attention when it was discovered that they possessed the ability to recognize one another through non-covalent, radical-radical interactions after reduction to the monoradical cation. Since this discovery, viologens have been used in a variety of applications due to their ease of synthesis and predictable redox and self-assembly processes. Recently, our group developed a new mechanism for the actuation of hydrogels using unimolecular polyviologens where the viologen subunits are linked by a hydrophilic spacer comprising oligoethylene glycol units. Once incorporated into a hydrogel network, the viologen subunits can be chemically or photochemically reduced to the monoradical cation, resulting in contraction of the hydrogel to 9% of its original volume. Here, we present our newly designed macrocrosslinker that consists of viologen units tethered by hydrophobic chains and end-capped with styrene functional groups. The sequence-defined polyviologen crosslinker was synthesized in an iterative process through addition of excess hexamethylene linker followed by addition of excess 4,4'-bipyridine, with precipitation steps in between. This new linker promotes a higher degree of intramolecular self-assembly due to the inherent hydrophobicity and therefore a faster actuation process. These gels can contract down to 15% of their original volume when exposed to blue light for 4 hours, even when only 0.15 mol% of the redox-responsive crosslinker is present. With a styrene functional handle, this sequence-defined polyviologen crosslinker can be incorporated into a wide range of materials.

Synthesis, self-assembly, and photomechanical gel actuator performance of a sequence-defined polyviologen crosslinker

2019 Fall National Meeting

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