Multifunctional redox-tuned viologen-based covalent organic polymers

The immobilization of molecular switches within materials can give rise to new bulk properties that are useful for a variety of applications. Here, we report the synthesis and characterization of covalent organic polymers composed of cyclotriphosphazene core moieties linked together by redox-switchable viologen units. The polymers are isolated as non-porous, micro- and nano-sized spherical particles whose constituent viologens allow access to three distinct redox states: dicationic, radical-cationic and neutral. With viologens in their dicationic state, the particles were used for magic printing, gaseous ammonia sensing, and efficient oxoanion capture. With viologens in any oxidation state, the polymers were capable of capturing 200 to 380% of their weight of iodine vapor. Iodine capture within all of the viologen-based polymers was fast, requiring minutes, as compared to capture by previously reported polymers, which requires hours. With viologens in their neutral state, the polymers exhibited the highest iodine loadings reported to date. Upon one and two-electron reduction, the polymers partially or completely lost their cationic character and, concomitantly, their anion removal capability.