Exploiting stable radical states for multifunctional properties in triarylamine-based porous organic polymers

Redox-active porous organic polymers (POPs) have enormous potential in applications ranging from electrocatalysis to solar energy conversion. Exploiting the different electronic states offers exciting prospects for controlling host-guest chemistry, however, this aspect of multifunctionality has to date, remained largely unexplored. Here, we present a strategy for the development of multifunctional materials with industrially sought-after properties. A series of hydrophobic POPs containing redox-active triarylamines linked by ethynyl (POP-1), 1,4-diethynylphenyl (POP-2) and 4,4′- diethynylbiphenyl (POP-3) bridges have been synthesised and characterised by NMR and EPR spectroscopy, as well as spectroelectrochemistry and computational modelling. The facile electrochemical or chemical oxidation of the POPs generate mixed-valence radical cation states with markedly enhanced adsorption properties relative to their neutral analogues, including a 3-fold improvement in the H2 uptake at 77 K and 1 bar, and an increase in the isosteric heat of adsorption for CO2.