π-Extended dihydrophenazine based redox responsive polymers of intrinsic microporosity

Abstract

Redox-switchable Polymers of Intrinsic Microporosity (PIMs) are a promising yet underexplored class of materials. Here, we introduce π-extended dihydrophenazine-based PIMs for gas separation. The tert-butyl substituted Phen-PIM-1 stands out as a rare example of a redox-active switchable polymer with a high surface area (BET >600 m² g⁻¹) and excellent balance of porosity, pore size, and gas selectivity. Phen-PIM-1 is soluble in N-methyl pyrrolidone (NMP), enabling membrane fabrication, while the methyl-substituted Phen-PIM-2 is insoluble, highlighting the role of bulky tert-butyl groups (tBu) in solubility and film formation. Gas separation studies, performed on powder (IAST), demonstrate outstanding performance, with CO₂/N₂ selectivity up to 49. As a membrane material, Phen-PIM-1 shows competitive separation within the Robeson upper bound for several commercially important gas pairs, proving its potential for carbon capture and molecular sieving. Furthermore, these materials exhibit efficient and reversible redox switching upon chemical stimuli, leading to marked differences in properties and enhanced selectivity. This study establishes dihydrophenazine-based PIMs as a versatile platform for developing tunable, high-performance membranes for energy and environmental applications.