A Neutral Porous Organic Polymer Host for the Recognition of Anionic Dyes in Water

Neutral hosts for the recognition of anionic guests in water remain underdeveloped due to the inherent thermodynamic barrier for desolvation. As a new strategy to address this challenge, we have repurposed crosslinked porous organic polymers (POPs) as hosts. This polymer architecture affords a hydrophobic environment with a densely packed array of urea hydrogen bond donors to cooperatively promote anion desolvation and recognition in water. As a proof-of-concept, we demonstrate through adsorption assays that the resulting Urea-POP-1 can discriminate between structurally different dyes containing phosphonate, sulfonate, and carboxylate anions. Moreover, when compared to Methyl-POP-1, a control POP lacking hydrogen bond donors, we find that recognition is not exclusively driven by the hydrophobicity of the dyes but through selective hydrogen bonding interactions of the urea sidechains with the anionic functional groups. This starting point sets the stage to exploit the modularity of our design to build a family of neutral polymer hosts with tunable pore sizes and anion preferences for fundamental investigations and targeted applications.