The purification of water for human usage, agriculture, and industrial sectors is evolving into a leading global priority. Separation of ionic analytes across aqueous and organic phases using liquid-liquid extraction is an ideal strategy for high selectivity and large throughput volumes. However, it remains a challenge to selectively extract an ion at low concentration from a mixture of salts, such as, radioactive pertechnetate (TcO4–) generated in the nuclear fuel cycle. Furthermore, studies relating to the triggered release of these extracted anions in a different location, are still in their infancy. To this end, we describe a strategy for selective extraction of larger anions (TcO4–, PF6–) from a mixture containing smaller anions (Cl–) with corresponding light-triggered release. Cyanostar exhibits strong 2:1 complexation with large, weakly-coordinating anions like PF6–, which serves as a TcO4– surrogate allowing 19F NMR for quantitative evaluations. We also used cyanostar’s selectivity in extracting PF6– as a tetraethylammonium (TEA) salt from a salt mixture that contained a smaller anion, chloride (Cl–). Without the macrocycle, there was minimal partition of either salt (TEAPF6, TEACl) into the organic layer. With cyanostar present, size-selective partitioning of PF6– was observed, with complete transfer of the PF6– anion into dichloromethane at 2 equivalents of cyanostar. We harnessed cyanostars’ ability to photoisomerize under 365 nm UV light leading to a one-shot release of PF6– into an aqueous receiving phase. Irradiation with 365 nm light distorts the binding pocket to obliterate binding. Thus, natural partitioning of the salts drives the anion (PF6–) back to the aqueous phase. These findings highlight the potential for selective anion extraction and motivates exploration of new receptor classes to test selective binding and release of environmentally hazardous anions.

Extractive separation of larger anions driven by cyanostar macrocycle and corresponding photo-driven release

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