The diverse chemical and biological functions of various anions and the adverse effects of others on our health and environment underscore the need for their detection, separation, and remediation with high precision and selectivity. Although the anion recognition field has attracted tremendous attention over the past two decades, vast majority of synthetic receptors still primarily rely on H-bonding and electrostatic interactions for binding guest anions and size- and shape-complementarity for selectivity. As a result, the prospect of differentiating anions on the basis of their intrinsic electronic properties, i.e., Lewis basicity and electron donating ability remained largely overlooked until anion–π-acid interaction surfaced in early-2000s. Adding a new paradigm to anion recognition chemistry, we discovered that in aprotic solvents where anions are less solvated and their electron donating ability follows their Lewis basicity trend, π-acidic receptors such as naphthalene and perylenediimides (NDI and PDI) were able to discriminate anions by engaging strong Lewis basic anions in formal electron transfer (ET) interaction, less Lewis basic anions in charge transfer (CT) interactions, and charge-diffuse anions in anion–π and CH/anion interactions. While anion-induced ET to π-acids (πA) leading to the formation of corresponding πA<sup>●– </sup>radical anions and πA<sup>2– </sup>dianions and anion/π-acid CT interactions exhibited distinct spectroscopic changes, presenting us with a novel multimodal anion sensing strategy, optically silent anion–π and CH/anion interactions allowed for the sequestration of charge-diffuse anions within NDI-based coordination polymers, metallacycles, and metal–organic frameworks. Furthermore, we recently designed and synthesized an NDI-based heteroditopic ion-pair receptor that simultaneously captured guest cation and anion in a cooperative fashion and released both ions when the guest cation was stripped away from the complex by a stronger chelating agent. Taken together, these revelations not only added a new dimension to anion recognition chemistry, but also exposed the sacrificial electron donating ability of Lewis basic anions. We exploited this unique electronic property of fluoride anion for electrode-free silver plating and luminescent silver nanoparticle synthesis, while others used it for light to electrical energy conversion in polymer solar cells.

Anion recognition with π-acids and Lewis acids

2019 Spring National Meeting

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