**1. Introduction**

Considerable effort has been devoted to the development of sophisticated and functional molecular machine architectures [1–4]. An integral part of this endeavour has focused on constructing simple molecular switches that mimic elegant examples found in nature [5–7] and expanding the scope of their functional remit to new applications [8–12]. This includes the field of anion recognition chemistry, with systems being applied in the detection and extraction of environmentally damaging and biologically important ions [13–16]. Switchable systems associated with anion recognition have focused mainly on anion-mediated events, where a coordination event induces a detectable change in the molecule which can be sensed by a reporter group [17–20]. However, the field is beginning to expand to include systems where the binding itself can be controlled by external stimuli.

We have previously reported examples of pH-dependent anion receptors which promote chloride efflux under acidic conditions [21–23]. Switchable transporters may allow the movement of anions in healthy cells to be regulated, akin to the mechanism found in many transport proteins [7,24], or find use in targeting cancer cells for efflux induced apoptosis [25,26]. Additionally, a small number of compounds has been developed in which anion binding can be controlled by a photophysical input [27,28]. Photoisomerization can be used to alter the shape of the binding cleft, resulting in a difference in binding affinity between the two states [29,30]. The application of switches governed by electrochemical stimuli provides another method through which anions can be bound and released, ye<sup>t</sup> these systems remain underexplored.

The hydroquinone/quinone redox couple is found extensively throughout biology [31,32], and its well-defined electrochemical properties highlighted its potential candidacy for use in a switchable receptor system [33–35]. With this in mind, we designed a simple ye<sup>t</sup> novel receptor scaffold consisting of a hydroquinone motif with an appended benzamide group. It was envisaged that the convergen<sup>t</sup> hydrogen bonds of the amide and one of the hydroquinone OH group could create a chloride recognition site inspired by similar benzenediol receptors [36]. Subsequent oxidation to the corresponding quinone would induce a rotation around the quinone-benzamide bond due to the favorable formation of an intramolecular hydrogen bond, which is demonstrated in Figure 1. The oxidation event removes the OH groups and causes a conformational change in the orientation of the amide NH and would therefore greatly diminish the chloride affinity of the oxidised form of the receptor.

**Figure 1.** Proposed binding mode of the hydroquinone (left) and proposed intramolecular hydrogen bonded quinone species (right).

A series of hydroquinone-benzamide receptors appended with a variety of electron withdrawing and donating groups was prepared. Subsequently, these molecules were oxidised to afford their quinone forms. Chloride binding affinity has been determined, and the results compared to evaluate the effect of the redox-activated conformational switch on chloride recognition. Additionally, cyclic voltammetry has been used to study the electrochemical properties of the receptors.
