Highly enantioselective electrodes based on inherently chiral organic conducting films

An attractive objective in materials research is to develop materials coupling electroactivity with enantiorecognition capability. However, the usual strategy adopted to this aim, hinging on attaching chiral pendants to an electroactive polyconjugated backbone, generally results in modest chirality manifestations. We have thus designed electroactive chiral polyheterocycles, where chirality is not external to the electroactive backbone, but inherent to it, resulting from a tailored torsion produced by the periodical presence of atropisomeric, conjugatively active biheteroaromatic scaffolds. This affords enantiopure electroactive films of impressive chiroptical activity; moreover, since the stereogenic element coincides with the electroactive site, chirality manifestations can be finely and reversibly tuned by the electric potential, since progressive injection of positive charges forces the atropisomeric scaffold angle to regularly decrease to favour delocalization. Such deformations are elastic and reversible, as revealed by CD spectroelectrochemistry, which suggested us the image of a "breathing chirality". To test the enantiorecognition ability of the new inherently chiral conducting films we have in the last months developed an efficient protocol in ionic liquid medium affording preparation of very reproducible electrode surfaces by electrooxidation of the enantiopure monomers on screen printed electrode supports. The resulting specular R and S electrodes have been tested in the presence of (R)-(+)- and S-(-)-N,N-dimethyl-1-ferrocenylethylamine specular probes. The response is highly and reproducibly enantioselective (with even more than 100 mV separation between R and S probes, either with single enantiomers and with the racemate), specular for R vs S surfaces with respect to S and R probes, and reversible in repeated alternating sequences of S and R probe sensing on a single electrode. [1] The same behaviour is obtained starting with monomers significantly different from the chemical point of view, but structurally designed according to the same rationale, proving the general validity of our new concept.