Inherently chiral conducting polymer film electrodes

In the last years we have been developing and characterizing \u201cspider-like\u201d oligothiophenes[1][2], to develop novel functional materials for energy and sensor applications, and to throw new light on the structure/reactivity relationships in the important class of oligothiophene semiconductors. When present, distortions from planarity (\u201cnodes\u201d) along the main conjugated chain impair the conjugation efficiency of the system, and lead to an increase in the HOMO-LUMO gap that limits the possible applications in the energetic field. However, the intrinsic 3D character of the nodes can also be advantageously exploited, as in the case of the purposedly non-planar multithiophene-based monomer TBTX (Figure 1)[3], displaying a 70\ub0 distortion around the central bond. Its intrinsically high ability for fast and regular electropolymerization allowed its use as a 3D promoter building block in copolymerizations, particularly with co-monomers endowed with key functional properties: a co-polymer, deposited by electropolymerisation of racemic TBTX together with a monomer bearing a crown-ether function (Figure 2), was found to outstandingly perform as the recognition element of a molecularly imprinted piezomicrogravimetric chemosensor for the determination of melamine, of high selectivity and sensibility, that has been patended and published[4][5]. Moreover, calculations revealed that the barrier to rotation around the central bond is very high, suggesting that TBTX exists as a pair of configurationally stable antipodes: thus, chirality is an inherent property of the whole molecule, which is devoid of carbon stereocentres. Actually TBTX enantiomers have been quantitatively and easily separated by chiral HPLC, and experiments of enantiomer TBTX electropolymerizations have been performed. The enantiopure specular conducting polymer films have been characterized together with the racemate one by CV, EIS, spectroelectrochemistry and circular dichroism with in-situ electrochemistry. Positive charge injection, reducing the torsion angle to achieve better \u3c0-system conjugation, results in a fully reversible "breathing" process of the 3D chiral conducting network upon potential cycling (Figure 3) The availability of materials able to couple electroactivity and enantiorecognition capability is an ambitious objective of the current chemical research, aiming to both electrically triggered enantioselective electron transfers and electrically monitored enantioselective recognitions. In this light, enantiorecognition tests on the enantiopure chiral polymer surfaces (particularly electrodeposited in ionic liquid on screen printed electrodes, to improve regularity and reproducibility) are in progress with interesting preliminary results [6]