Inherent Chirality in Electrochemically Active Molecular Materials: Strategy and Panoramic Overview

The introduction of chirality in organic conjugated polymers has been considered for a wide variety of purposes and applications, i.e., in optics and sensoristics. In this frame, the possibility of coupling electroactivity and enantiorecognition capability is an ambitious objective of the modern chemical research. As commonly reported in literature, chirality in organic semiconductors has mostly been introduced by attaching chiral pendants to the electroactive conjugated backbone through suitable linkers; however, this approach usually leads to poor chirality manifestations. In our strategy, instead, chirality results from a tailored torsion internally produced along the conjugated backbone, and it is not due to the presence of any external stereogenic element. The general structure is here illustrated: the stereogenic core responsible for chirality interconnects two bithiophene pendants and the connectivity of the bi-heteroaromatic scaffold maintains the conjugation between the bithiophene termini. The symmetry of the monomer is C2, and the thiophene a–positions involved in the electrochemical polymerization are homotopic, so full regioregularity of the polymers is guaranteed. Several members of this innovative class of inherently chiral molecules have been designed, synthesized, characterized and submitted to electrochemical polymerization. Chirality is maintained even in the solid state, as proved by CD experiments carried out on polymer films. CD investigations performed under different polarization states revealed a tendency of the structure to flatten when the polymer is p-doped. This phenomenon is reversible and suggested the image of a breathing system. The electrochemical properties and the polymerization ability of a complete series of inherently chiral thiophene- and pyrrole-based monomers, both as racemates and as pure enantiomers, will be described and discussed.