Electrochemistry of inherently chiral thiophene-based monomers

The usual approach to the introduction of chirality in organic semiconductors is to attach chiral pendants to the electroactive conjugated backbone through suitable linkers, or to perform polymerization in an asymmetric medium; however, this approach usually results in modest chirality manifestations. We now propose polymerizable chiral oligothiophene monomers in which chirality results from a tailored torsion internally produced in the oligothiophene backbone so that the whole monomer, and the resulting polymer films, are chiral ("inherently chiral"). To achieve this goal we are introducing into the monomer structure different typologies of stereogenic elements which do not interrupt the conjugated sequence. The structural design of the monomers is also conceived so that the polymerization sites of the monomers be homotopic, thus granting a perfect constitutional regularity of the polymers. Moreover, the substrates are conceived so as to envisage the possibility of a large scale production, starting from inexpensive, commercially available reagents. We will present and discuss in detail the electrochemical properties and polymerization ability of the first three inherently chiral monomers developed within this project, both as racemates and as separated enantiomers. The first one has recently performed outstandingly, even as a racemate, as a 3D promoter building block in copolymerizations with co-monomers endowed with key functional properties but scarce attitude to polymerization, affording the development of an oustandingly performing melamine sensor; the corresponding separated enantiopure monomers fully retain the high attitude to fast and regular polymerization; moreover, the resulting polymer films fully retain the dissimmetry of enantiopure monomers, well evidenced by solid-state dichroism measurements.