Electrochemistry of 3-D, inherently chiral thiophene-based monomers

The availability of materials which could couple electroactivity and enantiorecognition capability is an ambitious objective of the modern chemical research. So far chirality in organic semiconductors has mostly been introduced by attaching chiral pendants to the electroactive conjugated backbone through suitable linkers; however, this approach usually results in modest chirality manifestations. We have planned to make a revolution to this strategy by preparing polymerizable chiral oligothiophene monomers in which chirality results from a tailored torsion internally produced in the oligothiophene backbone (inherently chiral monomers) so that the whole monomer, and the resulting polymer films, are 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 also requires that the polymerization sites of the monomers be homotopic, thus granting the perfect constitutional regularity of the polymers. Moreover, all 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 [1]; 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.