Insights into the self-assembly of cationic pi-conjugated polymers-DNA hybrid structures

Water-soluble -conjugated polymers (CPs) have been recently designed as good candidates for developing aqueous optical sensing systems, because their optical response are very sensitive conformation and supramolecular assembly.1 In this frame, the design of different conjugated polyelectrolytes has attracted much interest, in particular cationic polythiophenes (PT),2 as thiophene-based polymers represent a versatile, central class of -conjugated polymers for organic electronics. Indeed, the regioregularity and the nature of the PT substituents are crucial to tune the optoelectronic properties and processability, and different types of ionic groups or side chains have been tested to achieve solubility in aqueous solution.

Here we present our recent studies on the design and self-assembly of a series of cationic polythiophenes in interaction with various specific DNA. By means of (chir)optical spectroscopy we observe that the PT/DNA supramolecular complexes present a remarkable induced circular dichroism signal in the achiral PT absorption region, which is indicative of the conformational effect induced by the binding to DNA. The influence of the PT side groups, DNA sequence and topology (single-stranded vs double-stranded), and composition, are studied in order to establish the structure-properties relationships and to give insights into the self-assembly mechanisms. Importantly, we have observed that DNA sequence-specific interactions are at play upon self-assembly with CPE, with ICD signatures that relate to the right- or left-handed conformational chirality of polymer backbone within the supramolecular duplexes. These results indicate the possibility of using these cationic polymers for designing hybrid structures with specific functional nucleic acids, such as G-quadruplex structures, aptamers, etc. in order to evolve towards specific optical (bio)sensors.