Aggregation behaviour of a water-soluble ammonium-functionalizedpolythiophene: Luminescence enhancement induced by bile-acid anions

The water-soluble poly{trimethyl-[7-(3-thienylsulfanyl)heptyl]ammonium iodide-co-thiophene} (PTNDMe3) forms aggregates whose size span a large range of values, depending on solvent, concentrationand film formation conditions. Larger aggregates were detected by atomic force microscopy and dynamic light scattering, smaller ones by DOSY NMR, UVevisible and fluorescence. All techniques indicate a reduced aggregation of PTNDMe3 in DMSO relative to water and a marked de-aggregation of PTNDMe3 in water following addition of bile-acid anions such as deoxycholate and ursodeoxycholate.The latter effect shows itself through a very large enhancement of the polymer photoluminescence likely caused by disruption of aggregated non-emissive exciton traps. A tailored combination of electrostaticand hydrophobic interactions between the polymer and the bile-acid anions seems to be necessary to achieve this effect. These observations suggest that this polythiophene might provide a basis for the development of fluorescent sensors suitable for the detection of medium-sized amphiphilic biomolecules.