Modulating the Emission Intensity of Poly-(9,9-bis(6‘-N,N,N-trimethylammonium)hexyl)-Fluorene Phenylene) Bromide Through Interaction with Sodium Alkylsulfonate Surfactants

The interaction between the cationic HTMA-PFP (Poly-(9,9-bis(6‘-N,N,N-trimethylammonium)hexyl-fluorene phenylene) bromide) and oppositely charged sodium n-alkyl sulfonate surfactants of different chain lengths has been studied in DMSO−water solutions (4% v/v) by UV−visible absorption, fluorescence spectroscopy, fluorescence lifetimes, electrical conductivity, and 1H NMR spectroscopy. Polymer−surfactant interactions lead to complex spectroscopic behaviors which depends on surfactant concentration. At low surfactant concentrations, the observed strong static fluorescence quenching of fluorescence seems to be associated with formation of aggregates between polymer chains neutralized through interaction with surfactants. This is supported by conductivity and by analysis of absorption spectra deconvoluted at each surfactant concentration using an adapted iterative method. In contrast, above the surfactant critical micelle concentration, there is a strong fluorescence enhancement, leading in some cases to higher intensities than in the absence of surfactants. This is attributed to the transformation of the initially formed aggregates into some new aggregate species involving surfactant and polymer. These changes in HTMA-PFP fluorescence as a function of n-alkyl sulfonate concentration are important for the general understanding of polymer−surfactant interactions, and the aggregates formed may be important as novel systems for applications of these conjugated polyelectrolytes.