Influence of three anionic gemini surfactants with different chain lengths on the optical properties of a cationic polyfluorene.

The effects of three sulfonate gemini surfactants with different hydrophobic chain lengths (8, 10, and 12 carbon atoms) on the optical properties of a fluorene-based conjugated cationic polymer poly{[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]-fluorene-phenylene} bromide (PFP) dissolved in DMSO-water solutions (4% v/v) or water were investigated, respectively. When surfactants with PFP dissolved in DMSO-water solutions (4% v/v) are incubated, a decrease in photoluminescence (PL) intensity and a red shift of emission maxima are obtained at low surfactant concentrations. Intriguingly, two different Stern-Volmer constants (KSV1 and KSV2) are obtained and analyzed in detail for the first time. Further increase in the surfactant concentration enhanced PL intensity, and distinct blue shifts of both absorption and emission maxima are observed. Importantly, the turning point between the emission quenching and enhancement is closely related to the hydrophobic chain length: the longer the chain length, the earlier the turning point appears. Simulation studies provide strong evidence to explain these phenomena. Surface tension measurements show more insight on the interactions between PFP and surfactant. On the contrary, no emission quenching is obtained at low surfactant concentrations for PFP dissolved in water.