Interaction of a new surface sensitive probe compound with anionic surfactants of varying hydrophobic chain length

Small aggregates of surfactant monomers start to form after addition of surfactant and coalesce at different critical aggregation constants until they reach the critical micellar concentration. Different sizes of the aggregates are believed to affect the binding of the probe molecules to the surface. [Display omitted] ► The added probe binds to the surface of the surfactant micelles. ► The equilibrium shifts between neutral and ionic forms of the probe on binding. ► Surfactant monomers are suggested to form small aggregates that coalesce to become bigger. The amide derivative of a bis-phenylethynyl compound meta linked to 2,6-pyridine (BPEAP) poses inherent equilibrium between its neutral and zwitterionic forms in the excited state. BPEAP has been found to bind to the surface of anionic micelles instead of penetrating inside. This phenomenon has been exploited to attempt controlling the process of equilibrium using sodium dodecyl sulfate (SDS) at its pre-micellar and near-micellar aggregation concentrations. The anionic surfactant has been found to alter the equilibrium between the said forms of BPEAP depending on its concentration in solution. The process has been further verified by using sodium decyl sulfate (SDeS), which has smaller hydrophobic chain length than SDS as also varies in the critical micellar concentration (CMC) and aggregation number. The binding constant of the probe to the surfactant aggregates varies depending on the extent of surface available to the fluorophore for attachment.