Inclusion of Two Push−Pull N Methylpyridinium Salts in Anionic Surfactant Solutions: A Comprehensive Photophysical Investigation

Two N-methylpyridinium salts with push −pullproperties have been investigated in the aqueous solution ofanionic micelles of sodium dodecyl sulfate (SDS) and potassiump-(octyloxy)benzenesulfonate (pOoBSK) surfactants. Thesemolecules are known to be extremely sensitive to the localenvironment, with their absorption spectrum being subjected to anet negative solvatochromism. These compounds are alsocharacterized by an excited state deactivation strictly dependenton the physical properties of the chemical surrounding, with the formation of intramolecular charge-transfer (ICT) statesaccordingly stabilized. Thanks to steady-state and femtosecond resolved spectroscopic techniques, the photophysical propertiesof these molecules in the presence of anionic micelles have been fully characterized and an efficient permeation within themicellar aggregates can thus be inferred. The extent of the changes in the photophysical properties of these molecules (withrespect to what is observed in water) is an indicator of the medium experienced in the nanoheterogeneous solutions: enhancedfluorescence emissions, reduced Stokes shifts and slowed-down excited state decays strongly confirm the confinement within ascarcely polar and restraining environment. The slightly different behavior shown in the two types of micelles can be ascribed to apeculiar interaction between the aromatic moiety of the surfactant and that of the cations. Additionally, the inclusion promotesthe solubilization of these poorly water-soluble salts, which is alluring in their promising use as DNA binders for antitumorpurposes. Thus, the anionic micelles allowed the solubilization of the pyridinium salts under investigation, which in turn allowedthe characterization of the nonhomogeneous medium established by the micellar aggregates.