Photophysics of pyrene-end-capped poly(ethyleneoxide) in aqueous micellar environments

Abstract

The photophysical behavior of pyrene-end-capped poly(ethyleneoxide) (PYPY) has been studied in different aqueous micellar environments like cetyltrimethylammonium bromide (CTAB, cationic), triton X-100 (TX-100, non-ionic) and sodium dodecyl sulfate (SDS, anionic). In pure aqueous medium, the polymer solution shows dual emission corresponding to the monomer and the excimer. The relative intensity of the monomer and the excimer emissions shows interesting variation with the addition of the surfactants leading to the determination of the critical micellar concentrations (CMCs) of the micelles. The determined CMCs for CTAB and TX-100 micelles are in good agreement with the existing literature values. In SDS, however, variation of different fluorometric parameters against surfactant concentration results in the CMC values noticeably different from the reported CMC values for SDS micelles. This has been attributed to the interaction between SDS and the poly(ethyleneoxide) (PEO) chain of the polymer leading to the formation of mixed micelles. The micropolarity around the fluorophore has been determined in the micellar environments from a comparison of the variation of the relative fluorescence intensities of the monomer to the excimer band in water-dioxane mixtures with varying composition.