This talk will focus on the interactions of charged oligomers of the two structural types shown below with oppositely charged surfactants below and above the critical micelle concentration.  The presentation will cover both experimental studies and molecular dynamics simulations. In our studies we have found that remarkably different behavior occurs when surfactant is added to an oppositely charged oligomer of the two different series.  Oligomers having the charged groups only at the opposite ends of the molecule first undergo a blue shift of the absorption (compared to monomeric oligomer in solution) with a tail to the red.  A concurrent decrease and broadening of the fluorescence occurs as surfactant is added at ratios of surfactant to oligomer in the range 1:2 to 1:30.  As additional surfactant is added up to and beyond the critical micelle concentration the absorption and fluorescence shift back to very similar spectra such as are observed in aqueous and organic solutions.  In contrast, the OPE oligomers with charged groups on the middle ring undergo a red-shift in both absorption and fluorescence and there is usually a general increase in intensity of the latter.  Once again, as more surfactant is added to the solution towards and beyond the critical micelle concentration, the absorption and fluorescence spectra shift back to the original spectra. We attribute these spectral changes to the formation of two different aggregates or dimers in the presence of small amounts of surfactant.  For the end-only oligomers, all-atom molecular dynamics simulations of the interactions between the oligomers and surfactants in water suggest a face-to-face or �H� aggregate.  We attribute the red-shifted spectrum for the side-armed charged OPE to the formation of a �J� aggregate where the steric effect of the side-arms prohibits an �H� aggregated configuration.

Colloidal assembly of surfactant/oligomer complexes: Self-assembly, photophysics, and antimicrobial activity

247th National Meeting (2014)

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