Photophysics of water soluble perylene diimides in surfactant solutions

Our previous photophysical study of water soluble perylene diimides (WS-PDIs) has suggested that WS-PDIs are present in aqueous solution in partially aggregated form (Tang, T. J.; Qu, J. Q.; Müllen, K.; Webber, S. E. Langmuir 2006, 22, 7610-7616) In this article we present a study of the effect of surfactants (dodecyltrimethylammonium chloride (DTAC), sodium dodecyl sulfate (SDS)) on the photophysics of WS-PDIs. Adding surfactant to WS-PDI solutions is accompanied by their increased fluorescence quantum yield and lifetime and a more structured absorption spectra. We are able to demonstrate that above the surfactant critical micelle concentration (cmc) the WS-PDI moieties are molecularly dispersed and isolated from each other. Our findings are consistent with the existence of weakly interacting aggregates of WS-PDIs in pure water, which can be broken up by surfactants even below the cmc, although we cannot rule out that the observed photophysical changes arise from modifying the local environment of molecularly solubilized WS-PDIs (e.g., local polarity or modification of the molecular planarity).