Fluorescence lifetime imaging microscopy (FLIM) reveals
vesicle
sizes, structures, microenvironments, reagent partitioning, and system
evolution with two chemical reactions for widely used surfactant–water
systems under conditions relevant to organic synthesis, including
during steps of Negishi cross-coupling reactions. In contrast to previous
investigations, the present experiments characterize surfactant systems
with representative organohalide substrates at high concentrations
(0.5 M) that are reflective of the preparative-scale organic reactions
performed and reported in water. In the presence of representative
organic substrates, 2-iodoethylbenzene and 2-bromo-6-methoxypyridine,
micelles swell into emulsion droplets that are up to 20 μm in
diameter, which is 3–4 orders of magnitude larger than previously
measured in the absence of an organic substrate (5–200 nm).
The partitioning of reagents in these systems is imaged through FLIMdemonstrated
here with nonpolar, amphiphilic, organic, basic, and oxidative-addition
reactive compounds, a reactive zinc metal powder, and a palladium
catalyst. FLIM characterizes the chemical species and/or provides
microenvironment information inside micelles and vesicles. These data
show that surfactants cause surfactant-dictated microenvironments
inside smaller micelles (<200 nm) but that addition of a representative
organic substrate produces internal microenvironments dictated primarily
by the substrate rather than by the surfactant, concurrent with swelling.
Addition of a palladium catalyst causes the internal environments
to differ between vesiclesinformation that is not available
through nor predicted from prior analytical techniques. Together,
these data provide immediately actionable information for revising
reaction models of surfactant–water systems that underpin the
development of sustainable organic chemistry in water.