Fig. 3. Optimizing formation and decay of the radical anion Py˙^2– by an anionic micelle. (a) Drawn-to-scale pictures of the relevant zones of an SDS micelle (gray, core, radius 19.6 Å; white, Stern layer, diameter 6.8 Å)32 in water (blue) and calculated molecular sizes, illustrating the most probable locations of the reaction partners and intermediates. The light-harvesting complex is attached to the boundary of the micelle core,33,34 and (top) in its excited form ³[Ru(bpy)₃]²⁺ the ligand protruding farthest into the Stern layer has been turned into a radical anion.27 The high dipole moment31 of the redox catalyst Py^– helps overcome the Coulombic repulsion and enables Py^– to enter the Stern layer in the orientation shown in the upper drawing, such that it can acquire sufficient orbital overlap with ³[Ru(bpy)₃]²⁺ to undergo the Dexter energy transfer25 EnT. The sacrificial donor Asc^2– (top), as well as the delocalized radical anion Py˙^2– and the hydrated electron e˙–aq (bottom), can only reside in the aqueous phase. These properties ensure the unhindered sequence of reactions EnT and ET while strongly suppressing the undesired reactions Q, R, and S₁ (compare, Fig. 2b and Table 1). (b) Main plot, concentration traces of the electron precursor Py˙^2– in deoxygenated homogeneous aqueous solution (brown) and 30 mM aqueous SDS (red) in the photolysis of 6 × 10^–5 M [Ru(bpy)₃]²⁺, 3 × 10^–4 M Py^– and 1.5 mM Asc^2– at pH 12.7 with a single green pulse, intensity given above the traces. The increased yield and much longer life of Py˙^2– in the micellar environment are obvious. Inset, transient absorption spectra (top, [Ru(bpy)₃]⁺, gray in water, dark gray in SDS; bottom, Py˙^2–, same color coding as in the main plot) at 10 μs after the laser flash and separated by the procedure described in ESI-3.5,† demonstrating the practically exclusive presence of [Ru(bpy)₃]⁺ in homogeneous solution and that of Py˙^2– in the micellar system. Further information, see text.