SOLVENT REORGANIZATION ENERGY AND FREE-ENERGY CHANGE FOR DONOR ACCEPTOR ELECTRON-TRANSFER AT MICELLE SURFACES - THEORY AND EXPERIMENT/

Theories are presented for calculating the solvent reorganization ener gy and the free energy change which occur in photoinduced donor/accept or electron transfer at the surface of micelles. The theories are base d on the Marcus theory for spherical reactants in a dielectric continu um. The micelle is modeled with regions of differing dielectric proper ties, representing the micelle core, the headgroup region, and the sur rounding water. The free energy change accompanying electron transfer can be calculated from redox measurements made in bulk liquids. The th eories are applied to previously published photoinduced intermolecular electron-transfer data between octadecylrhodamine B (ODRB) and N,N-di methylaniline (DMA) molecules.(1) The ODRB and DMA molecules are locat ed in the surface region of three different types of surfactant micell es: dodecyl-, tetradecyl-, and cetyl-trimethylammonium bromide (DTAB, TTAB, and CTAB, respectively). The data show an increased rate of elec tron transfer with increasing micelle radius. Application of the new t heory to the electron-transfer data along with information provided by neutron scattering experiments show that the headgroup regions of the three micelles have different dielectric constants because water pene tration into the headgroup regions decreases as the surfactant length increases.