Photoinduced Electron Transfer on the Surfaces of Micelles

Abstract

Photoinduced electron transfer between N,N-dimethylaniline (DMA) and octadecylrhodamine B (ODRB) is studied on the surfaces of three alkyltrimethylammonium bromide micelles: dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromide (CTAB). The DMA and ODRB molecules are localized at the micelle surface. Time-resolved fluorescence and fluorescence yield data are presented and analyzed with the theoretical methods of ref 1. Lateral diffusion of the molecules over the micelle surfaces is included. Although the three micelles are structurally similar, pronounced differences in the electron-transfer kinetics are observed, with the overall amount of electron transfer increasing with alkyl chain length for the same DMA surface packing fraction. This result is attributed to differences in the solvent reorganization energy, possibly due to varying extents of water penetration into the headgroup regions of the three micelles. As the surfactant chain length increases, the solvent reorganization energy is reduced, resulting in faster electron transfer.

Solvent Reorganization Energy and Free Energy Change for Donor/Acceptor Electron Transfer at Micelle Surfaces: Theory and Experiment

“…Therefore, although treating λ and ∆G properly has a significant effect on the calculated distance-dependent electron-transfer rate, the weak dependence on size is insufficient to explain the data reported previously. 1 The data are discussed below in light of the new theoretical considerations. Figure 4B shows the rate coefficient vs distance for the final fits to the data using the 3-phase micelle model (see section IV).…”

“…For example, electron transfer from a donor to acceptors confined to move on the surface of spherical micelles has been studied theoretically and experimentally. 1,[14][15][16] The electron transfer dynamics are substantially modified by the restricted distribution of separations arising from the spherical geometry of the system, compared to those in a homogeneous liquid.…”

“…29 In addition to their important biological and industrial applications, micelles have long been of interest to the electron-transfer community. 1,9,16,[30][31][32][33][34][35][36] Despite this substantial attention, surprisingly little is known experimentally about the characteristics of micelles' surface regions.…”

Photoinduced Excited State Electron Transfer at Liquid/Liquid Interfaces

“…This includes scanning electrochemical microscopy (SECM), [15][16][17][18][19][20][21][22][23][24][25][26] thin-layer cyclic voltammetry, [27][28] and spectro-electrochemical methods (some utilizing recent advances in non-linear optics). [5][6][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] 3…”

Reactivity and Dynamics at Liquid Interfaces

“…These methods include scanning electrochemical microscopy (SECM), [552][553][554][555][556][557][558][559][560] thin-layer cyclic voltammetry 561,562 and spectro-electrochemical methods (some taking advantage of recent advances in non-linear optics). [563][564][565][566][567][568][569][570][571][572][573][574][575][576][577][578] In the SECM technique, one has the ability to widen the potential window and that increases significantly the range of the driving force (ΔG rxn ) for the ET reactions studied at the L/L interface. Because of that it has enabled the observation of the Marcus-inverted region (see below) and provided a reliable determination of the reorganization free energy.…”