Hydrophobic Acceleration of Electron Transfer Processes.

Electron transfer processes between 1-alpha-naphthyl-3-oxa-alkanes (1-n, n = 1, 8, 12, 16) and 2-alkyl-3,5,6-trichloro-1,4-benzoquinones (2-n, n = 8, 12, 16) facilitated by hydrophobic-lipophilic interactions (HLI) have been investigated by means of fluorescence spectroscopy in dioxane-H(2)O systems of different psi values, where psi is the volume fraction of the organic component of an aquiorgano mixture. Three lines of evidence, namely, EPR, UV-vis, and fluorescence quenching, indicate that electron transfer between 1-12 and 2-12 has occurred. Furthermore, both UV-vis evidence and the near constancy of the life time tau of 1-12() in the presence of different concentrations of the quencher 2-12 show that the electron transfer is preceded by preassociation, i.e., the quenching process is static. Therefore, the extent of HLI-driven coaggregation (preassociation) between the donors and the acceptors may be assessed from the Stern-Volmer slopes (Ksv). The chain-length effect, and possibly also a chain-foldability effect, has been observed. A notable observation is the importance of solvent aggregating power (SAgP) effect, which is indicated by the surge of Ksv values at psi </= 0.40 (dioxane-H(2)O) for monomeric 1-12.