Pyrene-sensitized electron transport across vesicle bilayers: dependence of transport efficiency on pyrene substituents

Abstract

Endoergic electron transport across vesicle bilayers from ascorbate (Asc⁻) in the inner waterpool to methylviologen (MV²⁺) in the outer aqueous solution was driven by the irradiation of pyrene derivatives embedded in the vesicle bilayers. The initial rate of MV²⁺ reduction is dependent on the substituent group of the pyrenyl ring; a hydrophilic functional group linked with the pyrenyl ring by a short methylene chain acts as a sensitizer for the electron transport. Mechanistic studies using (1-pyrenyl)alkanoic acids (1a–c) as sensitizers suggest that the electron transport is mainly initiated by the reductive quenching of the singlet excited state of the pyrene by Asc⁻ and proceeds by a mechanism involving electron exchange between the pyrenes located at the inner and outer interface across the vesicle bilayer. We designed and synthesized novel unsymmetrically substituted pyrenes having both a hydrophilic group linked by a short methylene chain and a hydrophobic long alkyl group (5a–c), which acted as excellent sensitizers for the electron transport across vesicle bilayers.