Photophysical and Photochemical Properties of Pyranine/Methyl Viologen Complexes in Solution and in Supramolecular Aggregates:  A Switchable Complex

The properties of a novel complex between pyranine (a photoacid and an electron donor species) and methyl viologen (an efficient electron acceptor, MV+2) in aqueous and in micellar solutions were determined. On the basis of the electrostatic driven force for pyranine/methyl viologen (pyranine/MV2+) complexation, the distribution of the complexant species could be manipulated using ionic micellar aggregates. This distribution permits control over competitive photochemical and photophysical pathways and therefore allowed maximization of electron- and proton-transfer capabilities. Pyranine/MV2+ complexes (for the acid and conjugated base pyranine species) were characterized by UV−Vis and fluorescence titrations. Pyranine/MV2+ photoredox reactions were investigated by monitoring the transients (laser flash photolysis) due to the solvated electron, the reduced (PO-•) and oxidized (PO+•) forms of pyranine, and the semireduced methyl viologen (MV+•). Ionic aqueous micelles (sodium dodecyl sulfate and cetyltrimethylammonium chloride) and anionic reversed micelles (sodium bis(2-ethylhexyl)sulfosuccinate) were used to disassemble the complex by attraction of one of its species by an oppositely charged micellar aggregate. Present findings demonstrate the formation of a complex and its manipulation, which may allow the development of a photocatalyst agent whose properties can be adjusted by the appropriate disposition of the complex partners in supramolecular aggregates.