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Voltammetric responses of pentoxyresorufin in 4-(3-phenylpropyl)-pyridine (PPP) microdroplets immersed in aqueous electrolyte are investigated in the absence and in the presence of light. The reduction of pentoxyresorufin to leuco-pentoxyresorufin in the dark is shown to occur in a two-electron, two-proton process sensitive to the aqueous pH and the PPP vertical bar aqueous electrolyte interfacial tension. No significant net photoelectrochemical current responses are observed, although transient responses indicative of distinct electron and hole charge carriers are seen in the presence of pentoxyresorufin. EPR evidence confirms the formation of radical intermediates upon illumination. As a coreactant, duroquinone in the PPP microdroplet phase is investigated and also shown to undergo two-electron, two-proton reduction (to duroquinol) without significant photoelectrochemical activity. When investigated in combination, pentoxyresorufin acts as a photocatalyst for the oxidation of duroquinol to duroquinone. Wavelength-resolved photovoltammetry experiments clearly implicate pentoxyresorufin as the primary photoexcited intermediate. The :photoelectrochemical mechanism is explained on the basis of the presence of a long-lived (possibly charge-separated) photoexcited intermediate in the PPP microphase. Implications for light-energy harvesting are discussed.
Collins, A. M., Blanchard, G. J., Hawkett, J., Collison, D., & Marken, F. (2011). Liquid | Liquid | Electrode Triple-Phase Boundary Photovoltammetry of Pentoxyresorufin in 4-(3-Phenylpropyl)pyridine. Langmuir, 27(10), 6471-6477. https://doi.org/10.1021/la2010584