Multiple-electron-transfer reactions are highly pertinent to solar energy storage through CO2 reduction and water splitting, and in some of the most efficient dye-sensitized solar cells (DSSCs), which utilize the two-electron-transfer I-/I3- redox shuttle. If multiple-electron-transfer oxidations could be directly coupled to dye regeneration in dye-sensitized energy-conversion schemes, less overpotential would be required for the reactions and therefore, the usable solar spectrum could be expanded and an increased efficiency gained. Our group recently demonstrated that model catalyst compounds co-anchored to a mesoporous dye-sensitized TiO2 thin film could be oxidized twice through visible-light excitation of the molecular dyes, requiring self-exchange electron transfer. However, we wanted to determine whether this charge accumulation could be increased from two to three, or even four. Therefore, we synthesized a series of meso-substituted porphyrins containing carboxylic acid acceptor groups (n = 1, 2, 3, 4) and triarylamine donor groups (m = 4 – n) that could each be oxidized to the overall oxidation states of 1+, 2+, 3+, or 4+ (using a metallated porphyrin). Spectroelectrochemical measurements were performed and the data used to calculate their redox potentials and self-exchange electron diffusion coefficients. The porphyrins were then used in place of the model catalyst compounds and studied by transient absorption spectroscopy. The results from this work will be presented.

Studies of self-exchange electron transfer and charge accumulation at sensitized TiO2 for multiple-electron-transfer chemistry using a series of amine-functionalized porphyrins

251st National Meeting (2016)

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