Artificial photosynthesis is potentially a green economic approach for converting sunlight into practical energy. Herein, we report on photo energy conversion into ionic current via solar energy induced endergonic proton transfer across a polymeric membrane. Water soluble, pyrenol photoacid dye molecules (Fig. 1a) allow for light absorption and proton generation. Spectrophotometric titration curves indicated that the unbound dye in solution had a hydroxyl pKa value of 5.8. The photoluminescence measurements indicated that the hydroxyl excited-state pKa value, pKa*, was -0.7. Hence, the maximum attainable photovoltage from proton pumps utilizing the dye was estimated to be ~380 mV (59 mV x ΔpKa). The initial model system comprised of conical nanopore poly(ethylene terephthalate) scaffolds asymmetrically functionalized with dye molecules. The bound dyes provided a basis for a cationic region adjacent to an unmodified carboxylate region. The tailored regions of fixed charges was intended to mimic a solid-state semiconductor pn-junction and be used to separate photogenerated ions. Electrochemical and absorption spectroscopy measurements (Fig. 1b) of the bound dye to PET indicated a decrease in the pKa value to 5.0, was attached via two out of three ammonium groups, and had a binding density of 0.3 dyes/nm2. Two-photon fluorescence microscopy of modified films further verified that the dye was covalently attached to the film where it still functioned as a photoacid. Under visible-light illumination and a -100 mV reverse bias, excitation of these photo-acid-sensitized nanopore scaffolds resulted in an ionic photocurrent. This work provides an experimental and theoretical baseline for future work for photovoltaic materials as ion exchange membranes in solar fuel devices.

Visible light-driven proton pumps utilizing photoacid molecules and polymeric nanopore scaffolds

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.