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A Ru-Re supramolecular complex photocatalyst (Fig. 1) was used to measure the quantum yield of a carbon dioxide reduction reaction. The sample was irradiated with 17 × 10^-9 einstein·s^-1 of 470 nm light and then the absorption spectrum and number of photons absorbed were measured. Carbon monoxide generated from the reduction reaction was then quantified using a gas chromatograph. The graph in Fig. 2 correlating the quantity of carbon monoxide generated to the number of photons absorbed was obtained. Since the reaction quantum yield corresponds to the slope in Fig. 2, a result of 40 % was obtained for the given experiment.

Fig. 1 Diagram of Ru-Re Supramolecular Complex
Photocatalyst Reaction

Fig. 2 Quantity of Carbon Monoxide Generated vs.
Number of Photons Absorbed

An attempt was made to directly observe intermediates during the carbon dioxide photoreduction reaction of a Ru-Re supramolecular complex photocatalyst (Fig. 1). Time-course changes in absorption spectra measured during the photocatalytic reaction are shown in Fig. 3. Difference spectra with respect to the absorption spectrum measured at the start of measurement are shown in Fig. 4. The new absorption observed near 550 nm in Fig. 3 and Fig. 4 is due to the absorption spectra of intermediates. A comparison to previously reported data confirmed that the intermediates are one-electron reduced species from a photoelectron-transfer reaction of the Ru-Re supramolecular complex photocatalyst.

Fig. 3 Ru-Re Supramolecular Complex Photocatalyst Reaction Spectral Measurement Results

Fig. 4 Ru-Re Supramolecular Complex Photocatalyst Reaction Difference Spectra Calculation Results