Photoinduced Hydrogen Production with Artificial Photosynthesis System Based on Carotenoid−Chlorophyll Conjugated Micelles

To develop a photoinduced hydrogen production system based on an artificial photosynthesis model, the anionic water-soluble carotenoid dye crocetin, which has two carboxylate groups (a π electron conjugated polyene material with a carbon number of 20), electrostatically immobilized onto the surface of cationic surfactant cetyltrimethylammonium bromide (CTAB) micelles that included Mg chlorophyll- a and b (MgChl- a and b ) (Cro/MgChl), was prepared, and its photochemical properties were studied using UV−vis absorption and fluorescence spectroscopy. The fluorescence of MgChl- a and b was induced, with the excitation wavelength attributed to the absorption band of crocetin, indicating that a photoinduced energy transfer from the photoexcited state of crocetin to MgChl- a and b occurs via the CTAB micelle interface. The photostability of MgChl- a and b in Cro/MgChl was investigated under continuous visible irradiation. After 60 min of irradiation, the absorbance at 660 nm due to MgChl- a and b in Cro/MgChl and MgChl- a / b, which did not contain crocetin, decreased by 3.0% and 17%, respectively. Little photoinduced decomposition of the crocetin moiety of Cro/MgChl was observed. These results indicate that the photoinduced decomposition rate of MgChl- a / b in Cro/MgChl against irradiation was suppressed by the crocetin molecule on the surface of the micelles. An effective hydrogen production system in the presence of NADH as an electron donor, methylviologen (MV 2+ ) as an electron carrier, and platinum colloid as a hydrogen producing catalyst under visible light irradiation was developed using Cro/MgChl as a photosensitizer (3.6 μmol in 3 h), which was found to be better than using MgChl- a / b without crocetin (2.1 μmol in 3 h).