The objective of this lecture is to report recent development of artificial photosynthesis for production of hydrogen using solar energy. High quantum yields and long-lived charge separation, which mimic the multi-step electron-transfer processes in the photosynthetic reaction center, have been achieved by electron donor-acceptor ensembles linked by covalent bonding.1 During the multi-step electron-transfer processes, however, a significant amount of energy is lost to attain the final long-lived charge-separated state. Then, simple electron donor-acceptor dyads linked by covalent or non-covalent bonding have been developed to attain a long-lived and high-energy charge-separated state without significant loss of excitation energy.2 More sophisticated supramolecular complexes composed of light harvesting and charge-separation units have been constructed by using non-covalent bonding such as p-p interaction, coordination bonds, and hydrogen bonds to attain long-lived charge-separated states with a high light harvesting efficiency.3-5 Recent development of photocatalytic hydrogen production using artificial photosynthetic systems is also reported together with hydrogen storage by fixation of CO2 with H2 as a form of formic acid (HCOOH) that can be converted selectively back to H2 in the presence of an appropriate transition metal complex catalyst.6 Combination of photocatalytic hydrogen generation with the catalytic CO2 fixation with H2 and the decomposition of HCOOH back to H2 provides excellent systems for cutting CO2 emission.
(1) Imahori, H.; Guldi, D. M.; Tamaki, K.; Yoshida, Y.; Luo, C.; Sakata, Y.; Fukuzumi, S. J. Am. Chem. Soc. 2001, 123, 6617.
(2) Fukuzumi, S. Phys. Chem. Chem. Phys. 2008, 10, 2283.
(3) Fukuzumi, S.; Kojima. T. J. Mater. Chem. 2008, 18, 1427.
(4) Kojima, T.; Honda, T, Ohkubo, K.; Shiro, M.; Kusukawa, T.; Fukuda, T.; Kobayashi, N.; Fukuzumi, S. Angew. Chem., Int. Ed. 2008, 47, 6712.
(5) Fukuzumi, S.; Honda, T.; Ohkubo, K.; Kojima, T. Dalton Trans. 2009, 3880.
(6) Fukuzumi, S. Eur. J. Inorg. Chem. 2008, 1351