Artificial Light-Harvesting Model in a Self-Assembly Composed of Cationic Dyes and Inorganic Nanosheet

This paper proposes an efficient artificial light-harvesting system in a host–guest assembly composed of functional dyes and inorganic nanosheet. Although we have already reported an efficient energy transfer between two types of porphyrin molecules on inorganic nanosheets (e.g., J. Am. Chem. Soc. 2011, 133, 14280), the number of photons captured by one acceptor molecule (photon-harvesting efficiency: the donor/acceptor ratio when the total energy transfer efficiency is 50% as defined in the main text) was a few. To overcome this low photon-harvesting efficiency, we designed and investigated a new nanosheet type light-harvesting system including phthalocyanine. As a result from steady-state and time-resolved fluorescence measurements, the energy transfer reaction was highly efficient even under the donor excess conditions. The efficiency was almost 100% even under the ratio of donor/acceptor = 1/1–6/1. The most advanced point of this study is the presence of energy transfer between nonadjacent donor–acceptor, and the photon-harvesting efficiency of this system progressed seven times compared to that of the previous porphyrin–porphyrin system. Additionally, the efficient utilization of visible region of sunlight (visible-light-harvesting efficiency: the percentage of visible region of sunlight (380–780 nm), in which the extinction coefficient of the light-harvesting molecules excesses 10 4 M –1 cm –1 ) was realized in the present donor–acceptor combination. The visible-light-harvesting efficiency of the present system reached 86%. Thus, our host–guest system took a step closer to realize an artificial light-harvesting system utilizing the wide-wavelength region of sunlight with high photon-harvesting efficiency, in which a few energy acceptor molecules can harvest the excitation energies from a large number of adjacent and/or nonadjacent donor molecules efficiently.