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., <i>J. Am. Chem. Soc.</i> <b>2011</b>, <i>133</i>, 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 10⁴ 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