Energy Transfer among Three Dye Components in a Nanosheet–Dye Complex: An Approach To Evaluating the Performance of a Light-Harvesting System

Energy transfer among three dye components, namely, <i>p</i>-2,4,5,7-tetrakis­(<i>N</i>-methylpyridinium-4-yl)-6-potassium-oxy-3-fluorone (Fluorone), <i>meso</i>-tetra­(<i>N</i>-methyl-3-pyridyl) porphine (<i>m</i>-TMPyP), and <i>meso</i>-tetra­(<i>N</i>-methyl-4-pyridyl)­porphine (<i>p</i>-TMPyP), was investigated for the purpose of utilizing a wide range of sunlight wavelengths for clay nanosheets. In this paper, we define a new parameter, the enhancement ratio of the excitation frequency (Γ_{380–780 nm}) of the dye, in order to comprehensively represent the performance of the light-harvesting system (LHS). Γ_{380–780 nm} is defined as the enhancement ratio of the excitation frequency of dye that has the lowest excitation energy in the system (<i>p</i>-TMPyP in this system) in terms of the frequency of <i>p</i>-TMPyP without the use of light-harvesting dyes (Fluorone and <i>m</i>-TMPyP), when the visible-light region of sunlight (380–780 nm) is used for irradiation light. Γ_{380–780 nm} was calculated from the absorption spectra of dyes, the results of energy transfer experiments, and the sunlight spectrum (380–780 nm). We found that Γ_{380–780 nm} in our LHS is 2.4, which implies enhancement of the excitation frequency of <i>p</i>-TMPyP by 2.4 times relative to that of <i>p</i>-TMPyP without a light harvesting system. We believe that Γ_{380–780 nm} is an important standard parameter of the performance of artificial LHSs