We have been investigating complexes composed of anionic nanolayered materials such as clay nanosheets and cationic dye molecules. It was found that the structure of dye assembly on the layered materials can be effectively controlled by the use of electrostatic host−guest interaction called as "Size-matching Effect" or "Intercharge Distance Matching Effect". The intermolecular distance, the molecular orientation angle, the segregation/ integration behavior, and the immobilization strength of the dyes can be controlled in the clay−dye complexes (Fig. 1). Unique photochemical reactions such as energy transfer through the use of this methodology have been examined. Almost 100% efficiency of the energy-transfer reaction was achieved in the clay−porphyrin complexes as a typical example for an artificial light-harvesting system. Control of the molecular orientation angle is found to be useful in regulating the energy-transfer efficiency and in preparing photofunctional materials exhibiting solvatochromic behavior. In this paper, we will talk on the enhancement of photochemical properties of dyes on the clay surface such as fluorescence enhancement and efficient energy transfer systems in clay-dye complexes. A unique phenomenon of the strong enhancement in the fluorescence quantum yield (φf) and the excited lifetime (τ) of tetra-cationic porphyrazine dye (Pz) upon a complexation with inorganic nanosheets were observed. Although Pz does not strongly fluoresce in a bulk solution (φf = 0.01, τ = 0.1 ns), φf and τ increased up to 19 and 34 times by an intercalation into stacked clay nanosheets. Steady-sate and time-resolved fluorescence measurements revealed that this strong enhancement in φf and τ is derived from the suppression of nonradiative deactivation pathways of Pz by a complexation with clay nanosheets. We here name this phenomenon a “Surface-Fixation Induced Emission (S-FIE)”. By using such favorable photochmeical character, light harvesting system where the efficiency was almost 100% even under the ratio of donor/acceptor = 1/1−6/1 was achieved. Ref. S. Takagi et al. Langmuir (Invited Feature Article) 2013, 29, 2108–2119; Langmuir 2013, 29, 1748–1753; J. Phys. Chem. C 2013, 117, 9154–9163; J. Phys. Chem. C 2014, 118, 10198–10203; J. Phys. Chem. C 2014, 118, 20466–20471.

Artificial light harvesting system composed of organic dyes and clay minerals

249th National Meeting (2015)

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