Manipulation of supramolecular 2D assembly of functional dyes toward artificial light-harvesting systems

Abstract

Abstract:In recent years, excellent research has revealed that light-harvesting systems (LHSs) are composed of beautifully aligned chlorophyll molecules; the regulated alignment of chlorophylls is responsible for the efficient and selective light-harvesting energy transfer processes in purple bacteria. This finding led to the construction of a regularly arranged assembly of functional dyes as a step toward fabricating artificial LHSs. While most approaches toward the construction of dye assemblies have depended on molecular interactions such as covalent, coordination, and hydrogen bonds, my approach involves guest-host interactions using an inorganic nanosheet as the host material. This short review presents the construction of a 2D dye assembly and its effective utilization in artificial light-harvesting applications. Owing to the highly stable and uniform 2D alignment of functional dyes on inorganic nanosheets, nearly 100 % singlet-singlet energy transfer and efficient light-harvesting were achieved. I believe that the results presented herein will contribute to the construction of efficient photochemical reaction systems in supramolecular host-guest assemblies, which may facilitate the realization of artificial photosynthesis.

Distinctive stability of a free-standing monolayer clay mineral nanosheet via transmission electron microscopy

“…[1][2][3] Among the many types of clay minerals, smectite groups (e.g., saponite, montmorillonite) are frequently used owing to their moderate anionic charge density, imparting exfoliation (or stacking) ability to individual nanosheets in aqueous solutions as well as optical transparency in the visible light region in the exfoliated state at small particle sizes. [4][5][6][7] Smectite possess the following chemical formula: [(Si 8-x Al x )(Mg 6y Al y )O 20 (OH) 4 ](x-y)Y + , where Y represents the cations to balance the charges, and they possess layers consisting of a 2:1 ratio of tetrahedral and octahedral sheets, with a thickness of 0.96 nm. Completely exfoliated clay mineral, as a single layer, can be defined as a family of two-dimensional (2D) nanosheets.…”

“…22 Once non-destructive direct imaging of clay mineral nanosheet or useful clay mineral-based organicinorganic hybrid materials at the atomic scale is established, it will strongly promote their applicability such as selective adsorption for heterogeneous catalyst or sensing, 23 or photoenergy conversion. 5 We recently achieved atomic-scale imaging of a freestanding (i.e., without any surfactants or supporting matrices) monolayer clay mineral by annular dark-field (ADF) STEM. 22,24 The monolayer clay mineral was observed at the atomic-scale without any destruction, although bulk clay minerals are generally sensitive to the electron beam irradiation, as reported for cross-sectional imaging at the atomic-scale via (S)TEM.…”

Atomic-Scale Imaging of a Free-Standing Monolayer Clay Mineral Nanosheet Using Scanning Transmission Electron Microscopy

“…In our previous work, we used anionically charged clay nanosheets as a host material to build a supramolecular 2D assembly of cationic guest molecules via electrostatic interaction. , Clay nanosheets are attractive ultrathin 2D nanomaterials characterized by (1) nanostructured flat sheets at the atomic level, (2) negatively charged surface, (3) exfoliation or stacking ability of individual nanosheets in aqueous solution, and (4) optical transparency in the visible light region in the exfoliated state at small particle size (ca. <200 nm). − Among lots of clay minerals, smectite group of minerals (e.g., saponite, montmorillonite) is frequently used owing to its moderate anionic charge density, which can achieve exfoliation in water.…”

Room temperature phosphorescence from a guest molecule confined in the restrictive space of an organic-inorganic supramolecular assembly

“…Guest@OAm 2 16+ represents a protonated capsular assembly having 16 positive charges enclosing aromatic guest molecule. As Takagi's group has already established for porphyrins or other dyes 13,14 , capsules have the ability to be stably arranged on a saponite surface (Figure 1b) without any unfavorable ground-state interactions such as aggregation and self-quenching [15][16][17] . Although guest@OAm 2 16+ has 16 positive charges, it behaves like a tetracationic porphyrin, with only the 4 cationic charges at the bottom anchored to the clay surface.…”