“In-water” Dehydration Reaction of an Aromatic Diol on an Inorganic Surface

The effect of a synthetic saponite surface on the “in-water” dehydration reaction of diol was examined using 4-formyl-1-methylquinolinium salt (MQu+) as a substrate. The equilibrium between aldehyde (MQu+-Aldehyde) and diol (MQu+-Diol) was affected by the surrounding environment. The equilibrium behavior was observed by 1H nuclear magnetic resonance (NMR) and UV–vis absorption measurements. Although MQu+ was completely in the form of MQu+-Diol in water, the equilibrium almost shifted to the MQu+-Aldehyde side when MQu+ was adsorbed on the saponite surface in water. In addition, the MQu+-Aldehyde ratio depended on the negative charge density of saponite. The factors that determine MQu+-Aldehyde: MQu+-Diol ratio were discussed from the thermodynamic analysis of the system. These data indicate that the electrostatic interaction between the charged saponite surface and MQu+ stabilized the aldehyde side enthalpically and destabilized it entropically. The major reason for these results is considered to be the difference in adsorption stabilization between MQu+-Aldehyde and MQu+-Diol on saponite surfaces

Monolayer Modification of Spherical Amorphous Silica by Clay Nanosheets

Clay-silica nanocomposite materials (CSiN) were prepared by an electrostatic interaction between negatively charged clay nanosheets and positively charged spherical silica, which was modified with an alkyl ammonium group by silane coupling. By optimization of the preparation conditions, 84% coverage of the silica surface by the clay nanosheets was achieved. Adsorption experiments using cationic porphyrin dyes on the CSiN revealed that the clay nanosheet covers the spherical silica as a single layer and does not detach from the silica surface under aqueous conditions. In addition, it turned out that the cationic porphyrin dye did not penetrate the space between the silica surface and the clay nanosheet. Porphyrin molecules were adsorbed only at the outer surface of the clay nanosheet without molecular aggregation even under the high-density adsorption conditions. By combining spherical silica and clay nanosheets, it is possible to prepare novel hybrid materials where the surface can act as a unique adsorption field for dyes

Structural Transformation of Azonia[5]helicene Photoproduct via Reaction Field Function of Layered Inorganic Material

In an attempt to generalize “on surface synthesis”, which has unique potential in the area of organic synthesis, the focus was placed on layered silicates having a highly flat surface. The photoreaction of (±)-13-bromo-6a-azonia[5]­helicene (AHHBr) and (±)-2-bromo-13-methyl-6a-azonia[5]­helicene (AHBrMe) in solution and within the layers was examined. In the case of AHBrMe, the photoproduct was different from that in solution. 1H nuclear magnetic resonance (NMR), Fourier transform-infrared spectroscopy (FT-IR), and electrospray ionization-mass spectrometry (ESI-MS) measurements revealed that the photoproduct obtained within the layers was a benzo-perylene molecule with a completely flat lactone structure (AL). This study is the first example of the successful conversion of a chemical reaction path due to the steric effect of the flat surface of layered silicate

Emission Enhancement of Anthracene Derivative Caused by a Dramatic Molecular Orbital Change on the Nanosheet Surface

The emission enhancement phenomenon on clay nanosheets is called surface-fixation-induced emission (S-FIE) and is similar to aggregation-induced emission, which has attracted the attention of many researchers. Both emission enhancement phenomena are primarily caused by the suppression of nonradiative deactivation. In this study, a new S-FIE molecule was synthesized and its basic photochemical behavior was investigated. The emission enhancement of the new molecule on the clay surface was induced by the suppression of nonradiative deactivation and acceleration of radiative deactivation. Density functional theory calculations indicated that the acceleration of radiative deactivation originated from the improvement in the spatial overlap between the two molecular orbitals related to the emission phenomenon and the increase in the Frank–Condon factor