Effects of the Surface Charge Density of Clay Minerals on Surface-Fixation Induced Emission of Acridinium Derivatives

Surface-fixation induced emission is a fluorescence enhancement phenomenon, which is expressed when dye molecules satisfy a specific adsorption condition on the anionic clay surface. The photophysical behaviors of two types of cationic acridinium derivatives [10-methylacridinium perchlorate (Acr+) and 10-methyl-9-phenylacridinium perchlorate (PhAcr+)] on the synthetic saponites with different anionic charge densities were investigated. Under the suitable conditions, the fluorescence quantum yield (Φf) of PhAcr+ was enhanced 22.3 times by the complex formation with saponite compared to that in water without saponite. As the inter-negative charge distance of saponite increased from 1.04 to 1.54 nm, the Φf of PhAcr+ increased 1.25 times. In addition, the increase in the negative charge distance caused the increase in the integral value of the extinction coefficient and the radiative deactivation rate constant (kf) and the decrease in the nonradiative deactivation rate constant. It should be noted that the 2.3 times increase in kf is the highest among the reported values for the effect of clay. From these results, it was concluded that the photophysical properties of dyes can be modulated by changing the charge density of clay minerals

Dense Deposition of Gold Nanoclusters Utilizing a Porphyrin/Inorganic Layered Material Complex as the Template

We examined the deposition of gold clusters through the reduction of a gold precursor sensitized by nonaggregated, assembled porphyrin molecules on an inorganic layered material surface in order to develop a novel strategy for constructing assemblies of gold clusters. Visible light irradiation on nonaggregated, assembled porphyrin on the inorganic surface in the presence of the gold precursor and an electron donor induced the deposition of gold NPs on the surface of the inorganic layered material. Uniform gold clusters, with an average diameter of 1.5 nm, were deposited on the surface without aggregation. The average interparticle distance between adjacent gold clusters (center to center) was 2.3 nm, which agrees well with the average intermolecular distance of the nonaggregated, assembled porphyrin molecules on the inorganic surface. Thus, the generated gold clusters appear to reflect the nonaggregated, assembled structure of the porphyrin molecules on the inorganic surface. This method, termed the photosensitized template reduction (PTR) method, is a useful and novel technique for the deposition of metal nanoparticles on the surfaces of supporting materials