Abstract
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.
Highlights
Organic fluorescent dyes have attracted great attention as probes, sensors, display materials such as organic light-emitting diodes (OLEDs) and fluorescent sheets, and even as optoelectronics materials.[1−7] Organic dyes have been widely used in these fields because they are composed of universal elements such as C, N, and O and have less environmental impact compared with inorganic phosphors containing transition elements,[8,9] and typical quantum dots contain harmful substances such as Cd and In.[10−12] In devices such as OLEDs and fluorescent sheets, organic dyes are expected to be used in a solid state
Since clay minerals have a flat surface at the atomic level, can be exfoliated into a single layer, and have optical transparency in a solution state, they have been investigated as photo-functional host materials.[26−35] fluorescence enhancement by complexing clay minerals and methyl viologen was reported in 1986,36,37 the systematic study was not conducted since an aggregation formation of dyes on the clay surface takes place.[38−40] we found a phenomenon called the size-matching effect, in which the specific cationic molecules such as multicationic porphyrins are adsorbed on the clay surface without
An increase in kf and a decrease in knr were observed. These changes of photophysical properties indicate the suppression of the mobility of the rotational substituent by the flattening of the dihedral angle between the rotational substituent and acridinium ring when PhAcr+ was adsorbed on the clay surface
Summary
Organic fluorescent dyes have attracted great attention as probes, sensors, display materials such as organic light-emitting diodes (OLEDs) and fluorescent sheets, and even as optoelectronics materials.[1−7] Organic dyes have been widely used in these fields because they are composed of universal elements such as C, N, and O and have less environmental impact compared with inorganic phosphors containing transition elements,[8,9] and typical quantum dots contain harmful substances such as Cd and In.[10−12] In devices such as OLEDs and fluorescent sheets, organic dyes are expected to be used in a solid state. This paper reports and discusses the photophysical behavior and fluorescence enhancement of mono-cationic acridinium derivatives (Acr) on the clay surface by using two acridinium derivatives as guest molecules (Figure 1) and four synthetic saponites which have different negative charge densities as host materials.
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