Direct Visualization of Energy-transferred Excited State in Eu Complex

Highly luminescent lanthanide (Ln) complexes have attracted much attention because Ln³⁺ ions show long-lived ff-emissions with narrow band shape. Their unique photo-optical properties are promising for the design of light-emitting materials and sensing devices. Although the ff-emissions are essentially weak because of Laporte forbidden, chelate ligands is effective to strengthen the intramolecular energy transfer from photo-excited organic ligands to Ln³⁺ ions. The direct evidence of energy transfer from ligands to Ln³⁺ and details of excited state, however, are still veiled. Here, we report direct visualization of energy-transferred excited state in Eu complex with a hexadentate ligand (L) consisting of two bipyridine moieties bridged by an ethylendiamine unit, [Eu³⁺(L)(NO₃)₂](PF₆) (Eu(L))[1] by Maximum Entropy Method (MEM) charge density[2] and electrostatic potential analysis[3] based on SR X-ray diffraction. First, we confirmed that the electron numbers of Eu and ligand L in the excited state are the same as those in the ground state, which is a direct evidence of energy transfer instead of charge transfer. Next, we observed charge re-distribution in the Eu ion and the ligand L. The electrostatic potential distributions calculated using MEM charge density give an experimental evidence for the existence of polarization of ligand L both in the ground and photo-excited states. The orientation polarization in the ground state changed during pumping at 315 nm, and the charge re-distribution are qualitatively consistent with a theoretical prediction. This characteristic luminescence behavior based on the energy relaxation process have not been detected by fundamental crystal structural analysis. We have succeeded in visualization of subtle but important change due to energy transfer in the mononuclear Europium complex with hexadentate ligand at the first time.

Nanocrystallization and Electronic-Conductivity Enhancement in PEDOT:PSS films

The conductive organic polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate), abbreviated as PEDOT:PSS, is widely used in capacitors, antistatic coating etc. and one of the potential materials for the next-generation printable electronics. It is because of its excellent dispersibility in water and high electronic conductivity of more than 1,000 S/cm. Although many preceding studies have provided a variety of possible mechanisms of high conductivity, such as charge transfer between PEDOT and residual solvents, there has been no conclusive explanation for the origin of the high conductivity. Here, we report the nanometer-size crystallization of PEDOT inside the hydrophobic core region of PEDOT:PSS in a solid film and enhancement of electronic conductivity caused by the nanometer-size crystal growth of PEDOT. The structure of PEDOT:PSS has been investigated by means of small- and wide-angle X-ray scatterings (SAXS and WAXS) using high brilliance synchrotron radiation light source in SPring-8, Japan. We have obtained the microscopic structural model of PEDOT:PSS micelle in the water dispersion and the solid polymer film (Fig. 1(a)). Nanometer-size crystals of PEDOT were grown during the course of film fabrication in the wet process from the water dispersion. Furthermore, we found that the better crystallinity of the PEDOT crystal in the films prepared in the different conditions resulted in the higher electrical conductivity (Fig. 1(b)). The result suggests that the size of the crystallite is one of the key parameters for the enhancement of the electronic conductivity in PEDOT:PSS films. These findings shed light on the further improvement of the electrical conductivity of PEDOT:PSS polymer films by controlling the evaporation to dryness in the wet fabrication process.

The 100 Years History of Crystallography in Japan

A century ago, crystallogtaphy ushered in the era of modern science & technology in Japan. The beginning of modern crystallography in Japan dates back to 1913. Torahiko Terada (Tokyo Imperial University) demonstrated X-ray diffraction[1] and Shoji Nishikawa (Tokyo Imperial University) reported on X-ray patterns of fibrous, lamellar and granular substances[2]. In 1936, Ukichiro Nakaya (Hokkaido University) successfully classified natural snow crystals and made the first artificial snow crystals. In the last half-century, developments in crystallography helped form thriving manufacturing sectors such as the semiconductor industry, the iron and steel industries, the pharmaceutical industry, the electronics industry, the textile industry, and the polymer industry, as well as a wide array of academic research.

Instrumentation of SAXS for the Analysis of Heterogeneous Structure in Polymer

Polymer materials have hierarchal structure in the very wide range of scale. It is well known that the property is dependent on the hierarchical structure. In order to improve the performance of the materials, clarifying the hierarchical structure in a wide range and the feed back to the manufacturing process are important. However, it is difficult to clarify the hierarchical heterogeneous structure of polymer materials using only single method. Therefore the combination of microbeam small- and wide- angle X-ray scattering (SAXS/WAXS) is useful for evaluation of the hierarchical heterogeneous structural of polymer materials. The BL03XU, in alias, FSBL, in SPring-8 was constructed by consortium of industrial and academic groups and has been used from 20101),2). Structure characterization of advanced materials in the industrial field has been carried out using microbeam SAXS/WAXS method. In addition to the description of the SAXS/WAXS measurement system at BL03XU, we will report on the local structural evaluation of carbon fiber (CF). A hierarchal heterogeneous structure of CFs was visualized in the space resolution of 1 μm using a microbeam and an X-ray imaging technique. The image contrasts were identified by the difference in peak positions corresponding to the void size, the peak width corresponding to the crystallite size, and intensities corresponding to the amount of crystallites and voids. The X-ray scattering images of high-modulus CF are shown in a figure. Nanometer-size voids estimated by SAXS are abundant in the center of a fiber, on the other hand, the crystallite is abundant in the vicinity of a surface was revealed. It is suggested that the voids were generated near the center of the fiber to relax the strain during the crystallization process from the surface during the graphitization of fibers. We succeeded in visualizing the distribution of voids and crystallite of a few nanometers, which cannot be observed by an X-ray transmission imaging method.