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Abstract
Screen technology for “smart” devices continues to advance as researches seek to enhance display performance by reducing energy consumption and improving color characteristics. To that end, researchers are turning to organic light-emitting diodes (OLEDs) as the display materials due to higher energy saving and richer color compared to liquid crystal displays (LCDs). However, one major setback of the OLED technology is that the devices are very sensitive to the impurities present in the OLED materials, impacting device lifetime, stability, and overall performance. The isolation of large quantities of the main OLED components from the synthetic impurities is challenging using the traditional purification process (i.e., train sublimation), which has poor reproducibility, and high capital and operating cost. Supercritical fluid chromatography (SFC) could lend itself as an alternative technique for the profiling of impurities and their purification. In this study, we investigated the use of SFC to analyze a mixture of amorphous monomeric molecular glasses with charge-transporting property typical of OLED materials. The separation behavior of four different chromatographic columns containing the stationary phases 1-aminoanthracene (1-AA), naphthyl, 2-ethylpyridine, and C-18 were examined to perform the SFC separations. The effect of using three different co-solvents (i.e., isopropyl alcohol, acetonitrile, and tetrahydrofuran) to the CO2 mobile phase on the separation selectivity and resolution was also investigated. For the probe mixture used, the naphthyl column in combination with the addition of acetonitrile as co-solvent provided the best separation in terms of resolution. The SFC method was farther optimized for co-solvent composition, temperature, pressure, and flow rate. The SFC analysis showed high resolution and short analysis time compared to HPLC, and also provided for the separation of small components that have been attributed to impurities in the sample.
