Tanvir A. Amit

The use of organic light-emitting diodes (OLEDs) as screen display materials has become very attractive because they offer higher energy saving and richer colors compared to liquid crystal displays (LCDs). However, impurities present in the OLED materials can adversely impact device lifetime, stability, and overall performance. Isolation of OLED compounds from synthetic impurities can be challenging using the traditional purification (i.e., train sublimation). We investigated the use of supercritical fluid chromatography (SFC) to separate OLED compounds as an alternative technique for profiling impurities and compound purification. We investigated the use of SFC to analyze a combination of OLED model compounds of different classes. The separation behavior of four different chromatographic columns containing the stationary phases 1-aminoanthracene, naphthyl, and 2-ethylpyridine was examined via SFC using CO2 as the main mobile phase component. The effect of three different mobile phase co-solvents (i.e., methanol, acetonitrile, and tetrahydrofuran) on the separation selectivity and resolution was also investigated in addition to the effect of temperature, pressure, and flow rate. For the model compounds used, the naphthyl column and a CO2 mobile phase modified with tetrahydrofuran provided the best separation in terms of resolution. The SFC analysis showed high resolution and short analysis time compared to HPLC and provided for the separation of small sample impurities. Based on such column screening and method development strategy, various other proprietary OLED materials were purified using semi-preparative SFC.