Stephanie Hanning

Investigation of FIrpic in PhOLEDs via LC/MS technique

The commercial breakthrough of phosphorescent organic white light sources is presently hampered due to the unavailability of a stable blue phosphorescent emitter material. Moreover, only few analytical investigations have been made regarding the chemical degradation of the phosphorescent emitter materials during the processing or the operation of the devices.Organic light emitting devices (OLEDs) containing phosphorescent metal complexes with iridium as central ion were investigated. Special attention was paid to the chemical degradation of the material. The devices were analyzed by means of high performance liquid chromatography coupled with mass spectrometry (HPLC/MS). Electron spray ionization (ESI) was employed as ionization source. Isomerization phenomena of the blue-green emitting heteroleptic iridium complex FIrpic could be observed after the device manufacture and after operation. These findings could give hints on the mechanisms that influence the lifetime of PhOLEDs based on FIrpic or similar blue emitters.

Study on microscopic homogeneity of polymeric candidate reference materials BAM H001–BAM H010 by means of synchrotron µ-XRF and LA-ICP-MS

In this study the microscopic homogeneity of the newly developed plastic reference materials BAM H001–BAM H010 was investigated. The materials consist of an acrylonitryle-butadien-styrene terpolymer, doped with different amounts of the elements Br, Cd, Cr, Hg and Pb. For the quantitative determination of the degree of homogeneity, a procedure proposed by Kempenaers et al. (Fresenius J. Anal. Chem., 2001, 369, 733–737) was used. On every sample an extensive number of different points were analyzed and standard deviation for every element mentioned above was used to calculate a minimal sampling mass that is necessary to reach a certain level of uncertainty caused by inhomogeneity (mmin,5%). The experiments were taken out with synchrotron µ-XRF (SR µ-XRF) at BESSYII in Berlin and by laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS). The calculated values for mmin,5% of both techniques showed comparable results for all elements. It could be shown that the materials are suitable for calibration of micro analytic techniques if at least 64 µg are used.

Comparative study on the homogeneity of polymeric calibration materials using LA-ICP-MS

The production of polymeric calibration standard materials with sufficient homogeneity for the calibration of analytical methods with high lateral resolution like LA-ICP-MS was investigated. An index η* was introduced to compare the homogeneities of different acrylonitrile butadiene styrene terpolymer (ABS) based samples. It was demonstrated, that elements present in organic compounds could be introduced into polymeric materials with a higher homogeneity than inorganic compounds without special treatment. For organic Br compounds, a 20 to 30 times higher value for η* was found than it was for the case of AgBr. For Pb stearate and Pb acetate, 10 times higher values for η* were found than was the case for PbCrO4. For PbO, it is shown that multiple extrusion and mechanical treatment can improve the homogeneity of certain inorganic compounds as particle sizes are decreased during the extrusion.