Abstract

Some interesting physical properties of organic molecular crystals such as exciton and change carrier transport are found to depend sensitively on trace impurities even if these molecules are present only on a ppm or sub-ppm scale. Impurities often exhibit close molecular similarity to the matrix compound, a fact which makes their analytical detection and their separation even more difficult. We wish to summarize some of the analytical techniques which can be applied under these circumstances: gas chromatography, mass spectrometry, liquid chromatography, sensitized fluorescence emission, delayed fluorescence, triplet exciton lifetime, thermally activated current spectroscopy, including time-resolved measurements of trap-controlled charge carrier mobilities, and radical ion photocurrent excitation spectroscopy. The different methods are compared under the aspects of sensitivity, selectivity, universality and lower detection limit.

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