In this work, the highly ordered growth of large organic molecules was investigated by studying the quaterrylene derivatives QT, QTCDI, and QTCMI. In order to prepare and analyze layers composed of these molecules, an OMBE system was set up first. However, as OMBE represents only a standard technique for the preparation of ordered overlayers containing small and medium-sized organic molecules, it was not clear whether the concept could be successfully applied to these larger molecules\nas well. Regarding this issue, the thermal stability of the molecules was investigated by optical spectroscopy. The performed experiments revealed that QT molecules can be evaporated without thermal decomposition at approximately 350±C. In contrast, the sublimation temperature of QTCDI was found to be much higher, even above the decomposition temperature of the molecule. As a consequence, QTCDI evaporation is always accompanied by its decomposition, with QTCMI being one of the products.