In the present thesis, three different molecular materials were investigated spectroscopically. Furthermore, the spectroscopic methods have been set up or extended. Among these methods is an experimental setup for photoluminescence excitation measurements at cryogenic temperatures, intended for investigations of the population dynamics of charge-transfer (CT) excitons in molecular solids is designed, constructed and characterized. Initially a series perylene derivatives were investigated. These derivatives are promising materials for a variety of technical applications, among others as car paints, pH sensors or as building blocks of organic solar cells. In the framework of this thesis, special donor-acceptor molecules have been synthesized, which can be viewed as an intramolecular internal interface. The aim was to determine the charge transfer rates and subsequently control the rates by various synthetic and experimental methods. At the heterointerface between donor- and acceptor-type molecular solids, so-called CT excitons can form. The study of CT excitons is crucial from a technical point of view - in regards to device optimization of organic solar cells - but also from the point of view of the fundamental research. In the context of the work, findings regarding the population behavior of the CT state in the pentacene-perflouropentacene material system. The obtained results could potentially have a fundamental importance for the understanding of CT states. It was found that a hole transfer from acceptor to donor material does not lead to a measurable CT luminescence signal. However, the reverse case of electron transfer from donor material yields a distinct CT luminescence signal. The samples used for the studies performed in this thesis are of highest structural quality. Hence, the experimental results could be clearly identified as an interfacial effect. By studying different molecular orientations at the interface, the assumption of increased electronic coupling could be confirmed in the case of a so-called Pi-stacking of the molecules. For the first time, a CT signal could be measured directly at a well-defined interface for the pentacene-C60 material system. Furthermore, the measurements reveal that a long-range effect influences the dynamics of C60 luminescence and the mobility of excited states.
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