Coherent external and internal phonon oscillations in organic molecular crystals

Summary form only given. Thin organic films with semiconducting properties are highly interesting for device applications such as charge transport layers, organic LED, and solar cells. However, the phonon properties of organic crystals, which are important for e.g. exciton self-trapping, are very little understood. Because self-trapping might be critical for the realization of emission devices, a detailed investigation of the exciton-phonon interaction is required.We have directly time resolved coherent phonon oscillations in polycrystalline thin films of MePTCDI (N-N'-dimethylperylene-3,4,9,10dicarboximide) employed as a model system for quasi-one-dimensional organic molecular crystals. The measurements are carried out using a femtosecond pump-probe technique, in which an ultrashort pump pulse excites the sample and a time-delayed probe pulse measures the resulting transmission change as a function of pump-probe delay.