Temperature-dependent study of vibration and polymorphism of oligoacenes and their derivatives

Raman measurements have been performed on a series of oligoacenes and their derivatives (anthracene, tetracene, pentacene and diphenyl-anthracene, rubrene) in a wide temperature range (50-300K). It has been observed that different phases co-exist in several of these crystals depending on sample preparation and history, and that transitions between polymorphs can be observed as a function of temperature. Comparisons among crystals with similar molecular structure will be made to clarify the changes in the inter- and intra-molecular modes as the structure changes with temperature. Simulated calculations of the inter-molecular modes between multiple molecules, and the intra-molecular modes of the isolated molecules will also be presented.