Morphology dependent fluorescence in α-sexithienyl thin film at 4.2k

We investigated by fluorescence spectroscopy at 4.2K high vacuum sublimated thin films of α-sexithienyl grown on mica upon a systematic variation of the growth parameters. We studied how the film morphology, induced by different conditions of growth (thickness and substrate temperature), acts on the emission properties at the early stages of growth. We show how the increased molecular order corresponds to a less efficient excitation energy transfer to low energy levels (due to the presence of defects and aggregates) and to an enhanced excitonic character of the fluorescence.