Regensburg 2025 – scientific programme
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DS: Fachverband Dünne Schichten
DS 15: Organic Thin Films, Organic-Inorganic Interfaces
DS 15.4: Talk
Friday, March 21, 2025, 10:45–11:00, H3
Excited state dynamics in thin films of planar and twisted azaperopyrene derivatives — •Jakob Steidel1, Robert Eichelmann2, Jakob Sawatzki1, Lutz Gade2, and Petra Tegeder1 — 1Physikalisch-Chemisches Institut — 2Anorganisch-Chemisches Institut, Universität Heidelberg, Germany
Azaperopyrene derivatives are a class of organic semiconductors with a high potential for applications in optoelectronic devices. The molecular π-system of planar octaazaperopyrenedioxide (OAPPDO-H) is substituted with chlorine yielding OAPPDO-Cl, a molecule with a twisted structure.
In this contribution we utilised transient absorption spectroscopy to elucidate excited state dynamics of OAPPDO derivatives with planar and twisted molecular π-systems in thin films. On a short time scale of several hundred femtoseconds we observed fast population of excited states and fluorescence in both materials. The lifetimes of these processes show a similar dependency on the intensity of the excitation pulse. On a long time scale of several nanoseconds striking differences were observed. While the lifetimes of the excited state in OAPPDO-Cl increased and saturated with increasing excitation intensity, the lifetimes in OAPPDO-H showed a maximum at a medium excitation intensity of 400 nJ per pulse. We assign this behaviour to the opening of an additional decay pathway due to triplet-triplet-annihilation that requires cofacial arrangement of two molecules. Only planar OAPPDO-H can arrange in such a way, while the increased steric hindrance in OAPPDO-Cl suppresses this intermolecular interaction.
Keywords: Transient Absorption Spectroscopy; Organic Semiconductors; Triplet-Triplet-Annihilation