Dresden 2017 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 38: Organic-Inorganic Hybrid Systems and Organic Films V

O 38.1: Hauptvortrag

Dienstag, 21. März 2017, 14:00–14:30, WIL A317

Tuning excitonic excitations in molecular layers — •Martin Weinelt and Cornelius Gahl — Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany

Excitons constitute the fundamental optical excitations in organic materials. Here intermolecular interactions lead to delocalization and transport of excitons and thereby influence the response of the molecular film. We will discuss two examples where excitonic excitations play an important role.

In azobenzene-alkanethiolate self-assembled monolayers quenching of the optical excitation by the supporting gold substrate is avoided by decoupling the azobenzene chromophore via an alkane linker. However, intermolecular coupling in the SAM strongly shifts and broadens the absorption bands. One strategy to reestablish efficient photoisomerization is to introduce additional molecules as lateral spacers. As a consequence the excitonic coupling of the chromophores can be tuned between single molecules and aggregates, which strongly influences optical switching.

Sexithiophene/gold is a model system for an organic semiconductor/metal - interface. Here we investigated the exciton dynamics by time-resolved two-photon photoemission spectroscopy. We show that resonant excitation and vibrational dissipation of excess energy both lead to exciton population on an ultrafast time scale resulting in a long lived final state. Again the morphology of the organic layer (crystalline vs amorphous) strongly influences the excited state dynamics and energetics relevant for organic electronics.