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Keynote Speaker

Prof. Dr. Manuela Schiek

Center for Surface and Nanoanalytics, Johannes Kepler University, Linz, Austria

E-mail

manuela.schiek@jku.at

Imaging Mueller Matrix Ellipsometry for Spotting Molecular Excitons

talk by APL-Prof. Dr. Manuela Schiek
Center for Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz (Austria),
Optical Nanometrology, National Metrology Institute (PTB), Brunswick (Germany)

Quadrupolar anilino-squaraine dyes exhibit distinct excitonic signatures in their visible absorption spectra due to strong intermolecular interactions. These excitons are a result of the spatial arrangement of the molecular backbones, which is steered by non-chromophoric terminal functionalization patterns. In case of a particular micro-crystalline textured thin film (SQIB platelets), which is composed mainly of rotational domains with a single preferred orientation relative to the substrate, these excitons are predominantly Frenkel excitons [1]. Since these crystalline domains consist of an orthorhombic polymorph, an EP4 imaging ellipsometer allows the determination of the full diagonal dielectric tensor [2]. The tensor components represent the excitonic transitions and reveal multiple Davydov splittings, including a dark state for this polymorph containing multiple non-equivalent molecules within the primitive unit cell. Combined with structural and morphological analysis using X-ray diffraction and atomic force microscopy, a complete picture of the molecular alignment and the spatial anisotropy of excitonic transitions is obtained. Once this is known, polarized spectroscopic transmission intensity mapping with the EP4 enables, for example, the identification of different polymorphs in distinct crystalline domains based on their characteristic polarized absorbance pattern [1].

[1] Balzer, Breuer, Witte, Schiek. Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films. Langmuir 38 (2022) 9266.

[2] Funke, Duwe, Balzer, Thiesen, Hingerl, and Schiek Determining the Dielectric Tensor of Microtextured Organic Thin Films by Imaging Mueller Matrix Ellipsometry. J. Phys. Chem. Lett. 12 (2021) 3053.

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