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O: Fachverband Oberflächenphysik

O 46: Organic molecules on inorganic substrates: electronic, optical and other properties – Poster

O 46.6: Poster

Dienstag, 10. März 2026, 14:00–16:00, P2

Fluorescence Spectroscopy of Quinacridone Molecules on thin Epitaxial KCl(100) films. — •Morris E. L. Mühlpointner and Moritz Sokolowski — Clausius-Institut für Physikalische und Theoretische Chemie der Universität Bonn, Germany

Quinacridone forms one-dimensional chains on metal surfaces and thin epitaxial KCl films grown on Ag(100) [1]. TD-DFT predicts the transition dipole moment in the direction of chain growth. The resulting J-like coupling suggests superradiance which can be enhanced by chemical modifications that increase the inter-chain distance. However, no data on the optical properties of QA on KCl surfaces exist.

We have measured the fluorescence at cryogenic temperatures (7 K) of quinacridone (QA) and its fluorinated derivative (FQA) on ultrathin KCl films grown on Ag(100). Isolated QA molecules on KCl have a 0-0 transition at 20200±200 cm^-1. The spectral lines have asymmetric shapes with large line widths (400 to 700 cm^-1). We relate the broadening to the weak bonding interactions of the molecule and the substrate.

Upon forming a 2D aggregate on the surface, we observe a significant red shift by 1600 cm^-1 for QA and FQA. This can be understood by the attractive of the transition dipoles.

[1] JPCC 127 (2023): 23814-23826.

Acknowledgements: We thank the DFG for support via the research training group 2591, Mohammad Al Dubel and Sigurd Höger for kindly providing FQA molecules and Harshita Malik and Thomas Bredow for DFT calculations.

Keywords: Quinacridone; Fluorescence; KCl; Ag(100)