Berlin 2024 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 31: Poster: Organic Molecules on Inorganic Substrates
O 31.9: Poster
Dienstag, 19. März 2024, 18:00–20:00, Poster C
Electronic Properties of N-Heterotriangulene Derivatives Adsorbed on Au(111) Investigated with Two-Photon Photoemission Spectroscopy — •Jakob Steidel1, Ina Michalsky2, Milan Kivala2, and Petra Tegeder1 — 1Physikalisch-Chemisches Institut, Universität Heidelberg, Germany — 2Organisch-Chemisches Institut, Universität Heidelberg, Germany
In many organic opto-electronic devices donor-acceptor systems (D-A systems) play a crucial role, for example as the emitting layer in organic light emitting diodes or to enhance charge separation in organic photovoltaics. Triphenylamine derivatives like the planar N-Heterotriangulene-550 (N-HTA-550) are promising electron donors. The introduction of an etheno bridge closes a seven membered ring in N-HTA-557 and strongly modifies the electronic structure of the molecule while retaining its steric demands. By oxidation of the etheno bridge and subsequent condensation with quinoxaline-2,3-diamine N-HTA-557-P, an intramolecular D-A system, is synthesized. In the present contribution we investigate the electronic structure of N-HTA-550, N-HTA-557 and N-HTA-557-P adsorbed on Au(111) with two-photon photoemission spectroscopy (2PPE). In agreement with the results of UV/Vis-absorption spectroscopy we found the optical gap of N-HTA-550 and N-HTA-557-P to be 3.7 eV and 2.6 eV respectively. For N-HTA-557 the electron affinity level and occupied molecular states were determined, yielding a fundamental gap of 2.9 eV. By means of femtosecond time-resolved 2PPE two coverage dependent exciton decay pathways in thin films of N-HTA-557-P were identified.
Keywords: Two-Photon Photoemission; Donor-Acceptor Systems; Organic Semiconductors