SKM 2021 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 5: Poster Session I

CPP 5.17: Poster

Dienstag, 28. September 2021, 17:30–19:30, P

Polarization Resolved Optical Spectroscopy of PEN:PFP Charge-Transfer Excitons — •Darius Günder¹, Ana M. Valencia^2,3, Michele Guerrini^2,3, Tobias Breuer¹, Caterina Cocchi^2,3, and Gregor Witte¹ — ¹Molekulare Festkörperphysik, Philipps-Universität Marburg — ²Institut für Physik, Carl von Ossietzky Universität Oldenburg — ³Physics Dept., Humboldt-Universität zu Berlin & IRIS Adlershof

Charge-transfer excitons (CTX) occurring at molecular donor/acceptor interfaces are considered important intermediates for charge separation in photovoltaic devices. Co-crystalline pentacene:perfluoro-pentacene (PEN:PFP) films can be prepared with different molecular orientation on SiO2 and graphene substrates [1] and thus are well-suited model systems for detailed structure-property investigations of such CTX states. In this study, such crystalline PEN:PFP films with different molecular orientations are used to perform polarization and angular resolved UV/Vis absorption spectroscopy, in order to determine the direction of the transition dipole moment (TDM) of the CTX state, which is found to be perpendicular to the aromatic ring planes i.e. along the stacking direction. Interestingly, this orientation is different than for the singlet excitons of unitary acene films, which can be well-described by the Kasha-model using the TDMs of the single molecule HOMO-LUMO excitations that are oriented along the M-axis and thus constitutes an important benchmark system for a refined theoretical analysis of such molecular donor/acceptor systems. [1] D'Avino et al. Chem. Mater. 32, 3, 1261-1271 (2020)