CC BY 4.0 UnportedGraf, LukasKrupskaya, YuliaBüchner, BerndKnupfer, Martin2022-01-252022-01-252021https://oa.tib.eu/renate/handle/123456789/7928https://doi.org/10.34657/6969We have experimentally determined the momentum dependence of the electronic excitation spectra of para-quaterphenyl single crystals. The parallel arrangement of para-quaterphenyl molecules results in a strong Coulomb coupling of the molecular excitons. Such crystals have been considered to be a very good realization of the Frenkel exciton model, including the formation of H-type aggregates. Our data reveal an unexpected exciton dispersion of the upper Davydov component, which cannot be rationalized in terms of inter-molecular Coulomb coupling of the excitons. A significant reduction of the nearest neighbor coupling due to additional charge-transfer processes is able to provide an explanation of the data. Furthermore, the spectral onset of the excitation spectrum, which represents a heavy exciton resulting from exciton-phonon coupling, also shows a clear dispersion, which had been unknown so far. Finally, an optically forbidden excitation about 1 eV above the excitation onset is observed. © 2021 Author(s).enghttps://creativecommons.org/licenses/by/4.0/530Charge transferDispersionsExcited statesMolecular structureSingle crystalsCharge transfer processCoulomb couplingsElectronic excitation spectraExciton dispersionFrenkel exciton modelMolecular excitonsNearest-neighbor couplingParallel arrangementQuaterphenylArticle