The emerging field of organic electronics triggers the search for new molecular semiconductors and fluorophores. Since optoelectronic properties of molecular solids also depend crucially on molecular packing motifs, it is not sufficient to only consider single-molecule properties, but also to gain precise knowledge of the crystalline phases to understand structure−property relationships. Here, we analyze and compare structural and optoelectronic properties of perfluorinated acenes ranging from perfluoronaphthalene (PFN) via perfluoroanthracene (PFA) and perfluorotetracene (PFT) to perfluoropentacene (PFP), while previous studies, due to the lack of availability of PFA and PFT, were limited to PFN and PFP, which exhibit rather different crystal structures. Applying various crystallization techniques such as gradient sublimation, solution growth, and liquid-assisted organic molecular beam deposition, we identified different crystalline phases that allow closing this structural gap. A comparison of all known phases reveals clear trends in the molecular packing motifs, which are rationalized by corresponding Hirshfeld analyses. Using UV/vis and X-ray absorption spectroscopy, also optoelectronic solid state properties of the various compounds were analyzed, and from a comparison with the corresponding solution spectra, the exciton binding energies are estimated. In addition, we demonstrate that like PFP PFT also exhibits a π-stacked polymorph in films grown on graphene, where molecules are flat lying and adopt a slip-stacked packing. This interface-mediated phase is found to be stable only for PFP and PFT, while it is unstable for the smaller PFA. Finally, we demonstrate for the case of PFT that the different packing motifs occurring in the various phases have a strong influence on the photoluminescence spectra.

A series of molecules with oligophenylene backbone, thiolate anchoring group, and pentafluoro-λ6-sulfanyl (−SF5) tail group was synthesized and used as precursors to form self-assembled monolayers (SAMs) on Au(111) substrates. The resulting SAMs feature dense molecular packing, upright molecular orientation, and chemically homogeneous SAM-ambient interface, comprised entirely of the −SF5 moieties. These SAMs exhibit exceptional wetting and electrostatic properties, showing advancing water contact angles up to 103° and work function values up to 5.96 eV—probably the highest values reported for any aromatic monolayers on gold. They also feature a comparably low value of the tunnelling decay coefficient (0.38 ± 0.07 Å−1), typical of oligophenylene backbone, which is not affected by the introduction of the −SF5 group. The latter also hardly affects the current densities at a specific bias compared to analogous monolayers with other electronegative tail groups. The superior electrostatic and good charge transport properties of the designed, SF5-terminated SAMs make them potentially useful for interface engineering in organic electronics and photovoltaics.

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