Unilaterally Fluorinated Acenes: Synthesis and Solid‐State Properties

Abstract

The rapid development of organic electronics is closely related to the availability of molecular materials with specific electronic properties. Here, we introduce a novel synthetic route enabling a unilateral functionalization of acenes along their long side, which is demonstrated by the synthesis of 1,2,10,11,12,14‐hexafluoropentacene (1) and the related 1,2,9,10,11‐pentafluorotetracene (2). Quantum chemical DFT calculations in combination with optical and X‐ray absorption spectroscopy data indicate that the single‐molecule properties of 1 are a connecting link between the organic semiconductor model systems pentacene (PEN) and perfluoropentacene (PFP). In contrast, the crystal structure analysis reveals a different packing motif than for the parent molecules. This can be related to distinct F⋅⋅⋅H interactions identified in the corresponding Hirshfeld surface analysis and also affects solid‐state properties such as the exciton binding energy and the sublimation enthalpy.

Synthesis of 6,13-difluoropentacene

“…The λ max was determined to be at 597 nm, which corresponds to a HOMO-LUMO gap of ΔE = 2.08 eV. Comparison with the values of PEN (ΔE = 2.13 eV) [9] and PFP (ΔE = 1.99 eV) [9] shows that the electronic structure of F2PEN 5 lies in between these two.…”

“…While fluorine substituents in 2,3,9,10-positions (F4PEN 3) result in a larger HOMO-LUMO gap compared to PEN [7,8], substitution in the 6,13-positions leads to smaller band-gaps, similar to the unilaterally substituted F6PEN 4 [9].…”

“…They reported that the fluorination in the 2,3,9,10-positions resulted in a larger HOMO-LUMO gap compared to PEN, while PFP showed a smaller gap than PEN. Another example for a partially fluorinated pentacene is the F6PEN 4 [9]. Its unilateral substitution pattern leads to a disctinct electronic structure and a criss-cross packing motif, unlike the herringbone structure of 1-3.…”

Synthesis and Molecular Properties of Partially Fluorinated DNTTs**

“…This is in line with our observation that fluorinated aromatic molecules generally tend to crystallize in smaller crystallites than their non-fluorinated pendants. [30] To obtain deeper insights into the nature of unoccupied electronic states, we have utilized NEXAFS spectroscopy. The carbon K-edge NEXAFS spectrum of F 4 DNTT (8) (cf.…”

“…This is particularly pronounced for F 4 DNTT (8), which exhibits final states with mixed character, as it has also been observed also for unilaterally fluorinated acenes. [30] As DNTT topologically consists of naphthalene and thiophene units, a comparison of the corresponding signatures is useful. Indeed, the NEXAFS spectrum of DNTT can be well-described by the NEXAFS signatures of these units, [42,43] as indicated by the dashed lines (blue: naphthalene-like resonance, orange: thiophene-like resonance, more details are given in Supp.…”