Modulating the Electronic and Solid‐State Structure of Organic Semiconductors by Site‐Specific Substitution: The Case of Tetrafluoropentacenes

Abstract

The properties as well as solid‐state structures, singlet fission, and organic field‐effect transistor (OFET) performance of three tetrafluoropentacenes (1,4,8,11: 10, 1,4,9,10: 11, 2,3,9,10: 12) are compared herein. The novel compounds 10 and 11 were synthesized in high purity from the corresponding 6,13‐etheno‐bridged precursors by reaction with dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate at elevated temperatures. Although most of the molecular properties of the compounds are similar, their chemical reactivity and crystal structures differ considerably. Isomer 10 undergoes the orbital symmetry forbidden thermal [4+4] dimerization, whereas 11 and 12 are much less reactive. The isomers 11 and 12 crystallize in a herringbone motif, but 10 prefers π–π stacking. Although the energy of the first electric dipole‐allowed optical transition varies only within 370 cm−1 (0.05 eV) for the neutral compounds, this amounts to roughly 1600 cm−1 (0.20 eV) for radical cations and 1300 cm−1 (0.16 eV) for dications. Transient spectroscopy of films of 11 and 12 reveals singlet‐fission time constants (91±11, 73±3 fs, respectively) that are shorter than for pentacene (112±9 fs). OFET devices constructed from 11 and 12 show close to ideal thin‐film transistor (TFT) characteristics with electron mobilities of 2×10−3 and 6×10−2 cm2 V−1 s−1, respectively.

Unilaterally Fluorinated Acenes: Synthesis and Solid‐State Properties

“…In this case, the polar C À F bonds directly modify the energy levels of the psystem and, in the case of perfluorination, cause an inversion of the charge density distribution, as depicted in Figure 1 for pentacene. [14] So far, only a small number of partially fluorosubstituted pentacenes have been synthesized, mainly with symmetrical fluorination at the outer rings, [15] or in the case of asymmetric substitution only at the short molecular sides. [13,16] The latter molecules have a permanent dipole moment and geometrically combine two smaller aromatic subsystems (one being fluorinated) to one p-system with a push-pull character.…”

“…Scheme 1). [13,15,16] Due to regioselectivity problems within the [4+2] cycloadditions, unilaterally substituted pentacenes 6 require a different approach, with two bonds being formed in subsequent steps. Closure of the central ring via the bond marked in red could be possible from a key intermediate 7, which should be accessible in a convergent manner from two naphthalene building blocks 8 and 9 by formation of the bond marked in blue.…”

Impact of fluorination on interface energetics and growth of pentacene on Ag(111)

“…Overall, the influence of perfluorination on the multilayer growth and on the interfacial coupling of pentacene on clean metal surfaces is understood to a large extent. However, the impact of partial fluorination is less well studied, and thus we explored thin films of partially fluorinated PEN, namely 2,3,9,10-tetrafluoropentacene (F4PEN) [ 46 , 60 – 61 ]. F4PEN physisorbs on Au(111) [ 62 ] and chemisorbs on Cu(111), involving interfacial charge transfer and strong molecular distortions [ 63 ].…”

Unilateral fluorierte Acene: Synthese und Festkörpereigenschaften

“…In diesem Fall modifizieren die polaren CF-Bindungen direkt die Energieniveaus des p-Systems und verursachen im Fall der Perfluorierung eine Inversion der Ladungsdichteverteilung, wie in Abbildung 1 für Pentacen dargestellt. [14] Bisher wurde nur eine geringe Anzahl von teilweise fluorsubstituierten Pentacenen synthetisiert, hauptsächlich mit symmetrischer Fluorierung an den Außenringen [15] oder bei asymmetrischer Substitution nur an den kurzen molekularen Seiten. [13,16] Letztere Moleküle haben ein permanentes Dipolmoment und kombinieren geometrisch zwei kleinere aromatische Subsysteme (von denen eines fluoriert ist) zu einem p-System mit Push-pull-Charakter.…”

“…Hier stellen wir eine neuartige Synthesestrategie vor, mit der nahezu jede Art von Substitution realisiert werden kann. Unsere neue Route bietet Zugang zu einer Klasse unilateral substituierter Acene, die am Beispiel des unilateral fluorierten 1,2,10,11,12,14-Hexafluorpentacens (1) und des verwandten 1,2,9,10,11-Pentafluortetracens 2 [13,15,16] Aufgrund von Regioselektivitätsproblemen innerhalb der [4+2]-Cycloadditionen erfordern unilateral substituierte Pentacene des Typs 6 einen anderen Ansatz, wobei in getrennten Schritten zwei Bindungen nacheinander gebildet werden. Das Schließen des Zentralrings über die rot markierte Bindung kçnnte von einem Schlüsselintermediat 7 aus mçglich sein, das durch Aufbau der blau markierten Bindung von zwei Naphthalinbausteinen 8 und 9 konvergent zugänglich sein sollte.…”