The Influence of Terminal Push–Pull Substitution on the Electronic Structure and Optical Properties of Pentacenes

Non-symmetrical 6,13-disubstituted pentacenes bearing trifluoromethyl and aryl substituents have been synthesized starting from pentacenequinone. Diazapentacenes with a variety of fluorine substituents were prepared either via a Hartwig-Buchwald aryl amination route or by a SNAr strategy. As a result of a non-symmetric substitution pattern containing electron-donating substituents in combination with electron-accepting fluorine substituents, the synthesized compounds feature distinct molecular dipoles. All compounds are analyzed regarding their optoelectronic properties in solution with special focus on the frontier orbital energies as well as their molecular packing in the crystal structures. The analyses of isolated molecules are complemented by thin-film studies to examine their solid-state properties. A precise comparison between these and the molecular properties gave detailed insights into the exciton binding energies of these compounds, which are explained by means of a simple model considering the molecular packing and polarizabilities.

Section: Introductionmentioning

confidence: 99%

Efficient Syntheses of Novel Fluoro‐Substituted Pentacenes and Azapentacenes: Molecular and Solid‐State Properties

Schwaben

Münster

Klues

et al. 2015

“…For synthesis of the unsymmetrically substituted pentacene precursor, 1 was reacted with only 1 equiv of 2 under otherwise unchanged conditions giving monoadduct 6 in 38 % yield. Using our published procedures 6 was reacted with 1,2‐dibromo‐4,5‐difluorobenzene giving adduct 7 in 54 % yield. After DDQ oxidation, the ethenopentacene 8 was isolated in 85 % yield.…”

Section: Resultsmentioning

confidence: 99%

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

Geiger

Schundelmeier

Hummel

et al. 2020

Self Cite

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.

“…Pentacene derivatives with unsymmetrical substituents at terminal rings are quite rare in literature . The present synthetic strategy can easily be adopted to make this class of elusive compounds.…”

Section: Resultsmentioning

confidence: 99%

Template‐Assisted Benzannulation Route to Pentacene and Tetracene Derivatives and its Application to Construct Amphiphilic Acenes That Self‐Assemble into Helical Wires

Pal

Chang

Zeng

et al. 2017

Pentacene is one of the most versatile organic semiconductors. New synthetic strategies to construct the pentacene skeleton are imperative to produce pentacene derivatives with appropriate solubility, stability, and optoelectronic properties for various applications. This paper describes a template-directed approach to pentacene derivatives. In the retrosynthesis, the acene skeleton is viewed as a laddered double strand polyene instead of the more intuitive linearly fused hexagons. Based on this vision, the template strand of polyene is constructed with Wittig olefination, whereas the second strand is accomplished with Knoevenagel condensation to produce pentacene and tetracene derivatives. The synthetic scheme is flexible enough to generate an array of acene derivatives with substitution patterns that were hitherto difficult to access. Amphiphilic pentacene and tetracene derivatives were also synthesized by the template strategy. One pentacene based amphiphilic rod-coil molecule undergoes self-assembly to form helical wire structures that were visualized with TEM.