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Issue 23, 2013
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Synthesis and structure of α-substituted pentathienoacenes

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Recent progress in thienoacene development has produced numerous high performance, air-stable organic semiconductor materials. Pentathienoacene (T5) thin film devices have shown poor performance despite promising computational studies, likely due to high mobility anisotropy and poor film morphology. 2,6-Bis-alkyl-pentathienoacene has been synthesized to enable solution-processing routes to better microstructures of T5-based devices. Soluble side groups are introduced to thieno[3,2-b]thiophene precursors through deprotonation at α-positions. Introduction of the sulfur bridge was achieved by Pd-catalyzed coupling reaction with bis(tri-n-butyltin)sulfide (Bu3SnSSnBu3), followed by final ring closure through oxidative coupling with CuCl2. This method achieves higher purity and higher yield than sulfide-quenched Li–Br exchange. UV-vis and fluorescence emission spectra show a bathochromic shift of ≈10 nm, indicating the introduction of alkyl chains decreases the HOMO–LUMO gap. X-ray analysis yields unit cells for 2,6-bis-octyl and 2,6-bis-dodecyl substituted T5s (C8-T5 and C12-T5, respectively). C8-T5 grows orthorhombic crystals with lattice parameters a = 1.15 nm, b = 0.43 nm and c = 3.05 nm; C12-T5 grows monoclinic crystals (c-unique) with unit cell with parameters a = 1.10 nm, b = 0.42 nm, c = 3.89 nm and γ = 92.9°. Both materials grow large (>50 μm), faceted, single crystals that are microscopically composed of alternating layers of semiconducting cores and insulating substitutions.

Graphical abstract: Synthesis and structure of α-substituted pentathienoacenes

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The article was received on 22 Jan 2013, accepted on 26 Apr 2013 and first published on 03 May 2013

Article type: Paper
DOI: 10.1039/C3TC30144C
J. Mater. Chem. C, 2013,1, 3686-3694

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    Synthesis and structure of α-substituted pentathienoacenes

    C. M. Shaw, X. Zhang, L. San Miguel, A. J. Matzger and D. C. Martin, J. Mater. Chem. C, 2013, 1, 3686
    DOI: 10.1039/C3TC30144C

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