A General Synthetic Approach to Novel Bis (tetracenyl) Aromatics for OFET Application
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A General Synthetic Approach to Novel Bis(tetracenyl) Aromatics for OFET Application Michael Roth and Matthias Rehahn Ernst-Berl-Institute of Chemical Engineering and Macromolecular Science, Darmstadt University of Technology, Petersenstrasse 22, 64287 Darmstadt, Germany, and Marcus Ahles, Roland Schmechel and Heinz von Seggern Department of Materials Science, Electronic Materials Division, Darmstadt University of Technology, Petersenstrasse 23, 64287 Darmstadt, Germany
Abstract A molecular tool box is presented, allowing the efficient synthesis of a broad variety of bis(tetracenyl) aromatics. These materials might be of considerable interest as semiconductors in organic field-effect transistors. The general synthetic strategy applied here involves Diels-Alder reactions of bromobenzocyclobutene derivatives and arene-1,4-endoxides[1], followed by transition-metal catalyzed condensation reactions of the formed 9-bromo-6,11-dihydrotetracene derivatives with aryldiboronic and -stannyl derivatives, respectively. In the final step, the resulting bis(dihydrotetracenyl) derivatives were dehydrogenated, giving the bis(tetracenyl) aromatics in good yields. They were characterized using NMR, UV-vis and mass spectrometry. Moreover, for some of these semiconductors the charge carrier mobility in thin film transistors has been determined. Introduction There is growing interest in organic field effect transistors (OFETs). They open up the opportunity of fabricating low-cost and/or flexible electronic circuits. It is assumed that these devices will play an important role in applications like RFID tags or display drivers on large plastic substrates[2]. The best organic semiconductor so far is pentacene. Its main disadvantage is the lack of stability against oxygen and water, and its tendency to disproportionate[3]. This might cause accelerated degradation of the organic semiconducting layers and complicate fabrication and processing. Tetracene, the shorter homologue of pentacene, is more stable but shows much lower charge-carrier mobility and non-ohmic contacts to most of the used source and drain electrodes[4]. Therefore it would be favorable to synthesize new tetracene derivatives with a higher molecular aspect ratio to improve the molecular ordering in the solid state, and to tune the electronic properties of the molecules, without loosing its superior chemical stability simultaneously. Following this strategy, there should be achievable higher field-effect mobility even in tetracenebased devices due to the higher degree of ordering, and may be lower contact barriers, improving the charge carrier injection. In order to achieve this goal, a retro-synthetic approach is needed which opens the possibility to synthesize regio-regularly substituted tetracenyl-based aromatics of increased aspect ratio. Only a few publications are known so far concerning the synthesis of substituted oligo-acenes[5]. Therefore we developed a new strategy which allows the convenient synthesis of a variety of potentially highly valuable new compou
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