Oligotwistacene DOI: 10.1002/ange.201200949 Synthesis and Structure Characterization of a Stable Nonatwistacene** Jinchong Xiao, Hieu M. Duong, Yi Liu, Wenxiong Shi, Li Ji, Gang Li, Shuzhou Li, Xue-Wei Liu, Jan Ma, Fred Wudl,* and Qichun Zhang* As an important class of organic electronic materials, acenes have already received much attention in both fundamental investigations and practical applications. [1–5] Although theo- retical modelling and calculations suggest that larger acenes can have a singlet disjointed biradical character or an antiferromagnetic character in the ground state, [4] there are few successful studies on the synthesis and experimental characterization of larger acenes (> 7 repeating benzo units). Owing to difficult multistep synthetic approaches, tedious separation, poor solubility, and extreme instability (sensitivity to light, oxygen, and polymerization), [1–3, 6] linear polyacenes remain challenging systems. In order to avoid these draw- backs and approach the larger stable acenes, several groups have reported successful results by selectively adding protect- ing groups, such as phenyl, fluoride, arylthio, or silylethyne, on the periphery of the conjugated acene frameworks to increase solubility and enhance stability. [1–3, 5, 7] Our groups are particularly interested in acenes with rigid terminal pyrene units (Figure 1). The acene family containing rigid terminal pyrenes (or phenanthrenes) can be divided into two types: [6, 8, 9] double-terminal pyrenes (or phenanthrenes; type I, Figure 1) and single-terminal pyrene (or phenan- threne, type II, Figure 1). The non-bonding interactions between substituents (or even H atoms) on the twistacene backbone and the pyrene can cause the framework of the acenes to twist. [5, 7a, 8–10] We believe that this twist, together with selectively appended phenyl substitutents, offers enhanced protection of the larger acene molecules in this family from dimerization and oxidation. In fact, we have already reported several remarkably stable twisted acenes and heteroacenes containing single/double-terminating pyrene units. [5, 7a, 9, 11] Recently, we developed a clean reaction method to prepare the larger acenes and their derivatives in a pure state and in near quantitative yield from the corresponding precursors. [9, 11] The key step in this strategy is a retro-Diels– Alder process involving the thermal elimination of lactam bridges from soluble acene precursors (Scheme 1). This method, together with the twist concept, led us to believe that a higher twistacene could be prepared. Herein we report the synthesis and characterization of 6,8,10,17,19,21-hexa- phenyl-1.22,4.5,11.12,15.16-tetrabenzononatwistacene (1; Scheme 2). The desired precursor 2, was obtained in 22 % yield through a cycloaddition reaction between 3 and the aryne generated from 4 (Scheme 2; see the Experimental Section for full chemical names). [5a, 11] A reaction to eliminate the bridge, performed in either diphenyl ether (sealed tube at 330 8C; Scheme 2) or the solid state, proved to be an efficient way to form compound 1. Slowly cooling the diphenyl ether solution afforded cubic, dark-green crystals of 1. These crystals are stable in air for more than five days without any protection. Figure 1. Twistacene structures. Scheme 1. Clean reaction approach to higher acenes. [*] Dr. J. Xiao, [+] Dr. Y. Liu, Dr. W. Shi, Dr. G. Li, Prof.Dr. S. Li, Prof. Dr. Q. Zhang School of Materials Science and Engineering Nanyang Technological University Singapore 639798 (Singapore) E-mail: qczhang@ntu.edu.sg Homepage: http://www.ntu.edu.sg/home/qczhang/ Dr. H. M. Duong [+] Department of Chemistry, University of California Los Angeles, CA, 90095 (USA) L. Ji, Prof. X.-W. Liu School of Physical and Mathematical Sciences Nanyang Technological University 1 Nanyang Walk, Singapore, 637616 (Singapore) Prof. F. Wudl Department of Chemistry and biochemistry University of California Santa Barbara, CA, 93106 (USA) E-mail: Wudl@chem.ucsb.edu [ + ] These two authors made equal contribution to this paper. [**] Q.Z. acknowledges financial support from a start-up grant (Nanyang Technological University), an AcRF Tier 1 (RG 18/09) from MOE, the CREATE program (Nanomaterials for Energy and Water Management) from NRF, and the New Initiative Fund from NTU, Singapore. F.W. acknowledges support from the NSF while at UCLA. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201200949. A ngewandte Chemi e 1 Angew. Chem. 2012, 124,1–5  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü