Hexaazatriisothianaphthenes: new electron-transport mesogens? Matthias Lehmann, a Vincent Lemaur, b Je ´ro ˆme Cornil, b,c Jean-Luc Bre ´das, b,c Simon Goddard, d Ilaria Grizzi d and Yves Geerts a, * a Laboratoire de Chimie des Polyme `res CP206/1, Universite ´ Libre de Bruxelles, Boulevard du Triomphe, 1050 Bruxelles, Belgium b Laboratory for Chemistry of Novel Materials, Center for Research in Molecular Electronics and Photonics, University of Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium c School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA d CDT Limited, Greenwich House, Madingley Rise, Madingley Road, Cambridge CB3 0HJ, England, UK Received 18 February 2003; revised 19 January 2004; accepted 27 January 2004 Abstract—Hexaazatriisothianaphthenes substituted with six alkylsulfanyl chains (propyl and dodecylsulfanyl) have been synthesised and their thermotropic, photophysical and oxidation – reduction properties characterised. Their synthesis has been motivated by the results of quantum-chemical calculations that point to efficient transport properties for these new electron-deficient mesogens since electron transport is predicted to be only slightly affected by rotational degrees of freedom in the discotic mesophase. q 2004 Elsevier Ltd. All rights reserved. 1. Introduction Discotic aromatic compounds emerge as attractive materials to promote efficient transport properties in organic-based devices such as light-emitting diodes, photovoltaic cells, or field effect transistors. Columnar liquid crystals combine the advantages of ease of preparation of oriented thin films, high order in the columns upon self-assembly, and self-healing capacity. Since such functional materials are used as one- dimensional semiconductors, both the orientation of the columnar structures at interfaces and the intracolumnar order of the aromatic cores play an important role in defining the device performance. 1 While a large number of p-type semiconducting columnar mesogens is known, few n-type materials have been reported to date. 2 Hexa- azatriphenylenes (HAT), incorporating six nitrogen hetero- atoms within a triphenylene core, are known to be electron- deficient and should thus facilitate electron injection. Columnar liquid crystals of derivatives based on a hexaazatriphenylene core have been obtained by supplying the electron-deficient core with three to six lateral chains. 3 In contrast, the electron-rich thiophene unit yields p-type semiconductivity in polythiophenes. Enhanced electron transport has been observed recently in conjugated polymers containing both thiophene and electron deficient units; 4 the substitution of sexithienyl with perfluorated carbon chains has also provided n-type semiconducting materials. 5 Our interest in electron-deficient columnar mesogens 3a has led us to combine the HAT and thiophene building blocks to generate compound 1 (Fig. 1) as potential electron transport material. We have introduced peripheral alkylsulfanyl chains to increase solubility, stabilise the radical anions, 6 and induce supramolecular columnar liquid crystalline order. The preparation of 1 has also been triggered by the results of quantum-chemical calculations indicating that the electron transport properties are expected to be improved in hexaazatriisothianaphthene compounds 0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2004.01.083 Tetrahedron 60 (2004) 3283–3291 1 2 Figure 1. Chemical structure of hexaazatriisothianaphthenes 1 not forming LC phases and of hexaazatrinaphthalenes 2 forming LC phases for R¼C n H 2nþ1 (n¼6, 8, 10, 12). 3a * Corresponding author. Tel.: þ32-2-650-5390; fax: þ32-2-650-5410; e-mail address: ygeerts@ulb.ac.be Keywords: Discotic mesogens; n-Type semiconductor; Electron mobility; Electronic splitting.