Novel butterfly pyrene-based organic semiconductors for field effect transistors { Hengjun Zhang, a Ying Wang, a Kuizhan Shao, b Yunqi Liu,* a Shiyan Chen, a Wenfeng Qiu, a Xiaobo Sun, a Ting Qi, a Yongqiang Ma, a Gui Yu, a Zhongmin Su* b and Daoben Zhu* a Received (in Cambridge, UK) 1st November 2005, Accepted 1st December 2005 First published as an Advance Article on the web 5th January 2006 DOI: 10.1039/b515433b Novel butterfly pyrene derivatives functionalized with trifluoro- methylphenyl and thienyl aromatic groups in the 1-, 3-, 6- and 8-positions of pyrene cores 1 and 2 have been synthesized by Suzuki coupling reactions, and their crystal structures, optical and electrochemical properties investigated; additionally, the field effect transistor using 2 as the active material exhibited a p-type performance. Recently, organic semiconductors have gained a lot of interest through applications such as organic light emitting diodes (OLEDs), 1 solar cells 2 and organic field effect transistors (OFETs). 3 The interest in studying OFETs stems from the fact that these devices are easier to fabricate than traditional silicon based transistors, which require severe processing techniques, and also the likelihood of replacing amorphous silicon in applications such as identification tags, smart cards and display drivers that are intended for short term use and large scale manufacture. The design and synthesis of novel materials that possess a low threshold voltage, a high on/off ratio, and high mobility and stability under ambient and operating conditions are the major challenges in organic semiconductor research. Existing organic semiconductors can be roughly classified into linear, 4–10 star-shaped, 11 branched 12 or lamellar 13 molecules on the basis of their shape. Most organic semiconductors are linear molecules, such as pentacene, 4 oligothiophene, 5 polyfluorenes, 6 tetracene, 7 anthracene 8 and their derivatives. 9 Among them, pentacene is the most well-known linear organic semiconductor with the highest thin film mobility using a polymeric surface treatment, 10 but is only moderately stable in air or under illumination, and has a low solubility in organic solvents. Phthalocyanine and its derivatives are typical lamellar molecules, which have been investigated widely as p-type or n-type active materials in OFETs. 13 Nowadays, a few star-shaped and branched molecules are synthesized and used as semiconducting materials in OFETs because of their easy processibility and high solubility in organic solvents. 11–12 Here, we report the synthesis and characteri- zation of the first examples of novel butterfly pyrene derivatives with trifluoromethylphenyl and thienyl aromatic groups. Their performance as p-type semiconductors in FET devices is also presented. The synthesis of pyrene derivatives 1 and 2 were conveniently realized by Suzuki coupling reactions according to Scheme 1. The reaction of 4-trifluoromethylphenylboronic acid and 2-thiophene- boronic acid with 1,3,6,8-tetrabromopyrene in refluxing dioxane under a nitrogen atmosphere gave 1 and 2 in 75 and 77% yields, respectively. Both compounds 1 and 2 dissolve in common organic solvents, allowing these semiconductors to be easily purified by a combination of recrystallization and gradient sublimation. The compounds were characterized by 1 H NMR, MALDI-TOF, elemental analysis and X-ray crystallography. Differential scan- ning calorimetry (DSC) measurements showed sharp melting endotherm peaks at 231 uC for 1 and 308 uC for 2, respectively. Thermogravimetric analysis (TGA) measurements gave the thermal decomposition temperatures (T d ) 388 uC for 1 and 428 uC for 2, respectively. All the results shown in Table 1 indicate that the butterfly pyrene-based materials possess excellent thermal stability. This is a necessary feature of functional materials for applications in thin film molecular devices. Single crystals of each were obtained by slow evaporation of solvent from dichloromethane solutions. Fig. 1(a) and Fig. 1(b) show the ORTEP drawings of 1 and 2 and their atomic numbering schemes, respectively. Both molecules display an inner flat, symmetric molecular geometry, while the peripheral trifluoro- methylphenyl and thienyl units adopt twisted forms, connecting with the pyrene core like a flying butterfly. The torsion angles of 52.8 and 60.2u are observed between the pyrene and trifluoro- methylphenyl rings, and 55.1 and 57.8u between the pyrene and thienyl rings. The molecules pack in the herringbone motif, as shown in the ESI,{{ similar to pentacene. 14 The physical properties of newly prepared compounds 1 and 2 are listed in Table 1. The absorption maximum of 1, containing electron-withdrawing groups, is located at 381 nm, while a Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080, People’s Republic of China. E-mail: liuyq@mail.iccas.ac.cn b Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun, 130024, People’s Republic of China { Electronic Supplementary Information (ESI) available: Detailed experi- mental procedures with cyclic voltammograms and crystal packing views of 1 and 2. See DOI: 10.1039/b515433b Scheme 1 Synthetic routes to compounds 1 and 2. COMMUNICATION www.rsc.org/chemcomm | ChemComm This journal is ß The Royal Society of Chemistry 2006 Chem. Commun., 2006, 755–757 | 755