5058 Chem. Commun., 2013, 49, 5058--5060 This journal is c The Royal Society of Chemistry 2013 Cite this: Chem. Commun., 2013, 49, 5058 Electron donors and acceptors based on 2,7-functionalized pyrene-4,5,9,10-tetraone† Shin-ichiro Kawano,z Martin Baumgarten,* Dennis Chercka, Volker Enkelmann and Klaus Mu ¨llen* An efficient synthesis of 2,7-dibromo- and diiodo-pyrene(4,5,8,19)- tetraones led to strong donors and acceptors based on pyrene. They are versatile building blocks for conjugated materials and can be further applied in molecular electronics. Polycyclic aromatic hydrocarbons (PAHs) have long played an important role in modern organic chemistry from a synthetic, theoretical and applied viewpoint. 1 More recently, PAH deriva- tives have been intensively studied as active components of electronic and optoelectronic devices. 2 In this regard, pyrenes are probably the best known organic chromophores, 3 while anthracenes 4 are used as emitters in organic light emitting diodes and pentacenes 5 are outstanding semiconductors in field effect transistors. Optimizing PAHs for electron and hole transport requires the synthesis of derivatives with either an electron rich or electron poor character. In the family of PAHs, pyrene itself is known as an electron donor, 6 and the conven- tional approach to functionalise this molecule is applied pre- dominantly at the 1,3,6,8-positions. 7 There exist very few reports where other positions have been tackled, like the inactive 2,7 positions (due to the nodal plane of the frontier orbitals) by introducing tert-butyl or pinacolborone both direc- ted by steric demands, or the 4,5,9,10-positions which most easily became accessible via the pyrene tetraone and its con- densation with diamines. 8,9 Here, we present a new synthetic strategy for creating a variety of both, electron deficient and electron rich pyrene derivatives 2–8. The synthesis of the target structures 2–8 is depicted in Scheme 1 and is based on pyrene-4,5,9,10-tetraone (1) which can be prepared in gram scales. 9 While pyrenes are usually halogenated in the 1,3,6,8-positions, our approach utilized the direct bromination or iodination in the 2,7-positions of 1, opening a new pathway for derivatives of pyrenes. The synthesis of 2,7-dibromopyrene-4,5,9,10-tetraone (2a) and 2,7-diiodo- pyrene-4,5,9,10-tetraone (2b) was easily performed by halo- genation with N-bromo- or N-iodosuccinimide in sulfuric acid, respectively. 10 Direct cyanation of 2a using CuCN to synthesize 2,7-dicyano-pyrene-4,5,9,10-tetraone (5) was not successful and resulted in an unidentified black solid. Therefore, the ketone- functions of compound 2a were protected with methyl groups via reductive alkylation with Na 2 S 2 O 4 and dimethyl sulfate. 11 The resulting product, 2,7-dibromo-4,5,9,10-tetra-methoxypyrene (3a), was obtained in a very good yield (82%). Subsequently, cyanation of compound 3a with CuCN led to 2,7-dicyano- 4,5,9,10-tetramethoxypyrene (4) (56%). 12 After deprotection with aluminium trichloride and subsequent oxidation with Scheme 1 (i) (2a) N-bromosuccinimide, H 2 SO 4 , at 45 1C, 2 h, 78%; (2b) N-iodosuccinimide, H 2 SO 4 , at 45 1C, 2 h, 74%; (ii) Na 2 S 2 O 4 , (n-Bu) 4 NBr, (CH 3 O) 2 SO 2 , KOH, THF, H 2 O, 40 1C, 1 h, 82%; (iii) CuCN, NMP, at 180 1C, 10 h, 56%; (iv) AlCl 3 , CH 2 Cl 2 , at 40 1C, 4 days; (v) Ag 2 O, THF, at 50 1C, 30 min, 20% for two steps; (vi) HN(CH 3 ) 2 in THF (6), HN(p-C 6 H 5 CH 3 ) 2 (7) Pd 2 DBA 3 , toluene, 95 1C, 18 h; (vii) NaOMe, CuI, toluene–DMF, 95 1C, 18 h, 62%. Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany. E-mail: baumgart@mpip-mainz.mpg.de, muellen@mpip-mainz.mpg.de; Fax: +49 6131 379100 † Electronic supplementary information (ESI) available: Experimental details, fluorescence spectra, cyclic voltammograms, X-ray structures and details, DFT calculations. CCDC 847344 (2a), 857532 (5), 857533 (6), 857534 (7), 857535 (8), 857537 (and mixed TCNQ cocrystals with 8) and 857536 (9). For ESI and crystallo- graphic data in CIF or other electronic format see DOI: 10.1039/c3cc39141h ‡ Present address: Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan. Received 21st December 2012, Accepted 10th April 2013 DOI: 10.1039/c3cc39141h www.rsc.org/chemcomm ChemComm COMMUNICATION Downloaded by Université Laval on 08/05/2013 18:03:56. Published on 10 April 2013 on http://pubs.rsc.org | doi:10.1039/C3CC39141H View Article Online View Journal | View Issue