Electronic, redox and charge transport properties of an unusual hybrid structure: a bis(septithiophene) bridged by a fused tetrathiafulvalene (TTF)†‡ Iain A. Wright, a Peter J. Skabara, * a John C. Forgie, a Alexander L. Kanibolotsky, a Blanca Gonz alez,x b Simon J. Coles, c Salvatore Gambino d and Ifor D. W. Samuel d Received 15th July 2010, Accepted 23rd September 2010 DOI: 10.1039/c0jm02293d A hybrid tetrathiafulvalene–oligothiophene compound has been synthesised, in which the fulvalene unit is fused on both sides to an end-capped septithiophene oligomer. The compound (1) has been studied by cyclic voltammetry, UV-vis spectroelectrochemistry and X-ray crystallography. The properties of this material are compared to the half-unit (9), which lacks the TTF core and contains only one septithiophene chain. In the case of the larger molecule, there are multiple and complex redox processes leading to the loss of 6–8 electrons per molecule. Charge generation layer time-of-flight measurements give maximum hole mobilities of ca. 1  10 5 cm 2 V 1 s 1 . Introduction By incorporating electron rich or deficient units into conjugated polymers and oligomers we have the potential to manipulate the HOMO and/or LUMO energy levels of the material, which is key to the development of semiconductor devices based upon poly- mer materials. 1–3 Tetrathiafulvalene (TTF) derivatives have been the focus of ongoing research towards the development of new functional materials, largely due to its reliable redox behaviour and the metallic conductivity or superconductivity observed in its charge-transfer salts. 4–9 Oligothiophenes are semiconducting species which have been intensively studied towards the genera- tion of many new organic electronic devices, including light emitting diodes, field effect transistors and solar cells. 2,10–14 TTF derivatives have been studied as components in field- effect transistors and there are several examples of materials with high mobilities, including thiophene–TTF hybrids. 15–19 In recent years we have been investigating oligothiophenes and poly- thiophenes that possess TTFs 20–25 and other redox active systems 26–30 fused directly to the backbone of the conjugated chain. Our interests arise from the complex redox behaviour resulting from the merging of two strong redox-active compo- nents. From these studies, we have found that, depending on the nature of the polymer, the fulvalene unit can either dominate the electroactivity of the polymer or participate in a hybrid redox state. 22 End-capped oligothiophenes are particularly attractive materials to study as they usually give well-defined redox signatures and stable charged intermediates, 23,31 allowing for more precise analysis of the complex electrochemical behaviour of these hybrid systems. In our previous work, the molecules developed bore TTF units stemming from the polythiophene chain and the signature of the TTF redox characteristics was clearly evident in electrochemical studies. In all these cases, the TTF system was fused directly to the conjugated chain through only one of the 1,3-dithiole rings, thereby retaining the signature oxidation of the second dithiole unit as an independent redox-active moiety. Here we report the synthesis and electrochemical study of a new hybrid molecule, featuring a TTF core fused at both ends of the molecule between two methyl end-capped septithiophene (7T) chains (1). The 7T chains also bear hexyl groups on the 3-position of the terminal thiophene rings to provide solubility. a WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, G1 1XL, UK. E-mail: peter.skabara@strath.ac.uk b Departamento de Qu ımica Inorg anica, Facultad de Ciencias, Universidad Aut  onoma de Madrid, Cantoblanco, 28049 Madrid, Espa~ na c School of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK d Organic Semiconductor Centre, SUPA, School of Physics & Astronomy, University of St Andrews, St Andrews, KY16 9SS, UK † Electronic supplementary information (ESI) available: Full experimental details for the synthesis of all new compounds and crystallographic data. CCDC reference numbers 783815, 783816. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c0jm02293d ‡ This paper is part of a Journal of Materials Chemistry themed issue in celebration of the 70th birthday of Professor Fred Wudl. x Present address: Departamento de Qu  ımica Inorg anica y Bioinorg anica, Facultad de Farmacia, Universidad Complutense de Madrid, Ciudad Universitaria, Madrid 28040, Espa~ na. 1462 | J. Mater. Chem., 2011, 21, 1462–1469 This journal is ª The Royal Society of Chemistry 2011 PAPER www.rsc.org/materials | Journal of Materials Chemistry Downloaded by St Andrews University Library on 14 June 2011 Published on 26 October 2010 on http://pubs.rsc.org | doi:10.1039/C0JM02293D View Online