The First Example of a Polythiophene Bearing Fused Tetrathiafulvalene Units
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The first example of a polythiophene bearing fused tetrathiafulvalene units Peter J. Skabara,*a Donna M. Roberts,b Asim K. Ray,b Suresh S. Umare,†b Aseel K. Hassan,b Alexey V. Nabokb and Klaus Müllenc a
Department of Chemistry, University of Manchester, Manchester M13 9PL, UK
b
Materials Research Institute and the Physical Electronics and Fibre Optics Research
Laboratory, School of Engineering, Sheffield Hallam University, Sheffield S1 1WB, UK c
Max-Planck Institute for Polymer Research, Mainz 55128, Germany
†
On leave from the Department of Chemistry, Visvesvaraya Regional College of Engineering,
Nagpur-440011 (MS), India
ABSTRACT
The polymerization of a fused 2,5-dibromothieno-TTF derivative by Yamamoto procedures gave a highly electroactive polymer; doping the material with TCNQ increased the conductivity of the polymer by approximately two orders of magnitude.
INTRODUCTION
Conjugated polymers (CPs) and tetrathiafulvalene (TTF) derivatives represent two distinct families of electroactive species. In parallel, the syntheses, electronic properties and applications of both materials have been pursued enthusiastically for the last three decades. Whilst the major drive in these research areas has been fostered by unique, specific properties (e.g. electroluminescence in CPs1 and superconductivity in TTF charge-transfer salts),2 both types of material also feature common physical characteristics in their doped state (i.e. stable charged radical carriers, efficient electron/charge transport properties in the bulk material, low dimensional anisotropic conductivity), which may enable them to function jointly as hybrid electroactive species.3 Furthermore, the attainment of a CP exhibiting conductivity in the ground state, alongside the exceptional stacking ability of the TTF system, would be a much coveted achievement. C2.1.1
Inaugurated by the efforts of Bryce et al. towards the electropolymerization of compound 1,4 the 1990s has seen a growing interest in the marriage of TTF to conjugated polymers. The electrosynthesis of polythiophenes, linked to TTF units via saturated spacer groups, has been well established by the group of Roncali.5 However, the electropolymerization of TTF-thiophene monomers, in which the two redox-active moieties are directly bonded to each other (26 and 37) or fused (4),7,8 has so far been unsuccessful. Recently, TTF and extended-TTFs have been incorporated as main-chain components in CPs9 but, to the best of our knowledge, there is only one example in which TTF has been attached directly as a pendant side group to a CP, viz. the polyacetylene 5.10 Recently, we have prepared a terthiophene unit linked to TTF through a fused dithiin ring.11 The material has been successfully polymerized electrochemically, however, in the neutral state the two redox species are not connected through a conjugated link. In general, the extent of any electronic interaction between the TTF units and the polymer backbone will be maximised if the two dopable species are structurally integrated. The preparatio
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