ELSEVIER Synthetic Metals 103 (1999) 22942295 Synthesis and design of potential polaronic ferromagnets J. N. Devine, J. A. Crayston and J.C. Walton School of Chemistry, Purdie Building, University of St. Andrews, St. Andrews, Fife,, KY16 9gJ U.K. Abstract Functionalised poly(thiophenes) with specific topologies have the potential to exhibit ferromagnctism. We have utilised this in the design and synthesis of various target monomers and have optimised synthetic routes towards them. These monomers have been chemically and electrochemically polymerised and the resultant materials characterised by variable temperature ESR and UV-VIS spectroscopy and cyclic voltammetry. Keywords: Coupling reactions, Heterocycle synthesis, Transition metal-catalysed reactions, Electrochemical doping and Electrochemical polymerisation. 1. Introduction Currently there is no such thing as a bulk ferromagnetic polymer, but its development would have certain distinct advantages: . . l . . 2. Molecular chemistry allows fine tuning of properties and structures of complex aggregates Lighter materials Greater processability Resistant to corrosion Attractive replacements for existing materials Organic Ferromagnets Consideration of the electronic structure of an oligophenylene carbene. [ I] . Chemical or electrochemical doping provides an efficient method of introducing a large number of s spins. . Full characterisation of polymer and molecular topology before the introduction of spins 4. Synthetic Target (1) R, =C,H,,,CH,; R,= H, C,,H, l m- Coupled benzene = FC , Tetrathiophene = S C U *Short SCU prevents bipolaron formation. l Alkyl groups provide solubility and processability. *Structural homogeneity maximises delocalisatiori. 3 . Polaronic Ferromagnets Fukotome [2] suggested that oxidised conjugated organic segments when linked by appropriate 7t topologies could produce novel magnetic materials. In the polaronic model a magnetic material consists of two types of building blocks [3]: the spin containing unit (SCU) and the ferromagnetic coupling unit (FC), which insures high spin pairwise interactions between SCU’s. The use of polaronic ferromagnets has several attractive features: Stability and robustness of conjugated organic molecules provides potential SCU’s 0379~6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PIl: SO379-6779(98)00635-3 5. Methods for Regioselective Coupling We initially chose the method shown in Scheme 1 to synthesise 3,4’-dialkyl-2,2’-bithiophenes 5. Scheme 1 R,-Br NiCl,(dppp)/O’C 2 , ! I 1. LDA fHF -78 to -40’C 40kn NBS / DMF 2. MgBr, -60 to -SC 2h && Jy -2&Fy:r lNiClz(dppp) -78% Pt