Synthetic Metals 102 (1999) 14X-1489 Radical-ion salts based on C60-TTF fused dyads. J. Llacay, A. Perez-Benitez, M. Mas-Torrent, J. Vidal-Gancedo, J. Veciana and C. Rovira* lnstitut de Cihcia de Materials de Barcelona (CSIC). Campus UAB, 08193 Bellaterra, Spain Abstract Both radical-anion and radical- cation-salts derived from CN,-TIF dyads have been generated and studied in solution, displaying outstanding persistences. The dyad lc, having the best donor properties, is the only one that forms crystalline radical-cation salts by electrocrystallization which can be studied. The salt (lc), BF,, in spite of its mixed valence character, do not has good conducting behaviour. Keywords: Fullerenes and derivatives, organic conductors based on radical cation salts, electrocrystallization, electron spin resonance. 1. Introduction The use of Cc+)and its derivatives as constituents of organic materials is an area of keen interest since the beginning of the fullerene research [I]. There is substantial activity in the study of intramolecular charge transfer processes in CN, based dyads bearing different electron donor fragments [2], but much less is known about the use of such compounds to obtain intermolecular charge transfer complexes and salts [3]. We now present a study of the radical-ion salts derived from a new family of Cn,,-TTF dyads 1 a-c. 2. Results and discussion The synthesis of the CM:,-TTF dyads 1 has been carried out by a Diels-Alder reaction between Cho and the corresponding lTF diene precursors [4] in a 2:1 ratio. Reactions proceeded to give the monoadducts as major products [5,6]. NEt3 a R = COOCHl bR=H CRZCH, / oxidation \ reduction As cxpccted from the bichromophoric nature of dyads la-c, cyclic voltammograms show two reversible oxidation processes corresponding to the ‘ITF’s and up to four reversible reduction processes due to the Ch,, (Table 1). Reduction potentials are invariant when changing the addend, revealing the absence of strong electronic interactions between the two chromophores. By contrast, oxidation potentials are sensitive to the substituents of the TTF core. Thus, the gap between the first oxidation and the first reduction processes in these dyads (AE, in Table 1) can be tuned by changing the electronic characteristics of the substituents of the TI’F core. Table 1. CV data of compounds 1 a-c” Dyad E-l E-2 E-3 E-4 E+l E+2 Ah la’ -1.21 -1.63 -1.99 -2.57 0.13 0.65 1.34 lb -1.17 -1.53 -2.05 -2.49 -0.08 0.43 I .09 lc -1.18 -1.55 -2.06 -2.52 -0.15 0.41 I .03 a) Et,2 values in V(vs. Fc+/Fc, internal reference) of 1 in 0.1 M Bu4NPF6 solution (o-DCB) at room temperature using Pt as working and counter electrodes. b) AEO = EO,+l - Eg,-,. c) An additional quasi- reversible wave is observed at -2.24 V. The redox properties of dyads 1, permits generation of radical-cation and -anion cation derivatives by oxidation and reduction respectively (Figures I and 2). EPR g values and 33S hyperfine coupling constants (table 2), reveal that the spin density distribution of radical cations is mainly located on the TTF moiety whereas that of the radical anions is located on the fullerene cage. Table 2. EPR data corresponding to radical-ions from 1. Dyad radical-cation radical-anion I: aH (mT) as (mT) R la 2.0077 0. I96 (2H) 0.464 I 9997 0.382 1 I> 2.0077 0. I I9 (2H) 0.4 I2 I .9999 0. I49 (2H) 0.435 lc 2.0075 0. I32 (2H) 0 400 I 9996 0.080 (6H) 0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)007 15-2